PRODUCTION OF HYDROGEN FROM SOLID BOROHYDRIDE
OR ALUMINOHYDRIDE ON BOARD A SUB-MARINE DEVICE
The present application relates to the field of propulsion of underwater 5 vehicles,
and, in particular, anaerobic propulsion (Air Independent Propulsion - AIP) with a fuel cell,
in particular with a hydrogen cell.
Anaerobic propulsion makes it possible to significantly increase the diving
autonomy of underwater vehicles, and to limit regular returns to the surface to run the
10 engines in order to recharge the batteries used in immersion, the latter representing
undesirable periods of indiscretion.
The ability to store as much hydrogen as possible in a limited volume is a
fundamental issue in AIP fuel cell power systems. Borohydrides or aluminohydrides (for
example KBH4, LiBH4, KAlH4, NaAlH4, LiAlH4 or NaBH4) are a means of storage and
15 production of hydrogen by hydrolysis. These borohydrides or aluminum hydrides are
denoted XH4 hereinafter.
The usual XH4 AIP systems are based on aqueous storage. Thus, WO
2017145068 proposes an AIP system with a Phosphoric Acid Fuel Cell (PAFC), and a
hydrogen production system based on NaBH4 solution in liquid form. NaBH4 is thus stored
20 in the form of an aqueous solution.
Storing XH4 solutions, however, presents significant technical disadvantages,
such as the weight, size and stability of the solutions.
It is therefore necessary to provide an alternative on-board storage means. The
present invention provides on-board storage of XH4 in solid form.
25 According to a first object, the present invention relates to a process for anaerobic
propulsion (AIP) of an underwater vehicle by production of hydrogen (H2) by hydrolysis of
XH4, where X is chosen from KB, LiB, KAl, NaAl, LiAl or NaB,
Characterized in that the on-board borohydride or aluminohydride reserve (XH4)
is stored in solid form.
30 Without being exhaustive, the present invention makes it possible to solve, inter
alia, the problems inherent in the aqueous storage of XH4:
• In the absence of water, the solid XH4 does not produce hydrogen, which makes
it possible to control the production of hydrogen during the underwater vehicle’s
mission;
35 • Suppression of unwanted hydrogen releases when hydrogen production is not
required;
2
• Elimination of XH4 crystallization problems that are not controlled in the
reservoirs;
• Increase in the quantity of on-board XH4 per unit of volume (the mass fraction of
hydrogen in solid XH4 being greater than a concentrated XH4 solution).
5
In particular, the process may be implemented according to one of the following
two alternative embodiments:
According to a first embodiment, said process comprises the injection of solid XH4
into the hydrolysis reactor.
According to this first embodiment, the solid XH4 is conveyed 10 to the reactor and
then injected into the reactor.
According to an alternative embodiment, said process comprises:
- the step of dissolving solid XH4 in an aqueous dissolution solution; and
- the step of injecting the XH4 aqueous solution thus obtained into the hydrolysis
15 reactor.
In this alternative embodiment, said process comprises:
- dissolution in the storage reservoir(s) of solid XH4, and/or
- conveying solid XH4 to a dissolution chamber and dissolving in said
dissolutionchamber, wherein the dissolution is effected by adding an aqueous
20 dissolution solution.
According to one or other of the alternative embodiments, the XH4 may, in
particular, be stored in the form of tablets ("caplets"), granules ("pellets") or powder.
The process according to the invention makes it possible, in particular, to create
25 an on-board XH4 aqueous solution whenever the hydrogen production reactor is supplied.
The fractionation of the dissolution makes it possible to dedicate a limited volume
to the dissolution of the XH4, and to decrease the concentration thereof so as to avoid any
risk of crystallization of the XH4 in solution, whatever the temperatures at which the
underwater vehicle is operating.
30
"On-board" means the storage of the XH4 on board an underwater vehicle,
generally involving a double limitation of a spatial order (reduced size) and energy (limited
consumption).
The terms “reserve” and “storage” are used here interchangeably to denote the
35 storage of XH4, in one or more containers.
3
The term “underwater vehicle”, in particular, means a submarine proper, or any
other equipment or underwater vehicle requiring a source of hydrogen supplied by XH4 for
its propulsion or its operation.
The term “hydrolysis reactor” denotes the apparatus generally consisting of at
least one container and a stirring means in which the reaction between 5 water and the XH4
is carried out, leading to the formation of hydrogen, depending on the reaction:
XH4 + 2 H2O -> 4 H2 + XO2
Where X is defined as above.
The term "aqueous dissolution solution" means a water-based solution used to
10 dissolve the solid XH4, so as to form an aqueous solution of XH4. Said aqueous dissolution
solution essentially contains water but may also contain one or more other dissolved agents,
such as aqueous NaOH or KOH bases which allow stabilization of the solution.
The term “dissolution chamber” denotes the apparatus generally consisting of at
least one container and a stirring means, in which the mixture of XH4 in water may be
15 produced, the mixture being able to be produced continuously.
According to one or other of the embodiments, the XH4 may be advantageously
stabilized by one or more bases.
Typically, the base(s) may be present in solid XH4, in the aqueous dissolution
solution, and/or in the aqueous solution of XH4.
20 According to one embodiment, said process comprises the initial priming step by
dissolving solid XBH4 with an aqueous priming solution.
According to one embodiment, said process further comprises recycling the
excess water to supply said aqueous dissolution solution.
By excess water is meant the water which has not reacted during hydrolysis, that
25 is available at the end of the H2 production phase, and which may be drawn off at the outlet
of the reactor.
According to another object, the present invention also relates to an anaerobic
propulsion system on board an underwater vehicle with production of hydrogen from solid
XH4 and comprising:
30 - a hydrolysis reactor 10 allowing the production of hydrogen 6 from XH4,
- at least one means 4 for introducing XH4 into said hydrogen production
system;
- at least one means 9 for transferring the hydrogen 6 so formed to a fuel cell;
characterized in that it comprises at least one storage reservoir 1 for solid XH4
35 2.
According to one embodiment, the system further comprises:
4
- at least one means of adding water 12 to the solid XH4 2,
- at least one dissolution chamber 11 allowing the dissolution of solid XH4 2 in
a dissolution solution 7;
- at least one means 4’, 4’’ for forced circulation of the XH4 solution between the
storage reservoir 1 of solid XH4 and the dissolution 5 chamber 11,
- at least one means 4 for transferring said XH4 solution thus formed to the
hydrolysis reactor 10.
The term "circulation" is understood here to mean circulation and recirculation
between the storage reservoir 1 of the solid XH4 and the dissolution chamber 11, and vice
10 versa.
According to one embodiment, the system further comprises:
- a reservoir of an aqueous priming solution 12’ upstream of a water inlet 12.
The two aforementioned embodiments may correspond to the process of the
invention according to the second embodiment.
15 According to one embodiment, the system comprises means 14 for recycling the
remaining water towards the water inlet.
The invention will be better understood upon reading the description which follows,
given solely by way of example and made with reference to the appended drawings, in
which:
20 Figure 1 shows schematically a system according to the invention, allowing the
implementation of the process according to the first embodiment.
Figure 2 shows schematically a system according to the invention, allowing the
implementation of the process according to the second embodiment.
Figure 1, in fact, illustrates a system for producing hydrogen from on-board solid
25 NaBH4 comprising: a reservoir denoted by the general reference 1 of solid XH4 denoted by
the general reference 2, said solid XH4 2 being conventionally transferred by a conveying
system provided with a valve denoted by the general reference 3, and a pump denoted by
the general reference 4, towards a hydrolysis reactor denoted by the general reference 10
allowing the production of hydrogen denoted by the general reference 6, from said solid
30 XH4 2.
The hydrogen 2 so formed is then extracted and transferred from the reactor to a
fuel cell, conventionally denoted by the general reference 9, for example by means of a
pump.
The system may include a pressure gauge represented by the general reference
35 5 connected to the pump 4, so as to measure the pressure of the hydrogen so formed, and
to modulate the input flow of the solid XH4.
5
The system of Figure 2 differs from that shown in Figure 1 in that it comprises
means for dissolving solid XH4 2, prior to introduction into the reactor 10. This configuration
allows the implementation of the second mode of carrying out the process according to the
invention.
This configuration comprises means for the arrival of an aqueous 5 solution denoted
by the general reference 12 at solid XH4 2, and means for the forced circulation of said
aqueous solution 7 between a dissolution chamber denoted by the general reference 11
and the storage reservoir 1 of the solid XH4 2, such as, for example, the pumps 4' and 4''.
Thus, water is added to the solid XH4 (2) and circulates between the reservoir 1
10 and the dissolution chamber 11, so as to form an aqueous solution of XH4 denoted by the
general reference 7.
At the outlet of the dissolution chamber 11, a pump 4 makes it possible to extract
the aqueous solution of XH4 7, and to transfer it to the hydrolysis reactor 10.
The aqueous solution 12, typically water, may come from a supply such as a
15 storage reservoir and/or may come from the recycling of the water obtained at the end of
the hydrolysis reaction.
Typically the system operates under a flow of nitrogen, denoted by the general
reference 13.

CLAIMS
1. Process of anaerobic propulsion (AIP) of an underwater vehicle by production
of hydrogen (H2) by hydrolysis of a borohydride or an aluminohydride 5 XH4, where X is
chosen from KB, LiB, KAl, NaAl, LiAl or NaB,
characterized in that the on-board XH4 reserve is stored in solid form.
2. Process according to claim 1 such that said process comprises the injection of
10 solid XH4 into the hydrolysis reactor.
3. Process according to claim 1 as it comprises:
- the step of dissolving solid XH4 in an aqueous dissolution solution; and
- the step of injecting the aqueous XH4 solution thus obtained, into the hydrolysis
15 reactor.
4. Process according to claim 3 comprising:
- dissolution in the storage reservoir(s) of solid XH4, and/or
- conveying solid XH4 to a dissolution chamber and dissolving it in said dissolution
20 chamber, the dissolution being effected by adding the aqueous dissolution
solution.
5. Process according to any one of the preceding claims, such that the XH4 is
stored in the form of tablets ("caplets"), granules ("pellets") or powder.
25
6. Process according to any one of the preceding claims such that the XH4 is
stabilized by one or more bases.
7. Process according to claim 6 such that the base(s) is/are present in solid XH4,
30 in the aqueous dissolution solution, and/or in the aqueous solution of XH4.
8. Process according to any one of claims 1, 3 to 6, comprising the initial priming
step by dissolving solid XH4 by an aqueous priming solution.
35 9. Process according to any one of claims 3 to 8 comprising the recycling of excess
water for the supply of said aqueous dissolution solution.
7
10. Anaerobic propulsion system on board an underwater vehicle based on
production of hydrogen from solid XH4 and comprising:
- a hydrolysis reactor (10) allowing the production of hydrogen (6) from XH4,
- at least one means (4) for introducing XH4 into said hydrogen production
5 system;
- at least one means (9) for transferring the hydrogen (6) so formed to a fuel cell;
characterized in that it comprises at least one storage reservoir (1) for solid XH4 (2).
11. System according to claim 10, further comprising:
10 - at least one means of adding water (12) to the solid XH4 (2),
- at least one dissolution chamber (11) allowing dissolution of the solid XH4 (2)
in a solution (7);
- at least one means (4’, 4’’) of forced circulation of the XH4 solution (2) between
the storage reservoir (1) of solid XH4 and the dissolution chamber (11),
15 - at least one means (4) for transferring said XH4 solution thus formed to the
hydrolysis reactor.
12. System according to claim 11, further comprising:
- a reservoir of an aqueous priming solution (12’) upstream of a water inlet (12).
20
13. System according to any one of claims 11 or 12 comprising means for
recycling (14) water in excess of the reaction, towards the water inlet (12).