U.S. patent application number 09/894010 was filed with the patent office on 2003-03-06 for method for storing hydrogen in an hybrid form.
Invention is credited to Huot, Jacques, Larochelle, Patrick, Liang, Guoxian, Schulz, Robert.
Application Number | 20030042008 09/894010 |
Document ID | / |
Family ID | 25402479 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030042008 |
Kind Code |
A1 |
Schulz, Robert ; et
al. |
March 6, 2003 |
Method for storing hydrogen in an hybrid form
Abstract
A method for storing hydrogen which combines the advantages of
at least two known methods for storing hydrogen, selected amongst
the methods for storing hydrogen in a gaseous form, in a liquid
form and in a solid form. More specifically, the above method
consists in coupling and using in a single tank at least two of the
methods for storing hydrogen mentioned hereinabove, namely: A) the
method for storing hydrogen in a gaseous form; B) the method for
storing hydrogen in a liquid form; and C) the method for storing
hydrogen in a solid form, in volume or surface, preferably by means
of a suitable hydride. The only condition is that each of the above
methods be used for storing at least 5% by weight of the total
amount of hydrogen to be stored within a tank. Such a method
permits to obtain fast release of hydrogen whenever required while
ensuring high storage capacities. It also permits to satisfy
transitory periods especially during the accelerations of a
hydrogen-powered automotive vehicle.
Inventors: |
Schulz, Robert; (Ste-Julie,
CA) ; Liang, Guoxian; (Longueuil, CA) ; Huot,
Jacques; (Boucherville, CA) ; Larochelle,
Patrick; (St-Amable, CA) |
Correspondence
Address: |
Glenn Law
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
25402479 |
Appl. No.: |
09/894010 |
Filed: |
June 29, 2001 |
Current U.S.
Class: |
165/104.12 |
Current CPC
Class: |
Y02E 60/32 20130101;
F17C 11/005 20130101; F17C 13/002 20130101; C01B 3/0031
20130101 |
Class at
Publication: |
165/104.12 |
International
Class: |
F28D 015/00 |
Claims
1. A method for storing hydrogen in a hybrid form, comprising
coupling and using within a single tank at least two hydrogen
storage means selected from the group consisting of: a) means for
storing hydrogen in a gaseous form b) means for storing hydrogen in
a liquid form; and c) means for storing hydrogen in a solid form by
absorption or adsorption, with the proviso that each of the means
for storing hydrogen that are used, is sized to store at least 5%
by weight of the total amount of hydrogen stored within the
tank.
2. The method according to claim 1, wherein the means that are
coupled and used, include said means for storing hydrogen in a
gaseous form and said means for storing hydrogen in solid form with
a metal hydride.
3. The method according to claim 2, wherein the metal hydride has
an equilibrium plateau pressure higher than 40 bar at the operating
temperature of the tank.
4. The method according to claim 3, wherein the hydride is a Ti- or
alanate (AlH.sub.x) based hydride.
5. The method according to claim 1, wherein the means that are
coupled and used, include said means for storing hydrogen in a
liquid form and said means for storing hydrogen in a solid form
with a metal hydride.
6. A hybrid tank for storing hydrogen in both liquid and solid
forms, comprising two concentric containers, one of said containers
hereinafter called "inner container" being located within the other
one which is hereinafter called "outer container", said containers
being separated by an insulating sleeve for maintaining the inner
container at low temperature, said inner container being used for
storing hydrogen in a liquid form, said outer container being in
direct communication with the inner container and containing a
metal hydride for storing hydrogen in a solid form.
7. The hybrid tank according to claim 6, wherein the hydride that
is used in the outer container is an hydride having low equilibrium
plateau pressure at the operating temperature of the tank.
8. The hybrid tank according to claim 7, wherein the hydride that
is used is selected from the group consisting of NaAlH.sub.4,
LiAlH.sub.4, LaNi.sub.5H.sub.6 and MgH.sub.2.
9. The hybrid tank according to claim 6, wherein the hydride within
the outer container is an hydride having a high equilibrium plateau
pressure at the operating temperature of the tank.
10. The hybrid tank according to claim 9, wherein the hydride is
selected from the group consisting of TiCr.sub.1.8, TiMn.sub.2-y,
Hf.sub.2Cu, Zr.sub.2Pd, TiCu.sub.3 and V.sub.0.855
Cr.sub.0.145.
11. A hybrid tank for storing hydrogen in both solid and gaseous
forms, comprising: a container having a metallic liner or inner
wall covered with a polymeric outer shell, said container being
devised to store hydrogen in gaseous form at a high pressure and to
receive and store a metal hydride in order to also store hydrogen
in solid form; at least one heat pipe mounted in the container to
allow circulation of a heat carrying fluid within said container;
and a heat exchanger located within the container in order to
ensure thermal connection between said at least one heat pipe and
the hydride.
12.The hybrid tank according to claim 11, wherein: the container is
cylindrical and provided with an axial opening; the tank comprises
only one of said at least one heat pipe which is inserted into the
container through the opening thereof and extends axially within
said container; and the heat exchanger consists of at least one
element selected from the group consisting of metallic grid, fibers
or porous metallic structure extending transversally within the
container, each of said at least one grid being in direct contact
with the axial heat pipe, the metallic liner of the container and
the hydride.
13. The hybrid tank according to claim 12, wherein the hydride that
is used in the outer container is an hydride having low equilibrium
plateau pressure at the operating temperature of the tank.
14. The hybrid tank according to claim 13, wherein the hydroxide
that is used is selected from the group consisting of NaAlH.sub.4,
LiAlH.sub.4, LaNi.sub.5H.sub.6 and MgH.sub.2.
15. The hybrid tank according to claim 12, wherein the hydride
within the outer container is an hydride having a high equilibrium
state at the operating temperature of the tank.
16. The hybrid tank according to claim 15, wherein the hydride is
selected from the group consisting of TiCr.sub.1.8 TiMn.sub.2-y,
Hf.sub.2Cu, Zr.sub.2Pd, TiCu.sub.3 and V.sub.0.855 Cr.sub.0.145.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for storing
hydrogen in a hybrid form. More specifically, it relates to a
method for storing hydrogen in two different forms within a single
tank.
[0002] The invention also relates to tanks hereinafter called
"hybrid tanks", which are specially adapted for carrying out the
above method when the hydrogen is stored in liquid and solid forms
and when the hydrogen is stored in solid and gaseous forms,
respectively.
BRIEF DESCRIPTION OF THE PRIOR ART
[0003] Methods for storing hydrogen can be classified in three main
categories:
[0004] (A) gaseous storage in high pressure tanks;
[0005] (B) liquid storage in cryogenic tanks; and
[0006] (C) solid storage in tanks containing materials that absorb
(in volume) or adsorb (on surface) hydrogen.
[0007] The last category listed above as category (C) is the one
that makes use of metal hydride storage tanks.
[0008] Each of the above categories has advantages and
disadvantages that are summarized in the following Table I:
1TABLE I Characteristics of the different methods for storing
hydrogen Storing method Advantages Disadvantages (A) Gaseous The
filling and discharge kine- Very low storage capacity per volume
unit and, tics (sec-min) is very fast accordingly, the necessity of
using very large tanks The tanks made of composite Very high gas
pressure is required to have a sufficient material are of very
tight weight amount of hydrogen per volume unit (up to 10000 psi
690 bars) Significant loss of energy because mechanical compression
is required to achieve the requested pressure level (15-20%). Risk
of explosion or deflagration due to the very high pressure (B)
Liquid Excellent storage capacity per Problem of evaporation of
liquid hydrogen (boil off) volume unit Significant loss of energy
because refrigeration is required to reach the requested
temperatures (30%) (C) Solid (hydrides) Excellent storage capacity
per Very low filling and discharge kinetics since the absorption
and "Hydrogen absorption in volume unit which sometimes desorption
of hydrogen is limited by the heat transfer (min-hr). volume"
exceeds the one of liquid storage Low storage capacity per weight
unit because of the high weight of the absorbent material
Significant loss of thermal energy for inducing hydrogen Solid
(adsorbents) High storage capacity for some desorption (10-25%)
"Hydrogen adsorption on materials of high specific surface
Necessity of using very low temperatures (liquid nitrogen) to
surface" (activated carbon, etc. . . ) obtain a high storing
capacity
[0009] By way of example, in the case of a method for storing
hydrogen in a gaseous form (category A), a tank of one (1) liter
will contain the following amounts of hydrogen at the various
pressures indicated in Table II:
2TABLE II Gaseous storage Hydrogen pressure Amount of hydrogen
within one liter 3,600 psig (248 bar) 0.0177 kg 5,000 psig (345
bar) 0.0233 kg 8,000 psig (550 bar) 0.0334 kg 10,000 psig (690 bar)
0.0392 kg 15,000 psig (1,035 bar) 0.0512 kg
[0010] In the case of a method for storing hydrogen in a liquid
form (category B), a tank of one (1) liter will contain 0.0708 kg
of hydrogen since the density of liquid hydrogen at -252.8.degree.
C. (that is at the conventional boiling point of hydrogen) is equal
to 0.0708 kg/l.
[0011] Last of all, in the case of a method for storing hydrogen in
a solid form with a metal hydride (category C), a tank of one (1)
liter containing a hydride of formula AB.sub.5 like
LaNi.sub.5H.sub.6 (density: 6.59 kg/l, hydrogen storage capacity
.congruent.1.4%) occupying all the volume of the tank, will contain
0.0923 kg of hydrogen, that is almost twice the amount of hydrogen
stored in a gaseous form in a tank of one liter at 15,000 psig.
[0012] The results of this comparative example are given in Table
III:
3TABLE III Comparison of the storage capacity of the thru basic
methods for storing hydrogen Amount of hydrogen stored within
Method a tank of one liter (A) Gaseous storage at 15,000 psig
0.0512 kg (1,035 bar) at ambient temperature (B) Liquid storage at
-252.8 C. 0.0708 kg (1 bar) (C) Solid storage in a hydride of
0.0923 kg LaNi.sub.5 (10 bar) at ambient temperature
[0013] Of course, in the case of the method for storing hydrogen in
a liquid form (category B), there is always some gaseous hydrogen
in equilibrium with the liquid because of some evaporation of the
latter. Also, in the case of the method for storing hydrogen in a
solid form with a metal hydride (category C) typically operating at
low pressure (10 bar), there is some gaseous hydrogen because the
hydride never occupies all the space in the tank. Moreover, in the
case of the method for storing hydrogen in a gaseous form at a very
high pressure (category A), there is always some hydrogen that is
adsorbed (such adsorbed hydrogen is also called "solid hydrogen"
according to the above terminology) onto the internal walls of the
tank. Therefore, in each method listed hereinabove (gaseous, liquid
and solid), there is always a small amount of hydrogen that is
stored according to another method of storage.
[0014] By way of example, one may evaluate the maximum percentage
of hydrogen that may come from another method of storage in the
case of a tank of one liter containing a metal hydride powder
(LaNi.sub.5H.sub.6). Assuming that the powder is not compacted and,
therefore, occupies about half of the volume of the tank, that is
about half a liter, considering also that the density of
LaNi.sub.5H.sub.6 is equal to 6.59 kg/l and further assuming that
the gaseous hydrogen within the tank (about half a liter) is at a
pressure 10 bar, the amount of hydrogen that is not solid within
the tank of one liter will be as reported in Table IV:
4TABLE IV "Gaseous" hydrogen (10 bar) "Solid" hydrogen Total amount
of hydrogen 0.00041 kg (0.9%) 0.0462 kg (99.1%) 0.0466 kg
(100%)
[0015] This example clearly shows that for any given method of
storage, there can usually be 1% of hydrogen stored in a different
form. However, in all cases, this amount will always be lower than
5% by weight.
[0016] It has already been suggested that there could be some
advantages in coupling different means for storing hydrogen within
a single category.
[0017] By way of example, U.S. Pat. No. 5,906,792 entitled
"Nanocrystalline composite for hydrogen storage" in the name of the
Applicant and the McGill University, discloses that there are
advantages when one combines within a same tank a low temperature
metal hydride with a high temperature metal hydride in contact with
each other. When such a mixture is used for an internal combustion
engine, the low temperature metal hydride allows cold starting of
the engine by providing the hydrogen at the start up. When the
engine is hot, the heat that is generated by the same permits to
induce the desorption of hydrogen from the high temperature metal
hydride (see column 3 of this U.S. Pat. No. 5,906,792 for more
details).
[0018] Similarly, international laid-open patent application No. WO
01/16021 published on Mar. 8, 2001 in the name of David G. SNOW et
al, discloses that there are some advantages in combining solid
storage in the volume (absorption) with solid storage on the
surface (adsorption) in nanoparticles of a hydride in order to
improve, inter alia, the hydrogen absorption and desorption
kinetics.
[0019] U.S. Pat. No. 5,872,074 entitled ((Leached nanocrystalline
materials, process for manufacture the same and use thereof in the
energetic field" in the name of the Applicant, also discloses that
the hydrogen sorption kinetics can be improved when use is made of
a hydride having high specific surface.
[0020] Independently of the above, it is also known that the method
(C) for storing hydrogen in a solid form usually has a response
time (loading and unloading) much slower than the method (A) for
storing hydrogen in a gaseous form and slower than the method (B)
for storing hydrogen in a liquid form.
[0021] Actually, at least 15 minutes and sometimes more than 1 hour
are required to fill up a hydride storage tank. In spite of this
drawback, the method for storing hydrogen in a solid form has the
highest capacity of storage per volume unit (see again Table III
hereinabove).
[0022] It is known that some technical applications require a
response time much faster than one minute.
[0023] Thus, for example, in UPS systems (uninterruptible power
supply) using fuel cells fed with hydrogen, a response time of
about one hundred milliseconds is usually required. Of course, a
hydrogen storing tank using metal hydride cannot satisfy this
particular requirement. However, in such a case, use could be made
of a tank in which hydrogen is stored in a gaseous form at high
pressure.
[0024] Similarly, in hydrogen operated vehicles, there are
different types of transitory periods, like:
[0025] short duration accelerations (second) which usually require
a response time of about one hundred millisecond from the
propulsion system; and
[0026] power increases when the vehicle is climbing up a hill,
which may last a few minutes.
[0027] In hybrid vehicles which make use of a fuel cell and
batteries, the very short accelerations (second) can be taken care
by the batteries whereas the transitory periods of a longer
duration (a few minutes) may require hydrogen stored in a gaseous
form. On the other hand, the average power which is of about 20 KW
for a typical vehicle, may easily be accomodated by a metal hydride
tank. The energy contained in the batteries of such a vehicle
usually represents about 1% of the energy on board. Therefore, one
needs an amount of hydrogen higher than 1% to take charge of the
transitory periods.
[0028] To sump up, in view of the above, it is obvious that there
is presently a major need for a method for storing hydrogen which
would combine the advantages of the different methods listed
hereinabove.
OBJECT AND SUMMARY OF THE INVENTION
[0029] An object of the present invention is to satisfy the above
mentioned need by providing a new method for storing hydrogen which
combines the advantages of at least two of the above mentioned
methods for storing hydrogen, namely the methods for storing
hydrogen in a gaseous form, in a liquid form and in a solid
form.
[0030] The present invention basically consists in coupling and
using in a single tank hereinafter called <<hybrid tank for
storing hydrogen>> at least two of the methods for storing
hydrogen mentioned hereinabove, namely:
[0031] A) the method for storing hydrogen in a gaseous form
[0032] B) the method for storing hydrogen in a liquid form; and
[0033] C) the method for storing hydrogen in a solid form, in
volume or on surface.
[0034] The only condition is that each of the above methods is used
for storing at least 5% by weight of the total amount of hydrogen
within the tank.
[0035] Therefore, the invention as claimed is directed to a method
for storing hydrogen in an hybrid form, which comprises the step of
coupling and using within a single tank at least two hydrogen
storage means selected from the group consisting of:
[0036] a) means for storing hydrogen in a gaseous form
[0037] b) means for storing hydrogen in a liquid form; and
[0038] c) means for storing hydrogen in a solid form by absorption
or adsorption,
[0039] with the proviso that each of the storing means that are
used, is sized to store at least 5% by weight of the total amount
of hydrogen stored within the tank.
[0040] The means mentioned hereinabove for storing hydrogen in
different forms are those commonly used for carrying out each of
the above mentioned methods. They are very conventional and need
not be further described in detail. The only requirement is that
they be coupled within the same tank in order to be used
simultaneously for each storing at least 5% by weight of the
hydrogen.
[0041] Another object of the present invention is to provide a
hybrid tank for storing hydrogen in both liquid and solid forms,
comprising two concentric containers, one of the containers
hereinafter called "inner" container is located within the other
one which is hereinafter called "outer container", the containers
being separated by an insulating sleeve for maintaining the inner
container at low temperature. The inner container is used for
storing hydrogen in a liquid form. The outer container is in direct
communication with the inner container and contains a metal hydride
for storing hydrogen in a solid form.
[0042] A further object of the present invention is to provide a
hybrid tank for storing hydrogen in both solid and gaseous forms,
comprising:
[0043] a container having a metallic liner or inner wall covered
with a polymeric outer shell, said container being devised to store
hydrogen in gaseous form at a higher pressure and to receive and
store a metal hydride in order to store hydrogen in solid form;
[0044] at least one heat pipe mounted within the container to allow
circulation of a heat carrying fluid; and
[0045] a heat exchanger located within the container in order to
ensure thermal connection between said at least one heat pipe and
the hydride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The invention and the way it can be reduced to practice will
be better understood upon reading the following non-limitative
examples given with reference to the accompanying drawings in
which:
[0047] FIG. 1 is a diagram illustrating the equilibrium plateau of
the hydride used in a hybrid gas-solid storage tank disclosed in
example 1;
[0048] FIG. 2 is a schematic cross-sectional view of the hybrid
liquid-solid storage tank disclosed in example 2;
[0049] FIG. 3 is a diagram illustrating the equilibrium plateau of
the hydride used in the hybrid gas-solid storage tank disclosed in
example 3;
[0050] FIG. 4 is a schematic cross-sectional view of the hybrid
gas-solid storage tank disclosed in example 3; and
[0051] FIGS. 5 and 6 are diagrams giving the equilibrium plateaux
of several hydrides as a function of the temperature and indicating
which one could be used in the hybrid gas-solid storage tank
disclosed in examples 1 and 3.
EXAMPLE 1
Hybrid storage Tank for Storing Hydrogen in Gas and Solid Forms
[0052] A hydrogen storage tank having a volume of 1 liter has been
filled up with a powder of nanoparticles of a hydride of LaNi.sub.5
having an average diameter of 5 nanometers. The powder occupied 50%
by volume of the tank, that is 0.5 liter, since it was not
compacted. The number of atoms on the surface of these
nanoparticles represented about 28% of the total amount of atoms
within each particle considering a layer of 0.4 to 0.5 nanometer on
the surface of each nanoparticle. The tank has then been filled up
with gaseous hydrogen at different pressures ranging from 10 bar
(typical pressure of use of the metal hydride tanks) to 700 bars
(typical pressure used in high pressure gaseous tanks). It was
assumed that the amount of hydrogen in the volume and at the
surface of the metal hydride corresponded to H/M=1 (H=hydrogen,
M=metal), which is typical to most metal hydrides. Under these
conditions, the amounts of hydrogen associated to the two different
means of storage that were used, have been calculated and are
reported in Table V hereinafter:
5TABLE V Hydrogen Hydrogen bound pressure Hydrogen in connected to
the Hydrogen within gaseous phase surface of the inserted within
Total amount of the tank (kg) % hydride % the hydride % hydrogen
(kg) 10 bar * 0.0004 1 0.0142 28 0.0365 71 0.0511 150 psi 248 bar
0.0089 15 0.0142 24 0.0365 61 0.0596 3600 psi 345 bar 0.0117 19
0.0142 23 0.0365 58 0.0624 5000 psi 690 bar 0.0196 28 0.0142 20
0.0365 52 0.0703 10000 psi
[0053] It is worth noting that in the first case reported in Table
V, that is when the pressure is of 150 psi (10 bar), the amount of
hydrogen in gaseous phase represented about 1% of the total amount.
This example is illustrative of what is presently obtained in
conventional metal hydride tanks and is therefore outside the scope
of the present invention. However, in the three other cases
reported hereinabove where the pressures were of 3,600 psi, 5,000
psi and 10,000 psi, the amounts of hydrogen in gaseous phase
represented about 15%, 19% and 28% respectively of the total amount
of hydrogen within the tank. Such is much higher than the limit of
5% as indicated hereinabove.
[0054] The tank disclosed in example 1 is illustrative of a tank
that can be used in a "back up" system based on a fuel cell or a
hydrogen source generator. In the case of a failure of the electric
supply, the hydrogen in the gaseous phase will initially supply the
fuel cell or the generator that will slowly warm up. The pressure
within the tank will be reduced. When the pressure reaches the
equilibrium plateau of the hydride, that is about 2 bars for a
AB.sub.5 alloy at room temperature, there will be almost no more
hydrogen in the gaseous phase. Then, the hydride will take over by
providing hydrogen to the system thanks to the heat generated by
the fuel cell or the generator.
[0055] It is worth noting that, in this example, the equilibrium
plateau of LaNi.sub.5 which is a conventional low temperature metal
hydride at the operating temperature (typically ranging between 0
to 100.degree. C.), is slightly higher than the pressure of
hydrogen required at the inlet of the fuel cell, which typically
about 2 bars. If the tank contains 50% by volume of hydride and the
balance is occupied with gaseous hydrogen at 690 bars (10,000 psi),
the situation will correspond to that of the diagram given in FIG.
1.
[0056] Under such a circumstance, during operation of the system,
the hydrogen will come first from the gaseous phase. Then, when the
amount of hydrogen and the gas pressure become low, the hydride
will take over by providing hydrogen to the system. The pressure
within the tank will then be kept at the level of the desorption
plateau of the hydride. The kinetics of the system will therefore
be quite high at the beginning (response time of the gaseous
system) and thereafter low (response time of the hydride
system).
[0057] There are also other advantages in using such a hybrid
method combining gas and solid storage. In particular, one can
mention:
[0058] a) refilling up of the tank is carried out in a short time
as compared to conventional metal hydride tanks;
[0059] b) the design of the heat transfer components of the tank is
simplified; and
[0060] c) the high storage capacity by volume of the metal hydride
and the high capacity of storage by weight of the new composite
high pressure gas storage tanks are combined.
EXAMPLE 2
Hybrid Tank for Storing Hydrogen in Liquid and Solid Forms
[0061] A hybrid tank 1 for storing hydrogen having a total volume
of one liter has been devised from two concentric containers 3,5
(see FIG. 2). The inner container 3 had a volume of 0.8 liter
whereas the outer container 5 had a volume of 0.2 liter. An
insulating sleeve 7 was positioned between the inner and the outer
containers 3,5 to keep the inner container 3 at low
temperature.
[0062] In use, the inner container 3 of the tank 1 was filled up
with liquid hydrogen. It contained about 0.0708 kg/l.times.0.8
liter =0.0566 kg of hydrogen. The outer container 5 was filled with
a powder of a metal hydride of the type LaNi.sub.5H.sub.6 which
occupied about 50% of the volume, that is about 0.1 liter.
Therefore, the outer container 5 contained 6.59 kg/l .times.0.1
liter.times.1.4% =0.0092 kg of hydrogen. The total amount of
hydrogen stored within the tank 1 was equal to 0.0658 kg (14% in
the outer tank and 86% in the inner tank).
[0063] As compared to a conventional tank for storing hydrogen in a
liquid form, the tank disclosed in example 2 has the advantage of
having no loss of hydrogen over a period that may exceed two weeks.
Indeed, the problem with any conventional liquid hydrogen storage
tank is that the hydrogen evaporates (boil off). Up to 1% of the
amount of liquid hydrogen can evaporate each day from a
conventional tank (1% x 0.0566 kg=0.0006 kg/day). In the hybrid
tank disclosed in example 2, the boil-off hydrogen is absorbed by
the metal hydride that extends in periphery of the inner container
and up to its maximum capacity (that is 0.0092 kg/0.0006 kg/day =15
days).
[0064] It is worth noting that the idea of using metal hydrides for
"catching" evaporated hydrogen from a liquid hydrogen storage tank
has already been suggested, but by means of two separate systems
that must be interrelated, connected and independently controlled.
In this regard, one can refer to U.S. Pat. No. 5,728,483 to SANYO
ELECTRIC CO. In contrast, in the present invention, these two
different means for storing hydrogen are combined within a single
tank and therefore operate in a simpler manner.
EXAMPLE 3
Hybrid Tank for Storing Hydrogen in Gas-Solid Form for use in a
System Having Transitory Periods
[0065] In the tank disclosed in example 1, use was made of
LaNi.sub.5H.sub.6 as the hydride. This compound is known to have a
low equilibrium plateau (viz. lower than 40 bar) at operating
temperature. Use could also have been made of other hydride with a
low equilibrium plateau, such as NaAlH.sub.4, LiAlH.sub.4 or
MgH.sub.2.
[0066] According to the invention, it is however possible to use
also a hydride having an equilibrium plateau that is much higher at
the operating temperature (typically ranging between 0.degree. and
100.degree. C.) than the equilibrium plateau of the conventional
hydrides (typically ranging between 1 to 10 bar). Such a high
equilibrium plateau is 40 bar or higher . An example of such
hydrides is TiCr.sub.1.8 which has an equilibrium plateau at room
temperature much higher than 100 bars (see FIG. 6). There are also
medium temperature hydrides with equilibrium plateau at high
pressures, like TiMn.sub.2-y, Hf.sub.2Cu, Zr.sub.2Pd, TiCu.sub.3 or
V.sub.0.855 Cr.sub.0.145 which can be of interest for this kind of
application (see FIGS. 5 and 6).
[0067] Under these circumstances, when there is a need for
hydrogen, the gaseous system of the storage tank will permit to
accommodate such a request with a very short response time (t1) of
about one second (for example in the case of a car that
accelerates). When the pressure within the tank drops and changes
from a value (1) to a value (2) (see FIG. 3), the hydride will
regenerate the gaseous system with a lower response time (t2) of a
few minutes, until the next acceleration.
[0068] This hybrid method makes it possible to substantially
simplify the structural components required for heat transfer in
order to induce the desorption from the hydride or absorption
therein. Moreover, this hybrid method permits, thanks to the high
pressure, to solve the problem of refilling hydrides such as the
alanates (NaAlH.sub.4 or LiAlH.sub.4). As to the kind of hydrides
that can be used, reference can be made to FIG. 5 (hydrides of the
AB.sub.5 type) and FIG. 6 (hydrides of the AB.sub.2 type) enclosed
herewith.
[0069] As an example of the way this method could be carried out,
reference can be made to FIG. 4 which shows a hybrid tank 11 for
storing hydrogen in both solid and gaseous form. The tank 11
comprises a container having a metallic liner or inner wall 15
covered with a polymeric outer shell 13. This type of container is
conventional and commonly used for storing hydrogen in gaseous form
at high pressure. It is preferably cylindrical in shape and
provided with an axial opening 17. The liner 15 is usually made of
aluminium whereas its outer shell is made of a composite material
reinforced with carbon fibers. In practice, the container of the
hybrid tank 11 is intended to be used for storing hydrogen in
gaseous form at a pressure usually higher than 40 bar and
simultaneously to receive and store a metal hydride in order to
store hydrogen in solid form as well.
[0070] At least one heat pipe 19 is mounted within the container to
allow the circulation of a heat carrying fluid within the container
11. As shown, the tank 11 preferably comprises only one heat pipe
19 which is inserted into the container through the opening 17 and
extends axially within the same. The tank 11 further comprises a
heat exchanger located within the container to ensure thermal
connection between the heat pipe 19 and the hydride. This heat
exchanger preferably consists of at least one metallic grid, or a
porous metallic structure or fibers 21 which extends transversally
within the container and is in direct contact with the axial heat
pipe 19, the metal liner wall 15 of the container, and the hydride
stored within the same.
[0071] The use of such a system of heat pipe and heat exchanger to
operate a metal hydride is already known (see, for example, U.S.
Pat. No. 6,015,041 granted in 2000 in the name of WESTINGHOUSE
SAVANNAH RIVER CO). In the present case, the invention essentially
lies in that the incorporation of such a system into a tank used so
far only for storing hydrogen in a gaseous form at high pressure in
order to benefit from the advantages of both technologies
simultaneously.
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