Method for condensing a hydrogen stream

Abstract

The present invention provides a method for condensing a hydrogen gas stream (10), particularly a hydrogen BOG (boil-off gas) stream, comprising at least the steps of: (a) providing a hydrogen gas stream (10), particularly a hydrogen BOG stream; (b) providing a storage tank (2) containing liquid hydrogen and solid hydrogen (H2) in coexistence (3); (c) maintaining the coexistence of the liquid hydrogen and solid hydrogen in the storage tank (2) using a heat exchanger (4); (d) supplying the hydrogen gas stream (10) provided in step (a) to the storage tank (2); and (e) condensing the hydrogen gas (10) supplied to the storage tank (2) in step (d).

Description

[Technical Field]

[0001] The present invention relates to a method for condensing a hydrogen gas stream, particularly a hydrogen BOG (boil-off gas) stream. [Background technology]

[0002] Hydrogen is considered as one of the most promising energy carriers for decarbonized energy systems. Efficient transportation and storage of liquid hydrogen (LH2) are considered crucial for its large-scale deployment.

[0003] One of the main challenges in storing liquid hydrogen is dealing with boil-off losses due to the need for refrigeration, heat intrusion, the need to depressurize the storage tank, etc. Typically, boil-off gas flows are short in duration (on the order of a few hours), have relatively high flow rates (instantaneous flow rates of 3-4 times the average daily processing rate), and have low frequency (e.g., once a week or once a month).

[0004] The above-mentioned "intermittent" nature of such boil-off gas flow makes it difficult to deal with, for example, by mechanical equipment. Typically, intermittent hydrogen BOG is discharged. The paper "Final test results for the ground operations demonstration unit for liquid hydrogen" by Notardonato et al. in Cryogenics 88 (2017) 147-155 describes an LH2 system that uses IRAS (Integrated Refrigeration and Storage) technology aimed at ZBO (zero boil-off) operation, i.e., avoiding the generation of hydrogen BOG.

[0005] A problem with the above IRAS technology is that it is costly and complex. Another problem with IRAS technology is that while it reduces boil-off, for example during cargo transfer operations, it does not completely eliminate the occurrence of boil-off, and therefore boil-off treatment is still required. Furthermore, IRAS technology is not designed to reabsorb and reprocess intermittent boil-off gas flows. Summary of the Invention

[0006] It is an object of the present invention to solve, minimize or at least reduce one or more of the above problems associated with the treatment of boil-off gas losses. It is a further object of the present invention to provide an alternative method for condensing hydrogen gas streams, particularly hydrogen BOG streams.

[0007] One or more of the above objects or other objects may be achieved in accordance with the present invention by providing a method for condensing a hydrogen gas stream, in particular a hydrogen BOG (boil-off gas) stream, the method comprising at least (a) providing a hydrogen gas stream, particularly a hydrogen BOG stream; (b) providing a storage tank for containing liquid hydrogen and solid hydrogen (H2) in combination; (c) maintaining coexistence of liquid and solid hydrogen in the storage tank using a heat exchanger; (d) supplying the hydrogen gas stream provided in step (a) to a storage tank; (e) condensing the hydrogen gas supplied to the storage tank in step (d).

[0008] According to the present invention, it has surprisingly been found that by using the cooling capacity of solid hydrogen, the hydrogen gas (typically a hydrogen BOG stream) supplied to the storage tank in step (d) can be recondensed in a surprisingly simple manner, so that no discharge of the hydrogen BOG or its reprocessing outside the tank using a (very large) compression system is required.

[0009] A further advantage of the process according to the invention is that it allows for the re-liquefaction of (very) low pressure streams without the need for mechanical re-compression equipment. Furthermore, since the boil-off gas hydrogen is almost entirely in the parahydrogen spin state, no expensive catalytic spin-flip is required.

[0010] In step (a) of the method according to the invention, a flow of hydrogen gas is provided. Typically, the hydrogen gas stream provided in step (a) is a hydrogen BOG stream derived from liquid hydrogen handling and storage operations and therefore has a high hydrogen content and low impurities (which would otherwise freeze in the conduits to the storage tanks). The hydrogen BOG gas stream can originate from a variety of sources (combinations), such as hydrogen BOG generated during hydrogen cooling, heat intrusion into some parts of the hydrogen supply chain, depressurization of storage tanks, etc.

[0011] Preferably, the hydrogen gas stream provided in step (a) comprises at least 99.0% by weight, preferably at least 99.999% by weight, more preferably at least 99.99999% by weight hydrogen.

[0012] Furthermore, it is preferred that the hydrogen gas stream provided in step (a) comprises at least 90% by weight, preferably at least 95% by weight, parahydrogen. The temperature of the hydrogen gas stream provided in step (a) is not particularly limited, but preferably the hydrogen gas stream provided in step (a) has a temperature in the range of 14 to 60K, preferably less than 40K.

[0013] Furthermore, the pressure of the hydrogen gas stream provided in step (a) is not particularly limited, but preferably the hydrogen gas stream provided in step (a) has a pressure in the range of 0.1 to 5.0 bara, preferably up to 2.0 bara.

[0014] In step (b) of the method according to the invention, a storage tank is provided containing liquid hydrogen and solid hydrogen (H2) in combination. Those skilled in the art will readily understand how to provide a storage tank that contains both liquid and solid hydrogen (H), and this will not be discussed in further detail here. Generally, such a storage tank is obtained by partially filling the storage tank with liquid hydrogen. The storage tank is then cooled (which may take days or weeks) to a point where a significant amount of the liquid hydrogen is converted to solid hydrogen (thereby extracting phase change energy from the system). As a result, a certain amount of solid or slush hydrogen is formed within the storage tank.

[0015] Preferably, the storage tank operates at a pressure in the range of 0.05 to 5.0 bara, preferably up to 2.0 bara. Preferably, the storage tank in step (b) contains a solid hydrogen fraction of at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight, based on the total amount of liquid and solid hydrogen in the storage tank.

[0016] It is particularly preferred that in step (b) the storage tank contains solid hydrogen in an amount at least twice, preferably at least four times, more preferably at least eight times the amount of hydrogen gas stream fed to the storage tank in step (d).

[0017] It is also preferred that the storage tank provided in step (b) has a cooling capacity at least 1 time, preferably at least 1.5 times, more preferably at least 2 times the capacity required to condense the hydrogen gas provided in step (d).

[0018] In step (c) of the method according to the invention, the coexistence of liquid and solid hydrogen in the storage tank is maintained using a heat exchanger. Typically, this is done using an internal heat exchanger which may be (and usually is) connected to an external (helium) cooling cycle including a cryocooler.

[0019] In step (d) of the method according to the invention, the hydrogen gas stream provided in step (a) is fed to a storage tank. Preferably, the hydrogen gas stream supplied to the storage tank in step (d) has a flow rate equivalent to at least 10% by weight, preferably at least 25% by weight, of the solid hydrogen present in the storage tank per hour.

[0020] Additionally, the hydrogen gas is preferably supplied via the bottom side of the storage tank below the fluid level of the solid and liquid hydrogen within the storage tank, allowing for intimate contact with the solid hydrogen.

[0021] In step (e) of the method according to the invention, the hydrogen gas provided to the storage tank in step (d) is condensed by using the available cooling capacity of the solid hydrogen. In another aspect, the present invention provides an apparatus suitable for carrying out the method for condensing hydrogen according to the invention, the apparatus comprising at least - a storage tank that accommodates liquid hydrogen and solid hydrogen (H2) in a coexistent state; a heat exchanger disposed within the storage tank; The storage tank has an inlet for the flow of hydrogen gas.

[0022] Preferably, the heat exchanger is connected to an external cryocooler as part of a refrigeration cycle. Furthermore, the inlet is preferably connected to a gas distributor located inside the storage tank, preferably capable of distributing gas below the fluid level of the liquid and solid hydrogen in the storage tank.

[0023] The invention will now be further illustrated by the following non-limiting figures, in which: [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic flow diagram of a method for condensing hydrogen according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0025] For purposes of this description, the same reference numbers refer to the same or similar components. The flow diagram of FIG. 1 is generally referenced by the reference numeral 1 and shows an external (helium) cooling cycle containing a hydrogen storage tank 2 containing liquid and solid hydrogen coexisting (in the form of hydrogen slush 3), an internal heat exchanger 4, and a cryocooler 5.

[0026] In use, a hydrogen gas stream (preferably a hydrogen BOG stream) 10 is provided and fed via inlet 21 to storage tank 2, which contains slush hydrogen 3. Typically, hydrogen gas stream 10 is fed intermittently, i.e., the boil-off gas flow is short in duration (on the order of a few hours), has a relatively high flow rate (an instantaneous flow rate of 3-4 times the average daily treatment rate) and a low frequency (e.g., once a week or once a month).

[0027] The coexistence of liquid and solid hydrogen in the storage tank 2 is maintained using a heat exchanger 4 connected to an external cryocooler 5 . 1, hydrogen gas stream 10 is supplied to storage tank 2 via inlet 21 located at the bottom of storage tank 2. Gas distributor 6 distributes the gaseous hydrogen below the fluid level of slush hydrogen 3 within storage tank 2, ensuring intimate contact of the hydrogen gas with slush hydrogen 3. As a result, the hydrogen gas supplied to storage tank 2 is condensed by using the available cooling capacity of the solid hydrogen.

[0028] Also shown in FIG. 1 is an outlet 22 for liquid hydrogen (LH2) 20, which can be used to remove the LH2 20 if desired. Consideration As can be seen from FIG. 1, the method according to the present invention allows for a surprisingly simple and effective way of condensing a hydrogen stream, particularly a hydrogen BOG stream.

[0029] An important advantage of the present invention is that it does not require the discharge of hydrogen BOG or its reprocessing outside the tank using a (very large) compression system. Those skilled in the art will readily appreciate that many modifications may be made without departing from the scope of the present invention. Furthermore, those skilled in the art will readily appreciate that, although the present invention has been described in some instances with reference to particular combinations of features and means, many of these features and means are functionally independent of other features and means provided in each embodiment and may be equally or similarly applied independently in other embodiments.

Claims

1. A method for condensing a hydrogen gas stream (10), in particular a hydrogen BOG (boil-off gas) stream, comprising at least (a) providing a hydrogen gas stream (10), in particular a hydrogen BOG stream; (b) Liquid hydrogen and solid hydrogen (H ２ providing a storage tank (2) for containing the coexistence (3) of (c) maintaining the coexistence of liquid and solid hydrogen in said storage tank (2) using a heat exchanger (4); (d) feeding the hydrogen gas stream (10) provided in step (a) into the storage tank (2); (e) condensing the hydrogen gas (10) provided to the storage tank (2) in step (d).

2. 2. The method of claim 1, wherein the hydrogen gas stream (10) provided in step (a) comprises at least 99.0 wt.%, preferably at least 99.999 wt.%, more preferably at least 99.99999 wt.% hydrogen.

3. 3. The method of claim 1 or 2, wherein the hydrogen gas stream (10) provided in step (a) comprises at least 90 wt.%, preferably at least 95 wt.% parahydrogen.

4. The method according to any one of claims 1 to 3, wherein the hydrogen gas stream (10) provided in step (a) has a temperature in the range of 14 to 60K, preferably below 40K.

5. The method according to any one of claims 1 to 4, wherein the hydrogen gas stream (10) provided in step (a) has a pressure in the range of 0.1 to 5.0 bara, preferably up to 2.0 bara.

6. The method according to any one of claims 1 to 5, wherein the storage tank (2) is operated at a pressure in the range of 0.05 to 5.0 bara, preferably up to 2.0 bara.

7. 7. The method according to any one of claims 1 to 6, wherein in step (b) the storage tank (2) contains solid hydrogen in an amount at least twice, preferably at least four times, more preferably at least eight times the amount of the hydrogen gas stream (10) supplied to the storage tank (2) in step (d).

8. 8. The method according to any one of claims 1 to 7, wherein the storage tank (2) provided in step (b) has a cooling capacity at least 1 time, preferably at least 1.5 times, more preferably at least 2 times the capacity required to condense the hydrogen gas provided in step (d).

9. 9. The method according to any one of claims 1 to 8, wherein the hydrogen gas stream (10) supplied to the storage tank (2) in step (d) has a flow rate corresponding to at least 10% by weight, preferably at least 25% by weight, of the solid hydrogen present in the storage tank per hour.

10. An apparatus (1) suitable for carrying out the method for condensing hydrogen according to any one of claims 1 to 9, comprising at least Liquid hydrogen and solid hydrogen (H ２ a storage tank (2) for storing the above-mentioned components in a coexistent state (3); a heat exchanger (4) disposed in the storage tank (2); The storage tank (2) has an inlet (21) for the hydrogen gas stream (10) to be recondensed.

11. 11. The apparatus (1) according to claim 10, wherein the heat exchanger (4) is connected to an external cryocooler (5).

12. 12. The device (1) according to claim 10 or 11, wherein the inlet (21) is connected to a gas distributor (6) arranged inside the storage tank (2).

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