CA2452067A1

CA2452067A1 - Method for storing hydrogen in a hybrid form

Info

Publication number: CA2452067A1
Application number: CA002452067A
Authority: CA
Inventors: Robert Schulz; Guoxian Liang; Jacques Huot; Patrick Larochelle
Original assignee: Individual
Current assignee: Hera Hydrogen Storage Systems Inc
Priority date: 2001-06-29
Filing date: 2002-06-28
Publication date: 2003-01-09
Also published as: MXPA03011759A; EP1404611A1; KR20040012993A; JP2004530628A; RU2004101771A; WO2003002451A1; US20030042008A1; CN1522224A; BR0210764A

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 hybride. 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.

Description

METHQD~FUR'ST~'RING=HYIJR'QGEN~IN A HYBRID FURM
FIELD QF'THE'INVENTIDN
The presEnt-inventian-relates-to a m~etho~d for-storing hydnsgen in a hybrid form. More-specifically, it relates-to a method-for-storing hydrogen in two different~fvrms-withiwa-single tank.
The invention-also-relates~to-tanks-hereirrafter-called "hybrid tanks", which are-specially adapted~for-carrying-out-the~atrove-mEthod when-the hydrogen is stored in liquid acrd-solid-forms-arrd-whEn-the hydrogen is stored in solid and gaseous-forms, respectively.
to BRIEF'DES~C'RIPTIDN'QF'THEvPRIOR ART
Methods far staring hydrogEn can be classified in three main categories (A) gaseous-storage in-high-pressure~tanks ;
(B) liquid storage in-cryogenic~tanks ; and (C)solid-storage irrtanks-containingmaterials-that-absorb (in-volume) or adsorb (owsurface) hydrogen.
The last-category IisteWabove as-category (C) is the one that makes use of metal hydride-storage tanks.

2 o Each ofthe-above-categories-has~advantages~arrd disadvantagesthat are summarized in-the-following Table I

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By wayof-exarnple, 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-pressunzs-indicated in Table II
TABLE II
Gaseous~storage Hydrogem-pressure Am~amtt-vf-hydrvgemwithimorre 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 prig (1,035 bar) 0.0512 kg In the case of a method for-storirrg hydrogen in a liquid farm (category B), a-tank of-arre (1 ) liter~will contain 0.0708 kg-of hydmgen-since the 1 o density of liquid hydrogen at -252.8°C (thatis-at-the-conventional boiling point of hydrogen) is equal to 0.0708 kg/I.
Last~of all, in-the-case-of~a-methad-for-storntg hydrogen in a solid form with a metal hydride (category C), a tank of one (1 ) liter containing a hydride of formula ABS like LaNi5H6 (density: 6.59 kg/I, hydnJgen storage 15 capacity -1.4%) occupying-all thevolume-of~thE-tank, will contain 0.0923 kg of hydn~gen, that-is-almost~twice-the=amount-ofihydrogEmstored in a gaseous form in a tank of one liter~at 15,000 psig.
The results-of-this-comparative-example are given in Table III

TABLE III
Carnprarisom-~of-thE-storage-capra~iiy-vf'the-thru-trasic s m~ethods-fvrstvrirrg~hydro~gen Method Amourrt-of'hydrvgen-stvred-within a tank of vrre liter (A) Gaseous storage-at 15,000 psig 0.0512 kg (1,035 bar) at'ambient-temperature (B) Liquid storage at -252.8C0.0708 kg (1 bar) (C) Solid storage in'afiydride of LaNiS

0.0923 kg (10 bar) at-ambient-temperature Of course, in the case of'thwmeth~d for-starirrg'hydragen in a liquid form (category B), there-is-always-somE-gaseous~hydrogen-in-equilibrium with-the liquid because-of-some=evapvration-af-the latter. Also, iwthe case of the 1o method far-storirTg-hydragen-in-a-solid-form-with a-metal hydride (category C) typically oae'ratirrg-at-low- ressure (10 bar), there is same gaseous hydrogen because-tire-hydride-neveroccupies-all the-space-in-the'tank. Moreover, in the case of the method far-staring-hydragen in a gaseous farm at a very high pressure (category A), there is always'same hydnzgemthat is adsorbed (such is adsartred hydn~gen is also called "solid hydn~gEn" according to the above terminology) anto'the-internal walls-of-the-tank. TherEfore, in each-method listed hereinabove (gaseous, liquid anti solid), there is ~Iways a small amount of hydnzgen-that is stand-accordirrg-to arrother-methad of~storage.
By way afExample, one-mayevaluate'the-maximum-percentage of 2 o hydrogemth~at'may'come-fram°arrothermethad of'starage in-the case of a tank of one liter containing a -metal hydride powder (LaNisHs). Assuming that the powder is'not~campacted and, thErefare, occupies about half of-the volume of the tank, that is abaufihalf a-liter, corrsidering'also'that'the density of LaNiSHg is equal to 6.59 kg/l arrd furttrer-assuming-that'the-gaseuus hydnsgen within the tank (about half a liter) is at-a~pn~ssure 10 bar, the-amount of hydrogen-that is not solid within-the-tank of-ane literwill be as-reparted in Table IV:
TABLE IV
"Gaseous" hydrogen "Solid" hydrogen Total amount of (10 bar) hydrogen 0.00041 kg (0.9%) 0.0462 kg (99.1%) 0.0466 kg (100%) 5 This example-clearlyshows-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 alwaysbe lower-than 5% by weight.
It has already been suggested that there could be some advantages in coupling- different-means for-storing hydnzg~en within a single 1 o category.
By way of example, U.S. patent No. 5,906,792 entitled "Nanocrystallirre-composite-forhydnigewstorage" in-thwname-of~the Applicant and the McGill University, discloses that there are advantages when one combirres 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 erTginE, the low temperature metal hydride allows cold startirrg-of-thE-engine by-providirrg-the, hydrogen at the start up.
When the engine is hot, the heat-that is gernerated by the same permits to induce~thE desorptiowof~hydrogen-frorrrthe~higtrtemperatare-metal hydride (see 2o column 3 ofithis U.S. patent No. 5,906,792 for-more details).
Similarly, international laid-open patent application No. WO
01/16021 published on March 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 olio, the hydrogen absorption and desorption kinetics.
U.S. patent No. 5,872,074 entitled cc Leached nanocrystalline materials, process-far-manufa~cture-thE-samE-and use thenrofiin-the energetic field" in the namE of-the Applicant, also discloses that~the hydrogen sorption kinetics can-be improved-wh-en-use is-made~of~a hydride having high specific surtace.
Indeperrder~tlyof-the above, it is also krrown that~the method (C) for starirng hydrogewin a-solid-form-usually has a-respvnse time (loading and s unloading)much-slawerthan-the-method (A)-for-stvrmg-hydnzg~en in a gaseous form and slower-tharr the -method (B) for storing hydnzgen in a liquid form.
Actually, at least 15 minutES-arrd~semetim~es-more-thsn 1 trour-are-required to fill up a hydride storage-tank. In spite- of-this drawback, the method. for storing hydn7gen in a solid-form-hasuthe-highesficapacity of storage per-volume unit l o (see again Table I I I hereirrabove).
It is known-that-somewtechnical applications require a response time much-fasterthan-ane-minute.
Thus, for~example, in UPS systems (urtintemrptible-pvwersupply) using fuel cells fed with hydrogen, a response time of about one hundred 15 milliseconds is usually-required. Oficourse, a-hydrog~-storirrg~tank using-metal hydride-canrrot~atisfythis-particularnrquirernent. However, in-such a case, use could be made of-a-tank iwwhich~hydrogen is-stQred in a gaseous-form at high pressure.
Similarly, iwhydrogemoperate~d-vehicles, there-are~diffenrnt types 2 0 of transitory-pEriods, like short duration accelerations (second) which usually require a response time of-ab~aut-one- hundred-millisecond-fn~m-the propulsion system;
and power~ir~creases~ whErrthe-vehicle is-climbing up a hill, which may 2 s last a few minutes.
In hybrid vehicles-which~make use-ofia-fuel cell and batteries, the very short accelerations (second) can-betaken care by-the batteries whereas the-transitoryperivdwof-a~lorrger~duration (a~fewminutes) mayrequire hydrogen stored in a gaseous-form. On~thE other hand, the average-power-which is of 3 o about 20 KUU for a typical vehicle, may easily be accomorfated by a metal hydride tank. The energy contained in-the batteries ofisuch a vehicle usually repnrsents-abeut 1 % ofithe=ensrgyon board. Therefore, orre-needs an amount a 3 ,F ~, ~fjfi~ f ,. ;s,i ~ o :v~ ' ~" r,, ~ ~ , .~. -Yt~ 2t ,.
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of hydrogen higher than 1 % to take charge of the trarisitory periods.
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
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. _ The present invention basically consists in coupling and using in a single tank hereinafter called cc hybrid tank for storing hydrogen » at least two of the methods for storing hydrogen mentioned hereinabove, namely A) 'the method far storing hydrogen in a gaseous form ;
B) the method for storing hydrogen in a liquid form ; and G) the method for storing hydrogen in a solid form.
One 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.
2 o More specifically, the invention as claimed hereinafter is directed to a 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 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, with the proviso that : ' each-of the~toring_means_a) to c~ tftat_are used, is sized to store at least 5% by weight of the total amount of hydrogen stored within the tank; and 3 0 when use made of a combination of the storing means a) and c), then said means c) consists of a metal hydride having an equilibrium plateau pressure higher than 40 bar at the operating temperature of the tank.
~1 AMENDED SHEET . ~ 29 01 20QS
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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.
Another object of the present invention is to provide a hybrid tank for storing hydrogen in both liquid and solid forms, comprising two concentric so 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 comrriunication with the inner container. It is not is under vacuum and contains a metal hydride for storing hydrogen in a solid form.
A further object of the present invention is to provide 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 2 o form at a higher pressure and to receive and store a metal hydride in order to ' store hydrogen in solid form; ~ .
- at least one heat pipe mounted within the container to allow circulation of a heat carrying fluid; and - a heat, exchanger located within the container in order to ensure 25 thermal connection between said at least one heat pipe and the hydride.
BRIEF DESCRIPTIf~N C>F THE DRAWINGS
The invention and the way it can be reduced to practice will be better understood-upon~readingrthe-followingmon=limitative-examples-given-with--3 0 reference to the accompanying drawings in which : .
Figure 1 is a diagram illustrating the equilibrium plateau of the hydride used in a hybrid gas-solid storage tank disclosed in example 1 ;
' ' AMENDED SHEET y9 D'1 203:
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Figure 2 is a-schEmatic-cross-sectiartal view of-the hybrid liquid-solid storage-tank disclosed in-example 2 ;
Figure 3 is a diagram illustrating-the equilibrium plateau of the hydride user! in-the-hybrid-gas-solid-storage-tank disclosed in example 3 ;
Figure 4 is-a-sch~ematic-cross-sectional viewvf~thwhybrid gas-solid storage-tank disclo~sEd in~ example 3; and Figures 5 and 6 are-diagramswgivirrg-the~equilibrium plateaux of several hydrides~as-afanctiomof~the-temperature-and irrdicatirrg-which-orre could be used in-the hybrid gas-solid-storage-tank-disclosed in examples 1 and 3.
EXAMPLE 1: Hyb~ri~d~stara~ge-tank-fvr-storirrg-hydrvg~e~min gas and-solid-farms A hydrogen-storage~tankhaving-avolume of 1 liter~has-beerrfilled up with a powder-ofy articles of a hydride of LaNiS having an average diameter~of 5 nanometers. Thw powderoccupied 5p% by volume of the tank, that is 0.5 liter, sirrce-it~was-rrot~compacted. ThE-number~of-atoms-on-the surface of these nanoparticles-represented about 28% of the total amount of atoms within-each~particle-corrsidering~a layer~of 0.4-to 0.5 rranometervwthe surface of each-narroparticle. The-tank-has-thewbeemfilled-up-with-gaseous hydnzgen at 2 o different-pnrssures-rarrgirng-from 10 bar (typical pn~ssure of use of the metal hydride tanks) to 700 bars (typical pressure used in high pressure gaseous tanks). It was assumed-that-the-amount-ofihydrogen in the volume and at the surface of the metal hydride- corresponded to HIM=1 (H = hydrogen, M =
metal), which is typical to- most-metal hydrides. Under-these conditions, the 2 5 ameunts of hydrogen-assaciaterl-to-the-two-different~means ofistorage-that were used, have been-calculated-and-are-n=ported in Table V hereinafter TABLE V
HydrogenHydrogen % Hydrogen % Hydrogen % Total amount in bound of pressuregaseous-phase connected inserted hydrogen to the within (kg) within (kg) surface of the hydride the the tank hydride 10 bar 0.0004 1 0.0142 280.0365 710.0511 *

150 psi 248 bar 0.0089 150.0142 240.0365 610.0596 psi 345 bar 0.0117 190.0142 230.0365 580.0624 psi 690 bar 0.0196 280.0142 200.0365 520.0703 psi It is worth-n~oting-that-iwthE-first-case reported in Table V, that is 5 when the-pressure-is-of 150 psi (10 bar), the amount of-hydrogen in gaseous phasewrepresented about 1 % ofithe-total amount. This example is illustrative of what is-pn~Ently~obtainEd in conventiunal-metal hydride-tanks-and is therefore outside the scope-of-the-present-invention. However, in the-threE other-cases reported hereirratrove where-thewpressures-were of 3,600 psi, 5,000 psi and l0 10,000 psi, the-amounts-of-hydro~g~rin-gaseous~phase~represented about 15%, 19% and 28% respectively-of-thE-total amDUnt-of~hydn~gen-withiwthe~tank. Such is much highsr~thamthE limit-of 5% as indicated hereinabove.
The-tankdisclosed-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 gerreratar. In the case -of-a failure of-the elecfic-supply, the hydrogen in the gaseous phase~will initially-supply the fuel cell orthe generatar-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 AB5 alloy at room temperature, there will be almost rro more hydrogen in the 2 o 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.
It is worth-noting-that, in-this example, the equilibrium plateau of LaNi5 which is a cQnventiQrral low-terrrperatare-metal hydride at-the operating temperature (typically-rangirrg-between 0 to 100°C), is slightly higherthan the pressure offiydragen~quiretdatth~inlet~ofthe~fuel cell, which-typically about bars. If the-tankcontairrs~50% by volume ofhydride-arrd the balance is occupied with gasevus~hydrQgerrat 690 bars (10,000 psi), the situatiomwill correspond to that of-the-diagranrgivemin Figure 1.
Urrder-such a-circumstarrce, during-operation of-the system, the hydrogen will come~first~from-the-gaseous~phase. Then, when the amount of hydrogen anti the gas pressure became low, the hydride will take over by 1 o providirng-hydroge~rrto-the-system. The-pressure--withirrthe-tankwill then be kept at the level of-the-desarptiomplateau ofithe-hydride. The kinetics of-the system will therefore be quite high at-the beginning (n~pvnse time of the gaseous system) acrd-thereafter~low(response-timE-of~the-hydride system).
There are also ~other-advantages~ in using such a hybrid method i5 combining-gas-arrd-solid-storage. In-particular, orre can-mention a) refillirrgwpyof~thwtank is-carried~oufiiwa~short~timE~as-compared to converrtianal-metal-hydride-tanks ;
b) the design of-the heat -transfer components of the tank is simplified ; and 2 o c) the high-storage-capacity by-volurrte of-the mEtal hydride and the high capacityof-storage-by-weight-ofithe-rrew-composite high-pressure gas storage-tanks~arre-combined.
EXAMPLE 2 : Hybrid-tarrk-for-sfiaririgydrogetfirr liquid-artd~solid-forms A hybrid~tank 1 for-storirrg~hydn~gen-having a total volume of one liter has been-devised-from~two-cortcentric~cantainers 3,5 (see Fig. 2). The inner container 3 had a volume of 0.8 literwhereas the outer container 5 had a volume of 0.2 liter. Arrinsulating-sleeve 7 was-positioned between-the inner and 3 o the outer-containers 3,5 to ke-ep-the inrrercontairrer 3 at low-temperature.
In use, the irmercontairrer 3 ofthe~tank 1 was filled up with liquid hydrogen. It contained~about 0.07D8 kg/I x 0.8 liter= 0.0566 kg of hydrogen.
The outercontainer-5 wasfilled-with-a-powderof~a~metal hydride vf~the-type LaNi5He which occupied-about~5D% of-the-volume, thafiis about 0.1 liter. Therefore, the outer-cantainer~5 contained 6.59 kg/I x 0.1 liter~x 1.4% = 0.0092 kg of hydrogen.
The total arrrount-of-hydn~gen-stored-within the-tank 1 was equal to 0.0658 kg (14% in the outertank arrd 86% in-the-inner-tank).
As compared~to-a-canverttiorral~tankfor~sto~ring-hydrogen in a liquid form, the tank disclosed-in-example 2 has-the-arivantage of having no loss of hydrogen overa~pEri~d-that-may-exceed-two-weeks. Indeed, the problem with any conventional liquid-hydrogen-storage~tank is~that-the hydn~gen evaporates l o (boil off). Up to 1 % of-the amount of liquid-hydn~gew 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-bail-offfiydnJgen-is-atrsvrbed by the~metal hydride that extends in-periphery~of~the-irnlercontainer-arrdvp to its-maximum-capacity (that is 0.0092 kg/0.0006 kg/day-= 15 days).
It is worth noting that the idea of using metal hydrides for "catching" evaporated-hydrogewfn~m-a liquid~hydnzgerrstorage~tank has already been suggested, but by mearrs of two separate systems that must be interrelated, coTmecte~d -artd independently controlled. In this regard, one can refer to U.S. patent No. 5,728,483 to SANYO-ELECTRIC CO. In contrast, in the 2 o present invention, these'two-diffen~rtt-means-forstoring-hydn~gemare-combined within a single-tank-arrd-therefore-operate-in-a~simplermarrner.
EXAMPLE 3 : Hybrid-tank-for-stvring~hydra~gemin-ga~s=solid form for-usw in-a-system-havirrg-tra~rtaitvry-periods In the tank-disclosed in example 1, use was made of LaNiSHe as the hydride. This compound is knUWn-to have a low equilibrium plateau (viz.
lowerthan 40 bar) at~aperatinytemperature. Use could also have beam made of other hydride with-a low equilibrium-plateau, such as NaAIH4, LiAIH4 or MgH2.
3 o AccQrdirrg ta-the invention, it is however-possible to use also a hydride havirng an equilibrium plateau that is much higher at the operating temperature (typically -ranging between 0° and 100°C) than the equilibrium plateau of-the carrventional hydrides (typically-rarrglng bEtween 1 to 10 bar).
Such a high equilibrium plateau is 40 bar ar- higher . An example of such hydrides is TiCr~,$ which-has-an-equilibrium-plateawat-nwm-te~mperature-much higherthan 100 bars (see Fig. 6). There=are~also-metliurrrtemperature hydrides s with equilibrium-plateau-at-high-pressures, like TiMnz_y, Hf2Cu, Zr2Pd, TiCu3 or Vo.sss Cr0.145 which cawb~e-of-interest~farthis-kir~twf~application (see Figs.

and 6).
Under-these-circumstar~es, when-there is awEed for-hydrvgen, the gaseous system of-the starage~ tank will pemrrit-to accommodate such a 1 o request with a very-shrarrtresporrse-time (t1 ) of-atroutorte-second (farexample in the case of-a carthat-accelerates). When-thgpre~ure-withirrthe-tank dn~ps and changes from~a value (1 ) to-a value (2) (see Fig. 3), the hydridE~will m~generate the gaseous system-with-a~lower-respanse~time (t2) of a-few-minutes, until the next acceleration.
is This hybrid-metlrorl-makes it~pussible-to-substantially simplify the structural compvn~ents -n:~quired for' heat tr~rrsfer in order to induce the desurptiowfn~nrthe-hydride-orabsvrptiowthErein. Mprevver, this-hybrid method perrrrits, thanks~to-thwhigh-pressure, to solve-the-problem of-refillirrg hydrides such as-thE alanates (NaAIH4 orLiAIH4). As~to-the kind of-hydrides-that can be z o used, referernce-can-bgmade-to Figure 5 (hydrides-of-the AB5 type) and Figure 6 (hydrides of-the ~AB2 typE) en~closed-herewith.
As an example of the way this method could be carried out, refererrce caw be-made-to Figure 4 which-shows a hybrid tank 11 for storing hydnzgen in both-sDlid-and~gase~ous~farm. Thewtank 11 corrrprises a container 25 having a metallic linet--or-inrrerwall 15 covered-with a polymeric outer-shell 13.
This type of-cvntaineris-conventiorral~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-sh811 is-made ofa compasite-material reinforced with carbon 3 o fibers. In practice, the-cantainer~of-thE-hybrid-tank 11 is-intended to be used for storing hydrc~gEn-in-gaseous-fomrat-a-pressure usually highEr-than 40 bar and simultarre~ouslyta-receive=arrd-stare=a-metalfiydride~in-arderta-stare-hydmgen in solid farm as well.
At least-one~hEat-pip~e 19 is~mounted withirrthe-containerto allow the circulation-af-a-heat-canyirrg-fluid~withirrthE-cantairrer11. As-shown, the tank s 11 preferably comprises only orre heat pipe 19 which is inserted into the contairrerthrouglrthE~apening 17 a d~exterrds-axially withiwthE~same. The tank 11 further-comprises a-heat-exchanger-located-within-the cantainerto ensure themral cannECtian between the heat pipe 19 and the hydride. This heat excharTgerpnrferably-consists-of-at-least-ane~retallic~grid, or-a-pvrous metallic t o structure-or-fibers 21 which-exterrds-transversally withirrthe container and is in dire~ctwantact~with-the-axial-heat-pipe 19, the-metal lir~erwall 15 of the container, and the hydride-stonrd-within-the-same.
The use of such a -system of heat-pipE and heat exchanger to operate a-metal hydride is already known (see, farexample, U.S. patent No.
15 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 incarp~aratian-afisuch-a-system-into-a-tankused sa-far~anly farstoring hydrogen in a gaseous famrat~high-pressure in-orderto- b~ensfit-fnzm-the-advantages of both te~chrrolagies-simultarreously.

Claims

15

1. A method for storing hydrogen in a hybrid form, characterized in that it comprises 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, with the proviso that:
each of the storing means a) to c) that are used, is sized to store at least 5% by weight of the total amount of hydrogen stored within the tank, and when use is made of a combination of the storing means a) and c), then said means c) consists of a metal hydride having an equilibrium plateau pressure higher than 40 bar at the operating temperature of the tank.

2. The method according to claim 1, characterized in that:
use is made of a combination of said storing means a) and c), and said storing means c) consists of a Ti- or alanate (AlH x) based hydride.

3. The method according to claim 1, characterized in that:
use is made of a combination of said storing means b) and c), and said means c) consists of a metal hydride.

4. A hybrid tank for storing hydrogen in both liquid and solid forms, characterized in that it comprises 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 communication with the inner container, being not under vacuum and containing a metal hydride for storing hydrogen in a solid form.

5. The hybrid tank according to claim 4, characterized in that the hydride that is used within the outer container is an hydride having low equilibrium plateau pressure at the operating temperature of the tank.

6. The hybrid tank according to claim 5, characterized in that the hydride that is used within the outer container is selected from the group consisting of NaAlH4, LiAlH4, LaNi5H6 and MgH2.

7. The hybrid tank according to claim 4, characterized in that the hydride within the outer container is an hydride having a high equilibrium plateau pressure at the operating temperature of the tank.

8. The hybrid tank according to claim 7, characterized in that the hydride that is used within the outer container is selected from the group consisting of TiCr1.8, TiMn2-y, .Hf2Cu, Zr2Pd, TiCu3 and V0.855 Cr0.145.

9. A hybrid tank for storing hydrogen in both solid and gaseous forms, characterized in that it comprises:
- 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.

10. The hybrid tank according to claim 9, characterized in that:
- 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.

11. The hybrid tank according to claim 9 or 10, characterized in that the hydride that is used in the container is an hydride having low equilibrium plateau pressure at the operating temperature of the tank.

12. The hybrid tank according to claim 11, characterized in that the hydride that is used in the container is selected from the group consisting of NaAlH4, LiAlH4, LaNi5H6 and MgH2.

13. The hybrid tank according to claim 9 or 10, characterized in that the hydride in the container is an hydride having a high equilibrium plateau pressure at the operating temperature of the tank.

14. The hybrid tank according to claim 13, characterized in that the hydride that is used in the container is selected from the group consisting of TiCr1.8, TiMn2-y, Hf2Cu, Zr2Pd, TiCu3 and V0.855 Cr0.145.