A system, a device and a method for cooling a fuel in a fuel tank

Abstract

A device (10) for cooling a fuel in a fuel tank (12). The fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank, and vaporized prior to its consumption. The device comprises an ejector (20), a positive displacement flow path (30) configured to conduct fuel in a liquid state from the fuel tank to the ejector, a forced flow path (40) configured to conduct fuel in a gaseous state from the fuel tank to the ejector, a return flow path (50) configured to conduct a combined fuel to the fuel tank, and a consumption flow path (60) configured to conduct fuel from the fuel tank to a consumption device (15) for consumption of the fuel. The device further comprises a heat exchanger (70) configured to transfer heat from the return flow path to the consumption flow path.

Description

[0001]TITLE: A system, a device and a method for cooling a fuel in a fuel tank Field of the invention The present invention relates to a device for cooling a fuel in a fuel tank. The fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank. The fuel is configured to be vaporized prior to its consumption by a consumption device. The device comprises an ejector, a positive displacement flow path configured to conduct fuel in a liquid state from the fuel tank to the ejector, a forced flow path configured to conduct fuel in a gaseous state from the fuel tank to the ejector. The device further comprises a consumption flow path configured to conduct fuel from the fuel tank to the consumption device for consumption of the fuel. The present invention also relates to a system comprising the device, a method for cooling a fuel in a fuel tank, and use of such device and system. Background of the invention In various industrial and transportation applications, a type of fuel known as 'liquid gas fuel', hereafter referred as 'the fuel', is used and stored in a cooled and saturated condition within a fuel tank. The fuel is characterized in that it is configured to be stored mainly in the liquid state, while it needs to be vaporized prior to its use at a consumption device. The characteristic of the storage arrangement for the fuel is that the fuel exists simultaneously in both saturated liquid and saturated gaseous states. This cooled dual state is a result of that the fuel tank only is designed to maintain the fuel at a pressure below its saturation pressure at ambient temperature conditions. Storing the fuel at lower pressure offers cost advantages, particularly when dealing with large fuel volumes. However, this approach introduces challenges related to pressure and cooling of the fuel. As the fuel tank absorbs heat from its ambient environment, the liquid state fuel gradually undergoes vaporization, commonly known as 'boil-off gas'. This process results in a progressive increase in pressure within the fuel tank. Since the fuel tank is designed to withstand a pressure not exceeding a threshold pressure, measures must be implemented to continuously regulate and reduce the pressure inside the fuel tank such that the pressure is below the threshold pressure. One option is to release at least a portion of the fuel in the gaseous state from the fuel tank, effectively reducing the pressure within the fuel tank. However, this measure comes with significant drawbacks. The released fuel may be released without being utilized, leading to wastage and potential harm to the environment. Another approach involves extracting at least a portion of the fuel in the gaseous state from the fuel tank and using a compressor to convert the fuel back into its liquid state, and subsequently reintroducing the fuel in the liquefied state into the fuel tank. While this method conserves the fuel, the compressor approach has a set of disadvantages. Firstly, it requires energy for liquefying the fuel, which adds to the operational costs of the fuel tank. Additionally, the compressor involves moving parts that introduces a risk of gas leakage of the fuel. This approach is particularly challenging when dealing with hazardous substances such as ammonia, which demand adequate space for ventilation and certified personnel for handling such compressor. Furthermore, the movable parts of the compressor introduce reliability concern of the operation of such compressor systems. The combined factors of energy consumption, space requirements, adherence to governmental regulations concerning hazardous materials, and the reliability aspect contribute to an overall cost concern relating to the compressor-based solution to the problem. Summary of the invention An object of the invention is to provide an alternative solution or improvement relating to the above-mentioned problem. In particular, an object of the invention is to provide an improved device for cooling a fuel with low energy consumption. A further object of the invention is to provide an improved device for cooling a fuel, which device is compact and not requiring specific qualification for operating. Yet another object of the invention is to provide an improved device for cooling a fuel with high operative reliability. These objects are obtained by means of a device for cooling a fuel in a fuel tank, which fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank, wherein the fuel is configured to be vaporized prior to its consumption, The device comprises: - an ejector, - a positive displacement flow path configured to conduct fuel in a liquid state or mainly liquid state from the fuel tank to the ejector, - a forced flow path configured to conduct fuel in a gaseous state or mainly gaseous state from the fuel tank to the ejector, - a return flow path configured to receive fuel from the positive displacement flow path and the forced flow path, and conduct a combined fuel to the fuel tank, and - a consumption flow path configured to conduct fuel from the fuel tank to a consumption device for consumption of the fuel, wherein the device further comprises: - a heat exchanger configured to transfer heat from the return flow path to the consumption flow path. The fuel tank is configured to store the fuel in mainly the liquid state. However, due to the configuration of the fuel tank and its limited pressure holding capacity, the fuel is configured to be contained cooled in both the liquid state and the gaseous state within the fuel tank due to the interaction with the ambient environment. The fuel from the fuel tank is configured to be conducted from the fuel tank to the consumption device by means of the consumption flow path and consumed at the consumption device in the gaseous state. The fuel from the fuel tank accordingly needs to be transformed from a mainly liquid state to a mainly gaseous state prior to reaching the consumption device. The positive displacement flow path has the function of conducting a flow of the fuel in the liquid state or mainly the liquid state to the ejector. The positive displacement flow path comprises means for generating the flow of the fuel from the fuel tank to the ejector, such by means of a fuel pump. The forced flow path has the function of conducting a flow of the fuel in the gaseous state or mainly gaseous state to the ejector. The flow of the fuel is generated by means of the ejector in combination with positive displacement flow path, as will be discussed in further detail in the following. The ejector is configured to receive the fuel in a liquid state or mainly liquid state from the fuel tank by means of the positive displacement flow path. The receipt of the fuel from the positive displacement flow path by the ejector has the function of generating a pressure difference between the return flow path and the forced flow path that forces the fuel in the gaseous state or mainly gaseous state from the fuel tank through the forced flow path to the ejector, and which thereafter is combined with the fuel from the positive displacement flow path to form the combined fuel that is conducted through the return flow path. The return flow path has the function of conducting the combined fuel from the ejector back to the fuel tank. Accordingly, the combination of the positive displacement flow path, the forced flow path, the return flow path and the fuel tank form a closed circuit. It shall be understood that a respective outlet of the positive displacement flow path and the forced flow path at the fuel tank are located at different location at the fuel tank. The outlet of the positive displacement flow path is located at a position of the fuel tank where the fuel is predominately present in the liquid state. The outlet of the forced flow path is located at a position of the fuel tank where the fuel is predominately present in the gaseous state. It shall be understood that an inlet of the return flow path to the fuel tank preferably is located at a different position than the outlets of the positive displacement flow path and the forced flow path. The heat exchanger is arranged between the return flow path and the consumption flow path. The heat exchanger has the function of conducting heat from the combined fuel in the return flow path to the fuel in the consumption flow path. Thereby, the combined fuel in the return flow path is cooled prior to being returned to the fuel tank. Simultaneously, the fuel in the consumption fuel path is heated such that the fuel is at least partly vaporized or brought to a state closer to being vaporized. The device has the advantage of taking heat from the combined fuel in the return flow path, thereby cooling the fuel in the fuel tank and reducing the pressure in the fuel tank, and simultaneously heating the fuel in the consumption fuel path. The invention further has the advantage of using an ejector in the cooling of the fuel in the fuel tank. The ejector is a component that is configured to generate the pressure difference between the return flow path and the fuel tank without use of movable parts, such as a compressor. Thereby, the reliability of the device is improved compared with devices comprising compressors. By means of using the ejector, the invention further has the advantage that the risk of leakage of the gaseous fuel or mainly gaseous fuel that is extracted from the fuel tank by means of the forced flow path is reduced. As a result of this, the device does not require dedicated space for ventilation of leakage of gaseous fuel, as is the case for the devices comprising compressors. Furthermore, in the case when the fuel mainly comprises hazardous substances, such as ammonia, the device of the invention has the advantage of not requiring certified personnel for operating the device. According to an embodiment of the invention, the return flow path comprises a return flow pressure regulating arrangement configured to regulate a pressure of the combined fuel at the heat exchanger such that the pressure is set to exceed a value or enters an interval in which a ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval. The pressure is regulated by the return flow pressure regulating arrangement to a pressure that a value or enters an interval where the ratio between the liquid state fuel and the gaseous state fuel is desired, in particular such that the ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval. From the perspective of cooling the combined fuel in the return flow path, a high pressure is desired, which results in a high ratio between the liquid state fuel and the gaseous state fuel. However, a drawback of a high pressure in the return flow path is that the positive displacement flow path is required to conduct the fuel in the liquid state or mainly liquid state at a high flow, which requires energy from the device. Accordingly, for the purpose of finding a balance between the cooling of the fuel in the return flow path and the energy consumption of the device, a balance is desired that is reflected in that the return flow pressure regulating arrangement is controlled to set the pressure such that the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval. According to an embodiment of the invention, the return flow pressure regulating arrangement comprises: - a return flow sensor arrangement configured to sense the ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on said ratio of the combined fuel in the return flow path, - a return flow pressure control valve located at the return flow path between the fuel tank and the heat exchanger, wherein the device further comprises; - a control unit configured to receive information from the return flow sensor arrangement on the ratio between the liquid state fuel and the gaseous state fuel or the entity dependent on said ratio of the combined fuel in the return flow path, and on basis of the information control the pressure return flow pressure control valve such that the pressure is set to exceed the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval. The control of the pressure such that the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval is done by means of information on the ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on said ratio of the combined fuel in the return flow path from return flow sensor arrangement. In view of the information, the return flow pressure control valve is controlled by means of the control unit such that the pressure is set to exceed the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval. According to an embodiment of the invention, the return flow path comprises a return flow pressure regulating arrangement configured to regulate a pressure of the combined fuel at the heat exchanger such that the pressure is set to exceed a predetermined pressure value or enter a predetermined pressure interval. The pressure is regulated by the return flow pressure regulating arrangement to a pressure of the combined fuel at the heat exchanger such that the pressure is set to exceed a predetermined pressure value or enter a predetermined pressure interval. The pressure exceeding the predetermined pressure value or in the predetermined pressure interval is known to provide a desirable ratio between the liquid state fuel and the gaseous state fuel. According to an embodiment of the invention, the return flow pressure regulating arrangement comprises - a return flow sensor arrangement configured to sense the pressure or an entity dependent on the pressure of the combined fuel in the return flow path, - a return flow pressure control valve located at the return flow path between the fuel tank and the heat exchanger, wherein the device further comprises; - a control unit configured to receive information from the return flow sensor arrangement on the pressure or an entity dependent on the pressure of the combined fuel in the return flow path, and on basis of the information control the return flow pressure control valve such that the pressure of the combined fuel at the heat exchanger is set to exceed the predetermined pressure value or enters the predetermined pressure interval. The return flow sensor arrangement is sensing the pressure or the entity dependent on the pressure of the combined fuel in the return flow path. The control unit is configured to receive information on the pressure or the entity dependent on the pressure. The control unit is configured, on basis of the information, to control the return flow pressure control valve such that the pressure the pressure of the combined fuel at the heat exchanger is set to exceed the predetermined pressure value or enters the predetermined pressure interval. According to an embodiment of the invention, the return flow sensor arrangement comprises at least one of a pressure sensor, a liquid level sensor, and temperature sensor. According to an embodiment of the invention, the positive displacement flow path comprises at least one fuel pump configured to generate a flow of the fuel in a liquid state from the fuel tank to the ejector. The function of the fuel pump is to generate the flow of the liquid state fuel or mainly liquid state fuel from the fuel tank to the ejector. The fuel pump is preferably a fuel pump selected from the group of positive displacement pumps and centrifugal pumps. According to an embodiment of the invention, the consumption flow path is configured to receive fuel from the positive displacement flow path. By providing the consumption flow path from the positive displacement flow path a combined fuel pump may be used for conducing fuel in the positive displacement flow path and the consumption flow path. Thereby, the design of the device is simplified and less components are required. According to an embodiment of the invention, the consumption flow path is configured to be operated at a first pressure and the positive displacement flow path is configured to be operated at a second pressure, wherein the second pressure is higher than the first pressure. By means of operating the device such that the second pressure is higher than the first pressure, the efficiency of operating the device is improved. According to an embodiment of the invention, the device comprises a first type fuel pump and a second type fuel pump, wherein the first type fuel pump is configured to pressurize the consumption flow path to the first pressure, and wherein the first type fuel pump and the second type fuel pump together are configured to pressurize the positive displacement flow path to the second pressure. By means of using the first type fuel pump for pressurizing the consumption flow path to the first pressure and the combined effect of the first type fuel pump and the second type fuel pump for pressurizing the positive displacement flow path to the second pressure, the efficiency of operating the device is improved. The first type fuel pump is a low-pressure fuel pump that is configured to operate at the pressure level of the first pressure. The second type fuel pump is a high-pressure fuel pump that is configured to operate at the pressure level of the second pressure. The first fuel pump is assisting the second fuel pump in reaching the second pressure. According to an embodiment of the invention, the device is configured hold and conduct the fuel in the form of Ammonia, wherein the first pressure is configured to be in the interval of 1 to 10 bar, preferably 2 to 8 bar, and wherein the second pressure is configured to be in the interval of 70 to 90 bar, preferably 75 to 85 bar. According to an embodiment of the invention, the device is configured hold and conduct the fuel in the form of Liquid Natural Gas (LNG), wherein the first pressure is configured to be in the interval of 1 to 10 bar, preferably 2 to 8 bar, and wherein the second pressure is configured to be in the interval of 250 to 400 bar, preferably 300 to 350 bar. According to an embodiment of the invention, the consumption flow path comprises a consumption flow regulating arrangement comprising a consumption flow control valve configured to regulate the flow of the fuel from the fuel tank to the heat exchanger, and a consumption flow sensor, wherein the device further comprises a consumption flow control unit configured to control the consumption flow control valve based on information from the consumption flow sensor. By means of the consumption flow path the pressure of the fuel at the heat exchanged can be controlled. According to an embodiment of the invention, the device comprises a liquid fuel outlet configured to introduce fuel in the liquid state from the fuel tank to the positive displacement flow path. The function of the liquid fuel outlet is to provide fuel in the liquid state to the positive displacement flow path. The liquid fuel outlet is configured to be located at position of the tank where the fuel predominately is in the liquid state, such as a low part of the fuel tank. According to an embodiment of the invention, the device comprises a gaseous fuel outlet configured to introduce fuel in the gaseous state from the fuel tank to the forced flow path. The function of the gaseous fuel outlet is to provide fuel in the gaseous state to the forced flow path. The gaseous fuel outlet is configured to be located at a position of the fuel tank where the fuel predominately is in the gaseous state, such as an upper part of the fuel tank. According to an embodiment of the invention, the device comprises a combined fuel inlet configured to introduce the combined fuel from the return flow path into the fuel tank. The function of the combined fuel inlet is to introduce the fuel from the return flow path that was cooled by the heat exchanger back to the fuel tank. The return flow path may be located at different positions at the fuel tank at a distance from the liquid fuel outlet and the gaseous fuel outlet. Preferably, the combined fuel inlet is arranged at an upper part of the fuel tank. According to an embodiment of the invention, the device is configured hold and conduct the fuel selected from the group of Ammonia, Liquid Natural Gas (LNG), Liquefied Petroleum Gas (LPG), Ethylene, Propylene, Dimethyl Ether (DME), Butane, Isobutane. The above objects of the invention are further obtained by means of a system comprising a fuel tank, a device according to any of above embodiments, and a consumption device for consumption of the fuel. According to an embodiment of the invention, the consumption device is an engine. According to an embodiment of the invention, the consumption device is a fuel cell. The above objects of the invention are further obtained by means of method for cooling a fuel in a fuel tank, which fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank, wherein the fuel is configured to be vaporized prior to its consumption. The method comprises the steps of: - conducting the fuel in a liquid state from the fuel tank by means of a positive displacement flow path to an ejector, thereby generating a flow of the fuel in a gaseous state from the fuel tank by means of a forced flow path to the ejector, which results in a flow of a combined fuel by means of the return flow path from the ejector to the tank, - conducting the fuel by means of a consumption flow path from the fuel tank to a consumption device for consumption of the fuel, and - conducting heat from the combined fuel in the return flow path to the fuel in the consumption flow path. According to an embodiment of the invention, the method further comprises: - regulating the pressure of the combined fuel in the return flow path at the heat exchanger to exceed a value or enters a pressure interval in which a ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval. According to an embodiment of the invention, the method further comprises: - receiving information on the ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on said ratio of the combined fuel in the return flow path, and - controlling the pressure in the return flow path at the heat exchanger on basis of said information such that the pressure is set to the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval. According to an embodiment of the invention, the method further comprises: - regulating the pressure of the combined fuel in the return flow path at the heat exchanger such that the pressure exceeds a predetermined value or enters a predetermined pressure interval. According to an embodiment of the invention, the method further comprises: - receiving information on a pressure of the combined fuel in the return flow path at the heat exchanger, and - controlling the pressure in the return flow path at the heat exchanger on basis of the information such that pressure is set to exceed a predetermined value or enters a predetermined interval. According to an embodiment of the invention, the method further comprises: - receiving information on a pressure of the fuel in the consumption flow path at the heat exchanger, and - regulating a pressure of the fuel in the consumption flow path such that the pressure at the heat exchanger is set to exceed a predetermined pressure value or enters a predetermined pressure interval. According to an embodiment of the invention, the method further comprises: - pressurizing the consumption flow path to a first pressure, and - pressurizing the positive displacement flow path to a second pressure, wherein the second pressure is higher than the first pressure. According to an embodiment of the invention, the fuel in the form of Ammonia, and the first pressure is in the interval of 1 to 10 bar, preferably 2 to 8 bar, and the second pressure is in the interval of 70 to 90 bar, preferably 75 to 85 bar. According to an embodiment of the invention, the fuel in the form of Liquid Natural Gas (LNG), and the first pressure is in the interval of 1 to 10 bar, preferably 2 to 8 bar, and the second pressure is in the interval of 250 to 400 bar, preferably 300 to 350 bar. The above objects of the invention are further obtained by means of use of a device according to any of above embodiments. The above objects of the invention are further obtained by means of use of a system according to any of above embodiments. Description of the figures Embodiments of the present invention will now be described, by way of example only, with reference to the following figures, wherein: Figure 1a shows an embodiment of a system and a device for cooling a fuel in a fuel tank, Figure 1b shows a further embodiment of a system and a device for cooling a fuel in a fuel tank, and Figure 2 shows a flow chart of method for cooling a fuel in a fuel tank according to an embodiment of the invention. Description of preferred embodiments of the invention In fig.1 is an embodiment of a system 1 and a device 10 for cooling a fuel in a fuel tank 12 disclosed. The fuel is configured to be vaporized prior to its consumption at a consumption device 15, such as an engine or a fuel cell. The system 1 comprises the device 10, the fuel tank 12 and the consumption device 15. According to an embodiment of the invention, the fuel is ammonia and the consumption device 15 is one of a fuel cell or an ammonia engine. For example, the system 1 and device 10 are preferably applied on ships and other marine installations where fuel is needed for power supply continuously. The fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank 12 due to that the fuel tank 12 is designed to maintain the fuel at a pressure below the fuel’s saturation pressure at ambient temperature conditions. Consequently, a portion of the fuel within the fuel tank 12 gradually transforms from the liquid state to the gaseous state, known as 'boil-off gas'. This transition of the fuel results in a gradual increase in pressure within the fuel tank 12 as is discussed in the section ‘background of the invention’. The liquid state fuel is mainly located at a lower part of the fuel tank 12 and the gaseous state fuel is mainly located at an upper part of the fuel tank 12. The device 10 comprises an ejector 20, a positive displacement flow path 30, a forced flow path 40 and a return flow path 50 that together with the fuel tank 12 form a closed circuit for the fuel as will be discussed in the following. The positive displacement flow path 30, the forced flow path 40 and the return flow path 50 are all fuel paths that comprises conductors, such as fuel pipes, configured to conduct the fuel. The positive displacement flow path 30, the forced flow path 40 and the return flow path 50 are all connected to different part of the ejector 20. The ejector 20 is configured to receive fuel in a liquid state or mainly liquid state from the fuel tank 12 by means of the positive displacement flow path 30. The positive displacement flow path 30 is configured to generate a flow of the fuel in a liquid state or mainly liquid state from the fuel tank 12 to the ejector 20. The positive displacement flow path 30 comprises a liquid fuel outlet 32 from the fuel tank 12 for introducing fuel in the liquid state or mainly liquid state to the positive displacement flow path 30, and a fuel pump 34 for generating a flow of the fuel in the liquid state or mainly liquid state to the ejector 20. In the disclosed embodiment of the invention, the liquid fuel outlet 32 is indicated at a bottom portion of the fuel tank 12. However, it shall be understood that the liquid fuel outlet 32 may be arranged at a different location on the fuel tank 12 as long as predominately fuel in the liquid state or mainly liquid state is introduced into the positive displacement flow path 30. In the disclosed embodiment of the invention, the fuel pump 34 is indicated at a bottom portion of the fuel tank 12. However, it shall be understood that the fuel pump 34 may be arranged at different location as long as the fuel pump 34 is enabled to generate a flow of the fuel in the liquid state or mainly liquid state through the positive displacement flow path 30 and to the ejector 20. The ejector 20 is configured, based on the receipt of the fuel in the liquid state or mainly liquid state through the positive displacement flow path 30, to generate a pressure difference between the return flow path 50 and the forced flow path 40 that forces the fuel in the gaseous state or mainly gaseous state from the fuel tank 12 through the forced flow path 40 to the ejector 20. The ejector 20 is configured to generate the pressure difference between the return flow path 50 and the forced flow path 40 on basis of Bernoulli's principle. The function of the ejector 20 is to generate a flow of a combined fuel through the return flow path 50 back to the fuel tank 12. The combined fuel is a mixture of the fuel from the positive displacement flow path 30 and the forced flow path 40. Accordingly, the combined fuel is mixture of liquid state fuel and gaseous state fuel. The forced flow path 40 comprises a gaseous fuel outlet 42 from the fuel tank 12 for introducing fuel in the gaseous state or mainly gaseous state to the forced flow path 40. The return flow path (50) comprises a combined fuel inlet 52 configured to introduce the combined fuel that is conducted from the ejector 20 through the return flow path (50) into the fuel tank 12. The generated pressure difference between the return flow path 50 and the forced flow path 40 is configured to force the fuel in the gaseous state or mainly gaseous state from gaseous fuel outlet 42 to the ejector 20, and thereafter to be combined with the fuel from the positive displacement flow path 30 into the combined fuel in the return flow path 50 that is conducted from the ejector 20 to the fuel tank 12. In the disclosed embodiment of the invention, the gaseous fuel outlet 42 is indicated to be located at a top portion of the fuel tank 12. However, it shall be understood that the gaseous fuel outlet 42 may be arranged at a different location on the fuel tank 12 as long as predominately fuel in the gaseous state or mainly gaseous state is introduced into the forced flow path 40 through the gaseous fuel outlet 42. In the disclosed embodiment of the invention, the combined fuel inlet 52 is indicated to be located at a top portion of the fuel tank 12. However, it shall be understood that the combined fuel inlet 52 may be arranged at a different location on the fuel tank 12. However, the combined fuel is preferably introduced at a location of the fuel tank 12 where the fuel is predominately in the gaseous state. The device 10 further comprises a consumption flow path 60 configured to conduct fuel from the fuel tank 12 to the consumption device 15 for consumption of the fuel. The consumption flow path 60 comprises a conductor, such as a fuel pipe, configured to conduct the fuel to the consumption device 15. The fuel is configured to be vaporized prior to being consumed at the consumption device for 15. The consumption flow path 60 comprises a consumption fuel outlet 62 configured to introduce fuel into the consumption flow path 60. In the disclosed embodiment, the consumption fuel outlet 62 is connected to the positive displacement flow path 30 and receives fuel in the liquid state or mainly liquid state from the positive displacement flow path 30. The fuel pump 34 is configured to generate a flow of the fuel that is conducted both through the positive displacement flow path 30 and the consumption flow path 60. It shall be understood that the consumption fuel outlet 62 may be arranged at a different location, such on bottom portion of the fuel tank 12. It shall further be understood that the consumption flow path 60 may comprise a separate fuel pump for generating a flow of the fuel through the consumption flow path 60 to the consumption device 15. According to an embodiment, the device is configured to be operated such that the consumption flow path 60 is set to a first pressure and the positive displacement flow path 30 is set to a second pressure, wherein the second pressure is higher than the first pressure. The device 10 further comprises a heat exchanger 70 configured to transfer heat from the return flow path 50 to the consumption flow path 60. The heat exchanger 70 comprises a heat receipt portion 72 configured to be arranged at or in vicinity of the return flow path 50 and a heat discharge portion 74 configured to be arranged at or in vicinity of the consumption flow path 60. The heat exchanger 70 is configured such that the heat receipt portion 72 absorbs heat from the return flow path 50. Thereby, the combined fuel in the return flow path 50 is cooled. Accordingly, the combined fuel in the return flow path 50 is cooled prior to being returned to the fuel tank 12. Thereby, the pressure in the fuel tank 12 is reduced. Preferably, the device 10 is configured to be operated such that the heat exchanger 70 increases a ratio between the liquid state fuel and the gaseous state fuel of the combined fuel before it is being introduced into the fuel tank 12. The heat exchanger 70 is configured such that the absorbed heat is transferred to the heat discharge portion 74 that is configured to discharge the heat to the fuel of the consumption fuel path 60. Thereby, the conducted fuel in the consumption fuel path 60 is heated such that the fuel is at least partly vaporized or brought to a state closer to being vaporized. The device 10 has the advantage of utilizing the heat in the fuel in the gaseous state for heating the fuel that conducted to the consumption device 15. Thereby, cooling of the fuel and reduction of the pressure in the fuel tank 12 are obtain while heating the fuel for the consumption device 15. This has further the advantage of improved reliability of the device 10 compared with the use of a compressor. Furthermore, the risk of leakage of the fuel is reduced compared with prior art device, which has the advantage or requiring less space for ventilation and not requiring use of qualified operator for operating the device 10 of the invention. In the disclosed embodiment, the return flow path 50 comprises a return flow pressure regulating arrangement 80 configured to regulate a pressure of the combined fuel at the heat exchanger 70. The return flow pressure regulating arrangement 80 comprises a return flow pressure control valve 82 arranged at the return flow path 50 between the heat exchanger 70 and the combined fuel inlet 52. By means of the return flow pressure regulating arrangement 80, the pressure of the combined fuel of the return flow path 50 is configured to be controlled. According to an embodiment of the invention, the return flow pressure regulating arrangement 80 is configured to regulate a pressure of the combined fuel at the heat exchanger 70 such that the pressure is set to exceed a value or entering an interval in which a ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval. In an embodiment of the invention, the return flow pressure regulating arrangement 80 comprises a return flow sensor arrangement 84 and a return flow control unit 86 configured to receive information from the return flow sensor arrangement 84. According to an embodiment of the invention, the return flow sensor arrangement 84 comprises a sensor configured to configured to sense a ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on the ratio of the combined fuel in the return flow path 50. The return flow control unit 86 is configured to receive information from the return flow sensor arrangement 84 on the ratio between the liquid state fuel and the gaseous state fuel or the entity dependent on the ratio of the combined fuel in the return flow path 50. Based on the information, the return flow control unit 86 is configured to control the return flow pressure control valve 82 such that the pressure is set to exceed the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval. According to an embodiment of the invention, the return flow sensor arrangement 84 comprises a sensor configured to sense the pressure or an entity dependent on the pressure of the combined fuel in the return flow path 50. The return flow control unit 86 is configured to receive information from the return flow sensor arrangement 84 on the pressure or an entity dependent on the pressure of the combined fuel in the return flow path 50. Based on the information, the return flow control unit 86 is configured to control the return flow pressure control valve 82 such that the pressure of the combined fuel at the heat exchanger 70 is set to exceed a predetermined pressure value or enters a predetermined pressure interval. In the disclosed embodiment, the consumption flow path 60 comprises a consumption flow pressure regulating arrangement 90 configured to regulate a pressure of the fuel in the consumption flow path 60 at the heat exchanger 70. The consumption flow pressure regulating arrangement 90 comprises consumption flow pressure control valve 92 arranged at the consumption flow path 60 between the heat exchanger 70 and the consumption fuel outlet 62, By means of the consumption flow pressure regulating arrangement 90, the pressure of the fuel of the consumption flow path 60 is configured to be controlled. The consumption flow pressure regulating arrangement 90 is configured to be controlled for the purpose of delivery fuel gas to the consumption device 15. The consumption flow pressure regulating arrangement 90 preferably comprises consumption flow sensor arrangement 94 and consumption flow control unit 96 configured to receive information from the consumption flow sensor arrangement 94, such on the pressure of the fuel at the heat exchanger 70. The consumption flow pressure regulating arrangement 90 may be operated correspondingly to the return flow pressure regulating arrangement 80, however with the purpose of enabling the fuel in the consumption flow path 60 to be delivered to the consumption device 15. It shall be understood that separate or alternative a common control unit may be used for the return flow control unit 86 and the consumption flow control unit 96. According to an embodiment of the invention, the device 10 comprises a further heat exchanger 100 at the consumption flow path 60. The further heat exchanger is configured to receive heat from an external heat source and transfer the heat to the fuel of the consumption flow path 60. In the case where the device 10 is applied to a ship, the further heat exchanger 100 may receive heat from the sea water. By means of the further heat exchanger 100, it is assured that the fuel is sufficiently vaporized and heated prior to being conducted to the consumption device 15. It shall be understood that the further heat exchanger 100 has the function to assure the fuel in the consumption flow path 60 becomes sufficiently vaporized and heated. The need for heating in the heat exchanger 100 is for example dependent of the configuration of the device 10 and the applicable consumption device 15. According to an embodiment of the invention, the device 10 comprises a by-pass flow pass 110 between the return flow path 50 and the consumption flow path 60. The by-pass flow path 110 comprises a by-pass control valve 112 configured to be controlled in order to bleed some of the gaseous state fuel from the combined fuel in the return flow path 50. Thereby, the ratio between the liquid state fuel and the gaseous state fuel of the combined fuel in the return flow path 50 may be controlled so the ratio is increased. The by-pass flow path 110 comprises a conductor, such as fuel a pipe, configured to conduct a portion of the fuel in the gaseous state fuel from the combined fuel in the return flow path 50 to the consumption flow path 60. The by-pass flow path 110 may for example be used in a situation where there is an indication of nitrogen gas in the combined fuel of the return flow path 50. The nitrogen gas is used when cleaning the conductors of the device and the complete removal of the nitrogen gas may be difficult. The presence of the nitrogen gas in the combined fuel of the return flow path 50 may reduce the heat exchanger’s 70 efficiency of transferring heat from the return flow path 50 to the consumption flow path 60. Alternatively, the by-pass flow path 110 may be used in a situation where the ratio between the liquid state fuel and the gaseous state fuel of the combined fuel in the return flow path 50 is lower than desired. For example, in the case where the heat exchanger is incapable of transferring sufficient heat from the combined fuel in the return flow path 50 to the consumption flow path 60. By draining some of the gaseous state fuel from the combined fuel, the ratio between the liquid state fuel and the gaseous state fuel may be improved for the operation of the device 10. According to an embodiment of the invention, the device 10 comprises a disposal flow path 120 for temporary operational mode, where a portion of the gaseous state fuel from the combined fuel in the return flow path 50 is disposed. The disposal flow path 120 comprises a disposal control valve 122 and a disposal device 125. The disposal device 125 is configured to dispose fuel conducted to it during the temporary operational mode. Accordingly, the disposed fuel conducted through the disposal flow path 120 is permanently removed from the fuel tank 12. The disposal flow path 120 is configured to be used in corresponding manner and situation as for the by-pass flow path 110. The disposal flow path 120 comprises a conductor, such as a fuel pipe, configured to conduct a portion of the fuel in the gaseous state fuel from the combined fuel in the return flow path 50 to the disposal device 125. It shall be understood that the device 10 comprises one or more control units for the control of the valves, pumps, of the device 10. Preferably, a master control unit is used for the overall control of the operation of the device 10. While a master control unit is used, the device 10 may still comprise individual control units for specific functions, such as the return flow control unit 86 and the consumption flow control unit 96. In fig.1b is a further embodiment of a system 1 and a device 10 for cooling a fuel in a fuel tank 12 disclosed. The embodiment in fig.2b differs from the embodiment in fig.1a in that the device 10 comprise a first type fuel pump 34a and a second type fuel pump 34b. The first type fuel pump 34a is configured to provide a first pressure to the consumption flow path 60. In the disclosed embodiment, the first type fuel pump 34a is indicated located at the fuel tank. However, is shall be understood that alternative locations of the first type fuel pump 34a are possible as long as the consumption flow path 60 is set to the first pressure. The first type fuel pump 34a and the second type fuel pump 34b are configured to together provide a second pressure to the positive displacement flow path 30. In the discloses embodiment, the second type fuel pump 34b is located at the positive displacement flow path 30. However, is shall be understood that alternative locations of the second type fuel pump 34b are possible as long as the positive displacement flow path 30 is set to the second pressure. The first type fuel pump 34a and the second type fuel pump 34b are configured to be operated such that the second pressure is higher than the first pressure. Thereby, the efficiency of the device 10 is improved. The first type fuel pump 34a is designed to operate at the first pressure. The first type fuel pump 34a is for example a dynamic pump, such as a centrifugal type pump, or a positive displacement pump, such as a piston type pump or a screw type pump. The first type fuel pump 34a is preferably powered by an electric motor. The second type fuel pump 34b is designed to operate at the second pressure. The second type fuel pump 34b is preferably a positive displacement pump, such as a piston type pump or a screw type pump. The second type fuel pump 34b is preferably powered by an electric motor. According to an embodiment of the invention, the device 10 is configured to hold and conduct the fuel in the form of Ammonia. The first pressure is configured to be set to an interval of 1 to 10 bar, preferably 2 to 8 bar, by the first type fuel pump 34a. The second pressure is configured to be set to an interval of 70 to 90 bar, preferably 75 to 85 bar, by the combined operation of the first type fuel pump 34a and the second type fuel pump 34b. According to an embodiment of the invention, the device 10 is configured hold and conduct the fuel in the form of Liquid Natural Gas (LNG). The first pressure is configured to be set to an interval of 1 to 10 bar, preferably 2 to 8 bar, by the first type fuel pump 34a. The second pressure is configured to be set to an interval of 250 to 400 bar, preferably 300 to 350 bar, by the combined operation of the first type fuel pump 34a and the second type fuel pump 34b. In fig.2 is a flow chart of method for cooling a fuel in a fuel tank 12 according to an embodiment of the invention disclosed. The method is to be executed on the system 1 and the device 10 according to any of above embodiments of the invention. The method comprises, in a step 210, conducting the fuel in a liquid state or mainly liquid state from the fuel tank 12 by means of the positive displacement flow path 30 to the ejector 20. The flow of fuel in the liquid state or mainly liquid state is generating a flow of the fuel in a gaseous state from the fuel tank 12 by means of the forced flow path 40 to the ejector 20. The ejector 20 receives the fuel from the positive displacement flow path 30 and the forced flow path 40 and combines the two fuels into a combined fuel that flows from the ejector 20 to the fuel tank 12 by means of a return flow path 50. In a step 220, the method comprises conducting the fuel by means of the consumption flow path 60 from the fuel tank 12 to the consumption device 15 for consumption of the fuel. The fuel in the consumption flow path 60 is configured to be vaporized prior to being consumed by the consumption device 15. In a step 230, the method comprises conducting heat from the combined fuel in the return flow path 50 to the fuel in the consumption flow path 60. The heat is conducted by means of the heat exchanger 70 from the combined fuel in the return flow path 50 to the fuel in the consumption flow path 60. Thereby, the combined fuel in the return flow path 50 is cooled so that the pressure in the fuel tank 12 is reduced, and the fuel in the consumption flow path 60 is heated. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. For instance, adding a conduit from the positive displacement flow path 30 to the consumption flow path 60 between the heat exchanger 70 and the one or more heat exchangers 100 is an alternative embodiment of the invention.

Claims

Claims 1. A device (10) for cooling a fuel in a fuel tank (12), which fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank (12), wherein the fuel is configured to be vaporized prior to its consumption, wherein the device (10) comprises: - an ejector (20), - a positive displacement flow path (30) configured to conduct fuel in a liquid state from the fuel tank (12) to the ejector (20), - a forced flow path (40) configured to conduct fuel in a gaseous state from the fuel tank (12) to the ejector (20), - a return flow path (50) configured to receive fuel from the positive displacement flow path (30) and the forced flow path (40), and conduct a combined fuel to the fuel tank (12), and - a consumption flow path (60) configured to conduct fuel from the fuel tank (12) to a consumption device (15) for consumption of the fuel, wherein the device (10) further comprises: - a heat exchanger (70) configured to transfer heat from the return flow path (50) to the consumption flow path (60).

2. The device (10) according to claim 1, wherein the return flow path (50) comprises a return flow pressure regulating arrangement (80) configured to regulate a pressure of the combined fuel at the heat exchanger (70) such that the pressure is set to exceed a value or enters an interval in which a ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval.

3. The device (10) according to claim 2, wherein the return flow pressure regulating arrangement (80) comprises - a return flow sensor arrangement (84) configured to sense the ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on said ratio of the combined fuel in the return flow path (50), - a return flow pressure control valve (82) located at the return flow path (50)between the fuel tank (12) and the heat exchanger (70), wherein the device (10) further comprises; - a return flow control unit (86) configured to receive information from the return flow sensor arrangement (80) on the ratio between the liquid state fuel and the gaseous state fuel or the entity dependent on said ratio of the combined fuel in the return flow path (50), and on basis of the information control the return flow pressure control valve (82) such that the pressure is set to exceed the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval.

4. The device (10) according to claim 1, wherein the return flow path (50) comprises a return flow pressure regulating arrangement (80) configured to regulate a pressure of the combined fuel at the heat exchanger (70) such that the pressure is set to exceed a predetermined pressure value or enter a predetermined pressure interval.

5. The device (10) according to claim 4, wherein the return flow pressure regulating arrangement (80) comprises - a return flow sensor arrangement (84) configured to sense the pressure or an entity dependent on the pressure of the combined fuel in the return flow path (50), - a return flow pressure control valve (82) located at the return flow path (50) between the fuel tank (12) and the heat exchanger (70), wherein the device (10) further comprises; - a return flow control unit (86) configured to receive information from the return flow sensor arrangement (80) on the pressure or an entity dependent on the pressure of the combined fuel in the return flow path (50), and on basis of the information control the pressure return flow pressure control valve such that the pressure of the combined fuel at the heat exchanger (70) is set to exceed the predetermined pressure value or enters the predetermined pressure interval.

6. The device (10) according to any of claim 2-5, wherein the return flow sensor arrangement (80) comprises at least one of a pressure sensor, a liquid level sensor, and temperature sensor.

7. The device (10) according to any of the previous claims, wherein the positive displacement flow path (30) comprises at least one fuel pump (34) configured to generate a flow of the fuel in a liquid state from the fuel tank (12) to the ejector (20).

8. The device (10) according to any of the previous claims, wherein the consumption flow path (60) is configured to receive fuel from the positive displacement flow path (30).

9. The device (10) according to any of the previous claims, wherein the consumption flow path (60) is configured to be operated at a first pressure and the positive displacement flow path (30) is configured to be operated at a second pressure, wherein the second pressure is higher than the first pressure.

10. The device (10) according to claim 9, wherein the device (10) comprises a first type fuel pump (34a) and a second type fuel pump (34b), wherein the first type fuel pump (34a) is configured to pressurize the consumption flow path (60) to the first pressure, and wherein the first type fuel pump (34a) and the second type fuel pump (34b) together are configured to pressurize the positive displacement flow path (30) to the second pressure.

11. The device (10) according to any of claim 9-10, wherein the device (10) is configured hold and conduct the fuel in the form of Ammonia, wherein the first pressure is configured to be in the interval of 1 to 10 bar, preferably 2 to 8 bar, and wherein the second pressure is configured to be in the interval of 70 to 90 bar, preferably 75 to 85 bar.

12. The device (10) according to any of claim 9-10, wherein the device (10) is configured hold and conduct the fuel in the form of Liquid Natural Gas (LNG), wherein the first pressure is configured to be in the interval of 1 to 10 bar, preferably 2 to 8 bar, and wherein the second pressure is configured to be in the interval of 250 to 400 bar, preferably 300 to 350 bar.

13. The device (10) according to any of the previous claims, wherein the consumption flow path (60) comprises a consumption flow regulating arrangement (90) comprising a consumption flow control valve (92) configured to regulate the flow of the fuel from the fuel tank (12) to the heat exchanger (70) and a consumption flow sensor (94), wherein the device (10) comprises a consumption flow control unit (96) configured to control the consumption flow control valve based on information from the consumption flow sensor (94).

14. The device (10) according to any of the previous claims, wherein the device (10) comprises a liquid fuel outlet (32) configured to introduce fuel in the liquid state from the fuel tank (12) to the positive displacement flow path (30).

15. The device (10) according to any of the previous claims, wherein the device (10) comprises a gaseous fuel outlet (42) configured to introduce fuel in the gaseous state from the fuel tank (12) to the forced flow path (40).

16. The device (10) according to any of the previous claims, wherein the device (10) comprises a combined fuel inlet (52) configured to introduce the combined fuel from the return flow path (50) into the fuel tank (12).

17. The device (10) according to any of the previous claims, wherein the device (10) is configured hold and conduct the fuel selected from the group of Ammonia, Liquid Natural Gas (LNG), Liquefied Petroleum Gas (LPG), Ethylene, Propylene, Dimethyl Ether (DME), Butane, Isobutane.

18. A system (1) comprising a fuel tank (12), a device (10) according to any of claim 1-17, and a consumption device (15) for consumption of the fuel.

19. The system (1) according to claim 18, wherein the consumption device (15) is an engine.

20. A method for cooling a fuel in a fuel tank (12), which fuel is configured to be contained in both a liquid state and a gaseous state in the fuel tank (12), wherein the fuel is configured to be vaporized prior to its consumption, wherein the method comprises: - conducting the fuel in a liquid state from the fuel tank (12) by means of a positive displacement flow path (30) to an ejector (20), thereby generating a flow of the fuel in a gaseous state from the fuel tank (12) by means of a forced flow path (40) to the ejector (20), which results in a flow of a combined fuel by means of the return flow path (50) from the ejector (20) to the fuel tank (12), - conducting the fuel by means of a consumption flow path (60) from the fuel tank (12) to a consumption device (15) for consumption of the fuel, and - conducting heat from the combined fuel in the return flow path (50) to the fuel in the consumption flow path (60).

21. The method according to claim 20, wherein the method further comprises: - regulating the pressure of the combined fuel in the return flow path (50) at the heat exchanger (70) to exceed a value or enters a pressure interval in which a ratio between the liquid state fuel and the gaseous state fuel exceeds a predetermined value or enters a predetermined interval.

22. The method according to claim 21, wherein the method further comprises: - receiving information on the ratio between the liquid state fuel and the gaseous state fuel or an entity dependent on said ratio of the combined fuel in the return flow path (50),- controlling the pressure in the return flow path (50) at the heat exchanger (70) on basis of said information such that the pressure is set to the value or enter the interval in which the ratio between the liquid state fuel and the gaseous state fuel exceeds the predetermined value or enters the predetermined interval.

23. The method according to claim 20, wherein the method further comprises: - regulating the pressure of the combined fuel in the return flow path (50) at the heat exchanger (70) such that the pressure exceeds a predetermined value or enters a predetermined pressure interval.

24. The method according to claim 23, wherein the method further comprises: - receiving information on a pressure of the combined fuel in the return flow path (50) at the heat exchanger (70), and - controlling the pressure in the return flow path (50) at the heat exchanger (70) on basis of the information such that pressure is set to exceed a predetermined value or enters a predetermined interval.

25. The method according to any of claim 20-24, wherein the method further comprises: - receiving information on a pressure of the fuel in the consumption flow path (60) at the heat exchanger (70), and - regulating a pressure of the fuel in the consumption flow path (60) such that the pressure at the heat exchanger (70) is set to exceed a predetermined pressure value or enters a predetermined pressure interval.

26. The method according to any of claim 20-25, wherein the method further comprises: - pressurizing the consumption flow path (60) to a first pressure, and - pressurizing the positive displacement flow path (30) to a second pressure, wherein the second pressure is higher than the first pressure.

27. The method according to claim 26, wherein the fuel in the form of Ammonia, and the first pressure is in the interval of 1 to 10 bar, preferably 2 to 8 bar, and the second pressure is in the interval of 70 to 90 bar, preferably 75 to 85 bar.

28. The method according to claim 26, wherein the fuel in the form of Liquid Natural Gas (LNG), and the first pressure is in the interval of 1 to 10 bar, preferably 2 to 8 bar, and the second pressure is in the interval of 250 to 400 bar, preferably 300 to 350 bar.

29. Use of a device (10) according to any of claim 1-17.

30. Use of a system (1) according to any of claim 18-19.

Images