Patent Description:
More specifically the present invention relates to a fuel tank arrangement in a liquid hydrogen fuel supply system for storing and providing hydrogen for a gas consumer, the system comprising:.

More specifically the method of present invention relates to a method in filling a liquid hydrogen fuel supply system for storing and providing liquid hydrogen for a gas consumer, the method comprising steps of:.

Natural gas as a fuel for internal combustion engines in marine vessels, power plants and such, has become more common because of the environmental reasons since the combustion results are less harmful than for example those resulted in combustion of heavy or light fuel oil. However, also gaseous fossil fuels are generally harmful to the environment and therefore any leakage to the atmosphere is undesired. That is why all equipment for handling and regulating gas fuel is subjected to stringent safety regulations. In a transformation from fossil fuels to renewable fuels one possible next step is hydrogen. The same or even more demanding regulations apply if the gaseous fuel is hydrogen because it has lower boiling temperature than the liquified natural gas (LNG). Hydrogen has also small molecular size making it prone to leak.

Hydrogen is one of the most potential alternative fuels for future needs. Hydrogen can be used in a mixture of fuels in an internal combustion piston engine. For example, with LNG it can be used up to a certain share of the total fuel mixture. Alternatively, hydrogen can be used as the only fuel for a fuel cell. A fuel cell is an electrochemical cell that converts the chemical energy of a fuel, such as hydrogen and an oxidizing agent into electricity through a pair of redox reactions. Fuel cell systems are different from most batteries in requiring a continuous source of fuel and oxygen to sustain the chemical reaction. In that sense the requirements of hydrogen based power systems are closer to the LNG-fuel systems than a battery-based system.

However, for various reasons both the tank and the tank connection space used for storing and handling liquid hydrogen require specific attention. Firstly, hydrogen storage and processing in general imply high risk of fire and explosion due to, on the one hand, the wide range of mixture giving explosive atmosphere and, on the other hand, the low ignition energy typical to hydrogen. Secondly, the detection of hydrogen is relatively slow.

For reference, in publication <CIT> it is presented a fuel tank arrangement of a marine vessel, the tank arrangement comprising a liquid hydrogen fuel tank, a tank connection space arranged in communication with the liquid hydrogen fuel tank, the tank connection space being provided with a vent mast having a lower end and an upper end, and an interior, the interior of the vent mast forming a ventilation outlet line for discharging gas from the tank connection space, an emergency pressure relief valve coupled via a safety valve line to the gas space of the fuel tank, wherein a first hydrogen outlet line provided in the vent mast is separate from the ventilation outlet line, the first hydrogen outlet line extending from the lower end of the vent mast to the upper end thereof and being arranged in flow communication with the emergency pressure relief valve.

In publication <CIT> it is presented a method for operating a LNG fuelled marine vessel, which marine vessel comprises a bunker station comprising an inlet pipe to which a source of LNG is arranged to be connected, a LNG storage tank connected to the bunker station and a LNG fuelled power plant, in which method in connection with a bunkering operation the marine vessel is supplied with LNG by connecting the source of LNG to a bunkering line of the marine vessel through the inlet pipe of the bunker station and subsequently supplying LNG to the LNG storage tank through the bunkering line. The bunkering line is cooled down to a temperature level corresponding to the temperature level of the LNG by re-circulating LNG from a lower part of the LNG storage tank to the bunkering line and back to the LNG storage tank by way of the bunkering line before the marine vessel arrives at a bunkering facility.

A basic configuration for fuel supply for a hydrogen based power generating system would be that the fuel consumption units (such as a number of interconnected fuel cells) are connected to a tank that can be filled from outside. The system can be for example in a marine application where the fuel cells are the power source for a marine vessel, the tank is in the vessel and the fuel filling system is in a harbour or in a truck or in a bunkering system. It may also be that the fuel consumption units are arranged to form a land-based power plant and the fuel is delivered by trucks or trains to the power plant. The same principle can even be applied to normal passenger cars, busses or cargo trucks.

One of aspects that needs to be taken in to account is the very low boiling temperature of liquified gaseous fuels. With LNG that is -<NUM> and that affects in design of the LNG fuel supply system. As normal atmosphere temperatures are significantly above the boiling temperature of LNG and meaning that the liquid fuel would boil and transit to gas phase very quickly when in connection with any non-cryogenic components such as fuel supply system parts, pipes, valves, etc. in atmosphere temperature. For economical and practical reasons the cryogenic conditions are limited to the minimum, such as to the tank and to the proximity of the tank, such as to a tank connection space. The tank is surrounded by valves so that any connection such as a fuel supply line to or from the tank is equipped with a valve. After filling up the tank it is a mandatory practice to make the fuel supply system inert. These fuel supply systems may be especially long in case of marine vessels, where the fuel supply pipeline can be tens or even hundreds of meters. In case of LNG this inerting is done with nitrogen. The nitrogen gas phase temperatures are suitable for the purpose, because nitrogen is condensing at -<NUM> C and freezing at -<NUM> C. This means that nitrogen remains in gas phase if it is supplied to the pipeline after LNG. However, the same method and substance cannot be applied to the hydrogen fuel supply system. One of the key differences between liquid hydrogen and LNG is the boiling temperature of the liquid, and with hydrogen it is -<NUM>,<NUM>. This means that if nitrogen would be fed to the pipeline after liquified hydrogen, it would condensate or even freeze to the pipelines and most likely start causing problems.

An object of the invention is to provide an arrangement in a liquid hydrogen fuel supply system connectable to a bunkering station for providing the liquid hydrogen to the system. Another object of the invention is to provide a method in a liquid hydrogen fuel supply system connectable to a bunkering station for providing the liquid hydrogen to the system. In both arrangement and in method the performance is considerably improved compared to the prior art solutions.

Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

According to an embodiment of the invention it is provided a fuel tank arrangement in a liquid hydrogen fuel supply system for storing and providing hydrogen for a gas consumer, the system comprising:.

This provides an arrangement in which performance is considerably improved and the inerting operation can be done efficiently and safely. It requires a special arrangement of components suitable for these very demanding low temperature cryogenic conditions. However, the arrangement utilizes to large extent features that are already required for other purposes and the additional elements are relatively small in number.

According to an embodiment the arrangement is utilized by a method in filling a liquid hydrogen fuel supply system for storing and providing liquid hydrogen for a gas consumer, the method comprising steps of:.

According to an embodiment of the invention the source of gaseous hydrogen is a device for increasing pressure and temperature of gaseous hydrogen and it is connected to or supplied by gaseous or liquid hydrogen in the tank. Thus, the same fuel that has been filled for consumption is the media for flushing and it is first taken from the tank to a device for increasing the pressure and the temperature and then lead for flushing and warming up the inlet line. The flushing gas may be taken from the gas space of the tank. A part of the liquid hydrogen in the tank evaporates and forms so called boil off gas. This is already in the gas phase and a step for vaporising the liquid to gas phase can be avoided. In the flushing operation the warmed gas will be returned to the tank again. Using evaporated and heated liquid hydrogen for the fuel gas flushing operation, and re-introducing it as gas into the tank, increases pressure in the tank more than using heated boil off gas from the tank for the flushing operation. Thus, using boil off gas and then just re-introducing heated gas into the tank is more economical alternative, since the step of evaporating liquid hydrogen is avoided. However, for flushing the pressure of the flushing gas needs to be raised anyway by suitable means. Otherwise, the pressure in both inlet line and in the fuel gas flush media line would be the same and no flushing would happen.

There are a couple of alternatives for the pressure and temperature increase of hydrogen and the used heater/evaporator for the flushing operation. One is that the source of gaseous hydrogen is a main gas evaporator of the tank arrangement using tank boil off gas or liquid phase hydrogen. The main gas evaporator is used for evaporating and heating liquid gas for in normal operation when fuel from the tank arrangement is used by a gas consumer. Other alternative is that the source of pressurized gaseous hydrogen is a pressure build-up evaporator. The pressure build-up evaporator is used in a pressurized tank arrangement, which is an option for a pump operated tank arrangement, for increasing and maintaining sufficient pressure in the tank for a gas consumer in operation. Still other possible source of hydrogen for the flushing operation is a pressure increase device, being a pump, pressure accumulator or similar. This choice source of gaseous hydrogen depends on the actual configuration of the system, many configurations are possible.

According to an embodiment of the method the inlet line safety procedure is two step procedure. First the fuel gas flush pushes any remaining liquid hydrogen to the tank and evaporates possible small residuals of liquid hydrogen and warms up the inlet line. The next step is the inert gas flush that replaces the fuel gas in the inlet line by pushing it to the tank. For both steps suitable flush volumes and pressures are selected by the actual configuration, by inlet line diameter and length. The flush pressure and flow velocity need to be adequate to move the media in front of the flush media.

According to an embodiment of the invention the inlet line is provided with a temperature sensor (or a number of sensors) for determining the temperature of the inlet line. This feature enables the temperature monitoring of the inlet line. For the fuel gas flushing an amount of liquid hydrogen has been boiled off or is evaporated to gas phase and warmed up to a predetermined temperature above Tn, wherein Tn is the condensing temperature of the inert gas. During fuel gas flush the temperature of the inlet line is being monitored and after the temperature of the inlet line is determined to be above Tn, the fuel gas flush media line is closed and the flushing with the inert gas can be initiated. It is useful for an operator to know if the inlet line temperature is so low that the inert gas would condensate or freeze. In other words, the fuel gas flushing is advantageously continued until the inlet line temperature has risen first above the freezing temperature of the inert gas and then above the condensing temperature of the inert gas. Only after that it is safe to lead the inert gas to the inlet line and flush it to inert condition, to make the inlet line being without of danger of containing inflammable or explosive amount of fuel residuals. The completion of inert gas flush may be determined for example by measuring the concentration of the inert gas in the tank end of the inlet line. Completion of the inerting phase can also be confirmed by considering that a certain amount of volume exchanges has been done, e.g. the amount of nitrogen used for flushing is for example <NUM> times the volume of inlet line, meaning that sufficient flushing is done and the line can be considered inerted. Most suitably the inert gas is nitrogen because it is cheaper than other inert gases, so operational costs for the power generating system operator are kept low. Some other alternatives such as argon or helium may also be considered.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

<FIG> depicts schematically a fuel tank arrangement in a liquid hydrogen fuel supply system <NUM> for storing and providing hydrogen for a gas consumer <NUM>, the system comprising:.

and a second end of which is connected to a source of gaseous hydrogen <NUM>, for feeding gaseous hydrogen to the inlet line <NUM> for performing a first flushing of the inlet line <NUM>.

According to an embodiment the arrangement is utilized by a method in filling a liquid hydrogen fuel supply system <NUM> for storing and providing liquid hydrogen for a gas consumer <NUM>, the method comprising steps of:.

In <FIG> the liquid hydrogen fuel supply system <NUM> is arranged so that the source of gaseous hydrogen <NUM> is a device for increasing pressure and temperature of gaseous hydrogen and it is connected to or supplied by gaseous or liquid hydrogen in the tank <NUM>. Concerning the source of gaseous hydrogen <NUM>, the numeral <NUM> refers schematically in <FIG> to an initial spot in the fuel gas flush line <NUM> where the actual devices outlet may be connected. As in <FIG>, the numeral <NUM> points to an intersection where both options, a main gas evaporator <NUM> or a pressure built-up evaporator <NUM> that evaporates an amount of hydrogen may be selectably connected. With said evaporator devices an amount of liquid hydrogen is evaporated to gas phase and warmed up (or only warmed up if the hydrogen is already in gas phase) to a predetermined temperature above Tn, wherein Tn is the condensing temperature of the inert gas. Evaporation and subsequent heating can be powered for example by a source of external heat, such as the gas consumer cooling system, as illustrated in <FIG> with references for the heating fluid heat in (H_in) and heat out (H_out). It is also possible to use electric heating for this purpose. An electric heater may be integrated into the evaporator providing heat there directly, or into the heating fluid circuit providing additional heating into the fluid before it enters the evaporator. Hereby the added electric heater solves a problem that sufficient heat may not be available in the heating fluid at the moment a bunkering operation is completed, and the fuel line should be flushed and inerted.

In fuel gas flushing step warm gaseous hydrogen is supplied to the inlet line <NUM> downstream of the first valve <NUM>, the gaseous hydrogen is flushing the inlet line <NUM> and simultaneously warming up the inlet line <NUM>. The fuel gas flush pushes any remaining liquid hydrogen in the inlet line <NUM> to the tank <NUM> and evaporates possible small residuals of liquid hydrogen. An operator of the system can select the inlet line <NUM> end to a gas space 11a or liquid space 11b by opening and closing suitable valves 11a1 and 11b1. For fuel gas flushing it is relevant that the portion of pipe between valve <NUM> and valve <NUM> is flushed, to push the remaining liquid hydrogen in the inlet line <NUM> to the tank <NUM>. It is suggested to open only valve 11a1, because the media to be flushed consist of hydrogen both in liquid phase and in gas phase. It is not convenient to do this flushing leading to the liquid part in the tank 11b, but rather to flush towards the line leading to the gaseous part of the tank 11a. In the end of this step the inlet line temperature is above condensing temperature (Tn) of the inert gas and it is filled with fuel gas, gaseous hydrogen. The inlet line <NUM> is provided with a temperature sensor <NUM> or a number of temperature sensors along the inlet line <NUM> for determining the temperature of the inlet line <NUM>. Advantageously also the fuel gas flush line <NUM> is equipped with a temperature sensor <NUM>. With the temperature information it is possible to determine the status of the inlet line <NUM> if it is in safe condition and ready for the next process step being the inert gas flushing. When the temperature of the inlet line <NUM> is being monitored and after the temperature of the inlet line <NUM> is determined to be above Tn, the fuel gas flush media line <NUM> is closed and the flushing with the inert gas can be initiated.

In the inert gas flush the inlet line <NUM> is supplied with an inert gas via an inert gas flush media line <NUM> controllably connected to the inlet line <NUM> downstream of the first valve <NUM>, the supplied inert gas flushing the hydrogen away from the inlet line <NUM> into the tank <NUM>. Here the inert gas flush replaces the fuel gas in the inlet line <NUM> by pushing it to the tank <NUM>. Therefore, the pressure and flow rate of the inert gas need to be selected so that the flushing may happen.

It is presented one embodiment of liquid hydrogen fuel supply system <NUM> for storing and providing hydrogen for a gas consumer <NUM>. During normal operation of the system gas is provided from the insulated tank <NUM> via outlet line <NUM> to one of the evaporators, either to the pressure build-up evaporator <NUM> and back to the tank <NUM>, or the main gas evaporator <NUM> and then further to the gas consumer <NUM> such as an engine, fuel cell, etc.. The pressure build-up evaporator is used for evaporating liquefied gas and feeding it back to the tank in order to maintain a pressure in the tank that is sufficiently high for the system operation. The pressure build-up evaporator is in operation based on need for increasing the pressure in the tank.

In the system according to <FIG> the generation of the fuel flush gas can be made in several ways, here described with no particular preference order. A first option is to use the pressure build-up evaporator. According to this option, the outlet line <NUM> valve <NUM> from the tank <NUM> is opened, and valve <NUM> for the line leading to the main gas evaporator <NUM> is closed. Heating fluid is arranged to flow through the pressure build-up evaporator <NUM>. Valves <NUM> and <NUM> are open enabling circulation through the pressure build-up evaporator <NUM>, which evaporates the liquid hydrogen. Valves <NUM>, <NUM> and <NUM> being closed, and valves <NUM> and <NUM> open, the evaporated gas flows to the fuel gas flush media line <NUM>. With valves <NUM> and <NUM> open, and valve <NUM> closed, the fuel flush gas flushes the inlet line <NUM> towards the tank. A second option is to use the main gas evaporator <NUM> with liquid hydrogen from the tank <NUM>. As a difference to option <NUM>, valve <NUM> for the line leading to the main gas evaporator <NUM> is opened, while valve <NUM> enabling circulation through the pressure build-up evaporator <NUM> is closed. Heating fluid is now arranged to flow through the main gas evaporator <NUM>. With valve <NUM> leading to gas consumers <NUM> closed, and valves <NUM> and <NUM> open and <NUM> closed, the fuel flush gas is generated to be led to line <NUM> the same way as in option <NUM>. A third option is to use gaseous hydrogen, so called boil off gas from the tank <NUM>. By opening valves <NUM> and <NUM>, closing valves <NUM>, <NUM> and <NUM>, gaseous hydrogen is led to the main gas evaporator <NUM> for pressure and temperature increase. With valve <NUM> leading to gas consumers <NUM> closed, and valves <NUM> and <NUM> open and <NUM> closed, the fuel flush gas is generated to be led to line <NUM> the same way as in option <NUM> and option <NUM>.

For a person skilled in the art, it is clear that in some case in the embodiment of <FIG>, both the build-up evaporator <NUM> and main gas evaporator <NUM> could be used as parallel evaporators for generating the fuel flush gas.

The fuel tank arrangement in <FIG> is provided with a tank connection space <NUM> for comparting connections to and from the tank <NUM>. The fuel supply system is equipped with a number of control valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> shown with standard symbol for valves in <FIG> and <FIG>. A person familiar with the art should understand which valve need to be closed and which valve need to be open or regulated to perform the function of the system.

In <FIG> it is presented a fuel tank arrangement in a liquid hydrogen fuel supply system <NUM> for storing and providing hydrogen for a gas consumer <NUM>, the system comprising:.

and a second end of which is connected to a source of gaseous hydrogen <NUM>, for feeding gaseous hydrogen to the inlet line <NUM> for performing a first flushing of the inlet line <NUM>. This embodiment of the system <NUM> differs from what has been explained above on <FIG> so that the fuel supply system <NUM> utilizes a fuel pump <NUM> for pressuring up the fuel for the main gas evaporator <NUM> and therefore the piping is slightly different compared to <FIG> because the pressure build-up evaporator is missing. Otherwise, the features and function remain the same as has been explained above in connection with <FIG>.

In the system according to <FIG> the generation of the fuel flush gas can be made in a following way. First the outlet line <NUM> valve <NUM> from the tank <NUM> is opened, a valve <NUM> closed and the fuel pump <NUM> is utilized to lead the fuel towards opened valve <NUM> and to the line leading to the main gas evaporator <NUM>. Heating fluid is arranged to flow through the main gas evaporator <NUM>, which evaporates and heats the liquid hydrogen. Valve <NUM> leading to gas consumers <NUM> being closed, and valves <NUM> and <NUM> open, the evaporated gas flows to the fuel gas flush media line <NUM>. With valves <NUM> and <NUM> open, and valve <NUM> closed, the fuel flush gas flushes the inlet line <NUM> towards the tank <NUM>. Also with the embodiment of <FIG> it is possible to use boil off gas from the tank. Then the valves <NUM> and <NUM> are open while valve <NUM> is closed, no fuel pump <NUM> is utilized. Otherwise, the features and function remain the same as has been explained above in connection with <FIG>.

Claim 1:
A fuel tank arrangement in a liquid hydrogen fuel supply system (<NUM>) for storing and providing hydrogen for a gas consumer (<NUM>), the system comprising:
- an inlet line (<NUM>) for providing fuel into a tank (<NUM>),
- the inlet line (<NUM>) having a first valve (<NUM>) in the first end and a second valve (<NUM>) in the tank end,
- the inlet line (<NUM>) is provided with an inert gas flush media line (<NUM>), the first end of which is connected to the inlet line (<NUM>) downstream of the first valve (<NUM>), and a second end of which is controllably connected to a source of inert gas (<NUM>) for performing an inert gas flushing of the inlet line (<NUM>),
characterized in that the system further comprises:
- the inlet line (<NUM>) being provided with a fuel gas flush media line (<NUM>), the first end of which is controllably connected to the inlet line (<NUM>) downstream of the first valve (<NUM>),
and a second end of which is connected to a source of gaseous hydrogen (<NUM>), for feeding gaseous hydrogen to the inlet line (<NUM>) for performing a first flushing of the inlet line (<NUM>).