Arrangement for transferring liquid hydrogen

Abstract

An arrangement for transferring liquid hydrogen from a first storage container (1) to a second storage container (2) is described, in which the storage container to be filled can be filled with a filling quantity of more than 200 kg at filling rates of more than 1 tonne per hour, for which only a filling line but no return line is required.

Description

[0001] The invention relates to an arrangement for transferring liquid hydrogen from a first storage container to a second storage container, wherein the two storage containers can be connected to each other by means of a connecting line, and a pump and a filling valve are provided in the connecting line.

[0002] The first storage container will subsequently be referred to as the donor and the second storage container as the receiver.

[0003] Typical arrangements for transferring liquid hydrogen from a donor to a receiver are used, for example, in filling liquid hydrogen storage tanks of aircraft, ships, locomotives, or trucks. In such applications, storage containers with a capacity of more than 200 kg must be filled at rates exceeding 1 tonne per hour.

[0004] According to the current state of the art, the transfer of liquid hydrogen from a donor to a receiver is achieved by connecting the two storage containers via a connecting line. This connecting line can be a rigid pipe, a flexible hose, or a combination of both. In applications where the two storage containers need to be separated, the connecting line is equipped with a suitable coupling. When connecting the two storage containers, purging steps may be necessary to clean the line and coupling. Furthermore, measuring devices such as flow meters, orifices, etc., can be integrated into the connecting line.

[0005] The connecting line must include at least one pump and a filling valve. A piston liquid hydrogen pump or a centrifugal liquid hydrogen pump (centrifugal pump) is typically used. In this design, the pump generates a pressure differential necessary for liquid transfer. However, the pressure in the receiver can be either higher or lower than the pressure in the dispenser, depending on pressure losses in the connecting line and the setting of the filling valve. For the method considered here, the relevant case is when the pressure in the receiver is higher than in the dispenser. In this case, the two storage containers are connected on the gas side using additional, appropriate lines and couplings.This allows the gas displaced by the liquid, as well as any boil-off gas produced, to be returned to the dispenser in the receiver. This at least partially prevents the venting of the boil-off gas and the displaced gas, thus reducing the corresponding hydrogen losses. If recirculation of this gas is not possible, it must be used for another purpose and / or disposed of safely, e.g., by flaring.

[0006] The dispenser typically has a pressure regulating system, as described below, which serves to maintain the desired pressure within the dispenser. Boil-off gas returned to the dispenser can relieve the strain on this pressure regulating system.

[0007] To achieve a sufficient net positive stagnation head (NPSHA) at the pump inlet—the NPSHA must be greater than or equal to the required net positive stagnation head (NPSHR)—the liquid hydrogen in the dispenser may need to be conditioned. Various solutions can be implemented to achieve this. For example, the dispenser can be installed at a higher elevation relative to the pump. In this way, the hydrostatic pressure build-up helps to achieve the required liquid condition at the pump inlet. However, due to the low gravimetric density of liquid hydrogen, additional measures are usually necessary to ensure a sufficient NPSHA value on the pump suction side and thus prevent cavitation.

[0008] The liquid hydrogen in the dispenser can be conditioned using a pressure regulating system. This system can be designed in various ways. Often, a relatively simple pressure regulating system is used, consisting essentially of a valve and an ambient vaporizer, and functioning as follows: Extremely cold hydrogen is drawn from the bottom of the dispenser and fed to the pressure regulating system. The required amount of liquid is set via the valve in the pressure regulating system. The temperature difference between the relatively warm ambient air and the hydrogen is used to vaporize the liquid into a gas; the gaseous hydrogen may be superheated in this process. This gas is then fed into the gas chamber of the dispenser. Due to the larger volume and higher energy of the incoming gas compared to the extracted liquid, and due to the constant dispenser volume, the pressure in the dispenser increases.In this way, the pressure in the dispenser can be regulated using the pressure control valve. Alternatively or additionally, rapid pressurization of the dispenser, and thus conditioning of the liquid hydrogen, can be achieved by an external pressurized gas source connected to the dispenser via a line and a control valve.

[0009] Managing the aforementioned displaced gas and boil-off gas requires considerable technical effort. This is true even if the boil-off gas is not intended to be returned to the donor and is only to be disposed of. If the boil-off gas is returned from the receiver to the donor via a second connecting line, corresponding hardware components such as lines, couplings, controls, etc., are required. Overall, this results in a negative impact on the economic viability of the entire liquid hydrogen transfer system.

[0010] A known method exists for transferring liquid hydrogen from a first storage container to a second storage container, requiring only a single connecting line between the donor and receiver. This method is used for receivers with a filling volume of less than 100 kg of liquid hydrogen. A piston pump is employed in this system. This principle is referred to as a subcooled liquid hydrogen pumping system. The previously described procedures can be used to condition the liquid hydrogen at the piston pump inlet. The piston pump reduces the pressure of the liquid hydrogen to less than 16 bar. Thermodynamically, the liquid hydrogen at the pump outlet is in a subcooled state and, if the pressure exceeds 13 bar, in a supercritical state. The subcooled liquid hydrogen is then injected into the gas and / or liquid space of the receiver.Due to the supercooled state of the hydrogen, the boil-off gas and the vapor phase can recondense in the receiver, resulting in a relatively slow increase in the receiver's internal pressure. Filling is stopped when the maximum permissible pressure is reached. The previously described second connecting line for the return of gaseous hydrogen during refueling is therefore unnecessary with this method.

[0011] The required degree of subcooling of the liquid entering the receiver is defined by a) the design of the transfer line (geometry, materials), b) the amount of warm gaseous hydrogen in the receiver, and c) the design and thermal mass of the receiver. In existing applications, these parameters are chosen such that a relatively high degree of subcooling of the hydrogen to be pumped and a corresponding maximum receiver pressure of up to 16 bar are required. The necessary pressure build-up can only be achieved using a piston pump.

[0012] The object of the present invention is to provide a generic arrangement for transferring liquid hydrogen from a first storage container (donor) to a second storage container (receiver) that enables operation at lower pressures and the filling of storage containers with a capacity of more than 200 kg at filling rates of more than 1 tonne per hour. As explained above, such specifications are necessary or desirable for filling liquid hydrogen storage tanks of aircraft, ships, locomotives, trucks, etc.

[0013] To solve this problem, an arrangement for transferring liquid hydrogen from a first storage container to a second storage container is described, characterized in that the pump is a centrifugal pump, the centrifugal pump has an efficiency of at least 30%, the centrifugal pump is designed in such a way that it allows subcooling of the liquid hydrogen at the pump outlet, the connecting line is designed in such a way that subcooling of the liquid hydrogen is present at the outlet of the connecting line, the second storage tank can withstand an internal pressure of up to 10 bar, means for adjusting the temperature of the liquid hydrogen at the pump inlet are provided, wherein the temperature of the liquid hydrogen at the pump inlet is adjusted in such a way that the maximum permissible internal pressure of the second storage tank is not exceeded during the transfer of the liquid hydrogen, and means for sensing the internal pressure of the second storage tank are provided, wherein the transfer process is terminated when the maximum permissible internal pressure of the second storage tank is reached.

[0014] Further advantageous embodiments of the arrangement according to the invention for transferring liquid hydrogen from a first storage container to a second storage container are characterized in that The first storage tank is assigned a pressure control system for conditioning the liquid hydrogen in the first storage tank, at least one measuring device, preferably a flow meter, is arranged in the connecting line, the connecting line has a coupling, the second storage tank can withstand an internal pressure of at least 5 bar, the second storage tank has a capacity of at least 200 kg of hydrogen, the second storage tank consists of one or more separate containers, each having common insulation or its own insulation, and means are provided for feeding the subcooled liquid hydrogen into the second storage tank, improving the mixing of the hydrogen fed into the storage tank and the hydrogen already present in the storage tank.

[0015] The arrangement according to the invention now makes it possible to fill storage containers with a capacity of more than 200 kg at filling rates of more than 1 ton per hour, requiring only a single connecting line between the storage containers or the dispenser and the receiver. A centrifugal pump must be used, as the piston pumps used previously are limited in their delivery rate. Centrifugal pumps enable a high flow rate, allowing the desired filling rates to be achieved. The centrifugal pump must have an efficiency of at least 30% and must be designed to ensure sufficient subcooling of the liquid hydrogen at the pump outlet. Furthermore, the second storage container or receiver must be designed to withstand an internal pressure of up to 10 bar, preferably up to 5 bar.Furthermore, means for adjusting the temperature of the liquid hydrogen at the pump inlet are to be provided. These means are used to adjust the temperature of the liquid hydrogen at the pump inlet such that the maximum permissible internal pressure of the receiver is not exceeded during the transfer of the liquid hydrogen. The arrangement according to the invention also includes means for sensing the internal pressure of the receiver, whereby the transfer process is terminated when the maximum permissible internal pressure of the receiver is reached. In this way, excess expansion, displacement, and boil-off gas in the receiver can be recondensed by the incoming supercooled hydrogen, while the pressure remains below the design pressure of the receiver. Therefore, the previously required second line, which serves to extract gaseous hydrogen from the receiver during refueling and, if necessary, return the hydrogen to the dispenser, is no longer required.

[0016] The arrangement according to the invention, as well as further advantageous embodiments thereof, are described below with reference to the one in the Figure The illustrated embodiment is explained in more detail.

[0017] This shows the arrangement according to the invention with two storage containers, a dispenser 1 and a receiver 2. The two storage containers are connected to each other via a connecting line 3, 14. A coupling 5 may be provided for this purpose. A centrifugal pump 13 and a filling valve V are arranged in the connecting line 3, 14. The line section 3 connects the dispenser 1 to the suction side of the centrifugal pump 13, while the pressure side of the centrifugal pump 13 is connected to the receiver 2 via the line section 14. Measuring devices, such as flow meters, orifices, etc., may optionally be provided in the connecting line. Liquid hydrogen from the dispenser 1 is directed to the pump suction side, whereby its pressure decreases due to friction losses in the line section 3. A pressure regulating system 7 is associated with the dispenser 1, to which liquid hydrogen 1b is supplied from the dispenser 1 via line 10.The hydrogen vaporized in the pressure regulating system 7 is fed to the gas chamber 1a of the dispenser 1 via line 11. The pressure regulating system 7 conditions the liquid hydrogen in the dispenser 1 so that it is completely liquid at the pump inlet.

[0018] The centrifugal pump 13 increases the pressure of the liquid hydrogen to up to 10 bar. Due to the efficiency of the centrifugal pump 13, which is at least 30 percent, the hydrogen is thermodynamically supercooled on the pressure side of the pump and is fed to the receiver 2. Friction losses in the line section 14 cause the pressure of the hydrogen to drop. The pressure increase in the centrifugal pump 13 and its efficiency are sufficient to ensure that the hydrogen is sufficiently supercooled upon entering the receiver 2. Because of the supercooled state of the hydrogen, the hydrogen gas can condense back into liquid form in the receiver 2, thus maintaining the pressure in the receiver 2 below its maximum design pressure.The temperature at the pump inlet is conditioned, and the diameter, length, and thermal insulation of the connecting lines are selected to ensure that the maximum pressure in receiver 2 is not reached during the refueling process. As the refueling process nears completion, the pressure in receiver 2 rises sharply. This indicates the end of the refueling process. Once a predetermined maximum pressure of 5 bar or 10 bar is reached in receiver 2, valve V3, which is connected to a pressure gauge via control line 6, closes automatically to terminate the refueling process.

[0019] The required degree of subcooling of the hydrogen flowing into receiver 2 is determined by the connecting line, the amount of warm gaseous hydrogen in receiver 2, and the thermal mass of the receiver. Due to the receiver's charging or storage capacity, preferably greater than 200 kg, the influence of the receiver's thermal mass is reduced relative to the influence of the amount of warm gaseous hydrogen in the receiver compared to the prior art. Therefore, a relatively low degree of subcooling at the outlet of the centrifugal pump 13 and a maximum pressure of up to 5 bar or 10 bar in receiver 2 are sufficient.

[0020] The arrangement according to the invention for transferring liquid hydrogen from a first storage container to a second storage container enables the comparatively rapid refueling of larger quantities of liquid hydrogen using only one connecting line between the two storage containers. Furthermore, all processes before and after refueling, such as coupling, purging, cooling, etc., only need to be carried out for one connecting line, thereby reducing the required time, ideally by half. Under normal operating conditions, no gaseous hydrogen needs to be extracted from and processed by the receiver 2. This significantly simplifies the required refueling infrastructure.Furthermore, the automatic stopping of the refueling process when the maximum permissible pressure in the receiver is reached is a faster, simpler and safer process compared to the use of conventional flow meters or level indicators to indicate the end of the refueling process.

Claims

1. Arrangement for transferring liquid hydrogen from a first storage container to a second storage container, wherein - the two storage containers (1, 2) can be connected to each other by means of a connecting line (3, 14), and - a pump (13) and a filling valve (V3) are provided in the connecting line (3, 14), characterized by the fact that- the pump is a centrifugal pump (13), - the centrifugal pump (13) has an efficiency of at least 30%, - the centrifugal pump (13) is designed such that it allows subcooling of the liquid hydrogen at the pump outlet, - the connecting line (3, 14) is designed such that subcooling of the liquid hydrogen occurs at the outlet of the connecting line (3, 14), - the second storage tank (2) can withstand an internal pressure of up to 10 bar, - means for adjusting the temperature of the liquid hydrogen at the pump inlet (13) are provided, wherein the temperature of the liquid hydrogen at the pump inlet (13) is adjusted such that the maximum permissible internal pressure of the second storage tank (2) is not exceeded during the transfer of the liquid hydrogen, and - means for measuring the internal pressure of the second storage tank (2) are provided.the transfer process is terminated when the maximum permissible internal pressure of the second storage container (2) is reached.

2. Arrangement according to claim 1, characterized by the fact that The first storage tank (1) is associated with a pressure control system (7) which serves to condition the liquid hydrogen in the first storage tank (1).

3. Arrangement according to claim 1 or 2, characterized by the fact that at least one measuring device, preferably a flow meter, is arranged in the connecting line (3, 14).

4. Arrangement according to one of the preceding claims, characterized by the fact that the connecting line (3, 14) has a coupling (5).

5. Arrangement according to one of the preceding claims, characterized by the fact that the second storage container (2) withstands an internal pressure of at least 5 bar.

6. Arrangement according to one of the preceding claims, characterized by the fact that the second storage container (2) has a capacity of at least 200 kg of hydrogen.

7. Arrangement according to one of the preceding claims, characterized by the fact that the second storage container (2) consists of one or more separate containers, which have a common insulation or each have its own insulation.

8. Arrangement according to one of the preceding claims, characterized by the fact that Means are provided for feeding the supercooled liquid hydrogen into the second storage tank (2), which improve the mixing of the hydrogen fed into the storage tank (2) and the hydrogen present in the storage tank (2).

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