in micro-cylindrical arrays

FIELD OF THE INVENTION

The present invention relates generally to fuel storage, and in particular, to accumulation, storage and liberation of hydrogen gas.

BACKGROUND OF THE INVENTION

It is well-known that hydrogen is a very high energy density element and clean- burning fuel. Hydrogen can be combined with oxygen through combustion, or through a fuel cell mediated oxidation/reduction reactions, to produce heat, or electrical power. The primary product of this reaction is water, which is non-polluting and can be recycled to regenerate hydrogen and oxygen.

Currently, hydrogen energetics is the focus of interest in the nuclear industry, motor transport, the auto industry, the chemical industry, the aerospace industry, etc. In particular, the transport sector is a consumer of about half of the world's crude oil production. Moreover, in large metropolitan agglomerations worldwide, road traffic represents one of the most important and fastest growing emission sources for both pollutants and noise. Hydrogen as a new vehicle fuel provides the opportunity for both the reduction or avoidance of polluting emissions, and the drastic reduction of the noise level produced by the vehicles.

One of the hurdles facing hydrogen energetics is safe storage and delivery of hydrogen fuel to a combustion cell. Most generally, several approaches have been developed, including physical storage (liquid or compressed hydrogen) and chemical storage (hydrogen absorption in metal hydrides, and hydrogen adsorption in carbon nano-fibers). All these approaches have fundamental limitations in weight and volume capacities of the storage media. It is known that compressed hydrogen can be safely stored in microcapsules, such as hollow glass microspherical and/or microcylindrical (multi-capillary) arrays. If heated, the glass permeability to hydrogen will increase. Hydrogen can diffuse into the hollow cores of the microspheres and/or microcylinders through the thin glass walls at a rate strongly depending upon the wall temperature. This provides the ability to fill the microcapsules with gas by placing the microspheres and/or microcylinders in high- temperature and high pressure environments. Once cooled, the microcapsules lock the hydrogen inside, since the diffusion rate is drastically lower at room temperature. A subsequent increase in temperature will increase the diffusion rate. Thus, the hydrogen trapped in the microcapsules can be released by subsequently increasing the temperature.

SUMMARY OF THE INVENTION

One of the problems associated with liberation of compressed hydrogen by diffusion is associated with a relatively low rate of temperature induced hydrogen release from the microcapsules. In particular, in order to release gas from microcapsules at a practically useful rate, the activation energy for permeability through the glass should exceed 57 kJ/mol. Moreover, the cross-sectional dimension of the microcapsules should preferably be smaller than about 80 microns. For example, industrial borosilicate glasses should be heated over 600 °C to obtain the required hydrogen liberation rate. As a result of the heating, the pressure inside the microcapsules can be increased, while the tensile strength of glass can be decreased, when compared to microcapsules under normal conditions. Both these factors may cause breakage of the microcapsules.

On the other hand, when the liberation of compressed hydrogen from the microcapsules is carried out with a mechanical opener, the microcapsules are destroyed during operation. In this case, the cartridge can only be expandable, and must be replaced without possibility of refilling.

Accordingly, there is still a need in the art for further improvement of the technique for accumulation and storage of hydrogen in order to provide a more effective hydrogen load and liberation, which will result in increased safety and cost-saving.

It would also be advantageous to have an apparatus for storage and liberation of compressed hydrogen gas having a modular structure in which different parts of the apparatus can be easily replaced for adapting the apparatus to any particular application.

According to one general aspect, the present invention partially eliminates disadvantages of the prior art techniques and provides a novel apparatus for storage and liberation of compressed hydrogen gas. The apparatus comprises a storage tank, a pre- volume chamber coupled to the storage tank, a hydrogen liberating tool, and an adapter module coupled to the pre-volume chamber and configured for coupling the pre-volume chamber to a device utilizing the hydrogen gas stored in the storage tank for supplying the hydrogen gas thereto.

The storage tank comprises a plurality of arrays of hollow micro-cylinders defining cavities storing compressed hydrogen gas merewithin. Each micro-cylinder has an end sealed with a plug made of an easily meltable alloy having a melting temperature lower than the melting temperature of the micro-cylinder material. The pre-volume chamber is coupled to the storage tank such that the micro-cylinder ends sealed with the plugs are located within a volume of the pre-volume chamber. The hydrogen liberating tool comprises a plurality of heating coils wound around the micro-cylinder ends sealed with plugs. The heating coils are configured for melting the plugs, thereby to controllably liberate the hydrogen gas from the arrays of the micro-cylinders into the pre-volume chamber.

According to an embodiment, the apparatus comprises a control system operatively coupled to the hydrogen liberating tool, and configured for controlling operation thereof. The liberating tool includes a controllable power source coupled to the control system.

According to an embodiment, the control system includes a pressure sensor and a temperature sensor. The pressure sensor is arranged in the pre-volume chamber and is configured for producing a pressure sensor signal representative of the hydrogen gas pressure in the pre-volume chamber. The temperature sensor is arranged in the vicinity of the micro-cylinder ends sealed with plugs. The temperature sensor is configured for measuring a temperature in the vicinity of the micro-cylinder ends, and producing a temperature sensor signal indicative of the temperature thereof. The control system is operatively coupled to the pressure sensor and to the temperature sensor, and is responsive to the pressure sensor signal and to the temperature sensor signal. The control system is capable of generating control signals for controlling the operation of the controllable power source.

According to an embodiment, ends of the micro-cylinders distal to the pre- volume chamber are permanently sealed.

According to an embodiment, the external diameter of the micro-cylinders is in the range of 1 micrometer to 400 micrometers.

According to an embodiment, a number of the micro-cylinders in one array is in the range of 50 to 500.

According to an embodiment, the micro-cylinders are made of a material that meets the following condition σ/ρ≥ 1700 MPa cm ³ /g, where σ is the tensile strength and p is the mass density.

According to an embodiment, the easily meltable alloy of the plugs is at least one alloy selected from Sni ₆ Pb ₃₂ Bi ₅ 2, SnBi ₅₈ and Snh 52.

According to an embodiment, the pressure of the hydrogen stored within the micro-cylinders is in the range of 1000 arm - 3000 atm.

According to an embodiment, the pressure of the hydrogen within the pre- volume chamber is in the range of 5 atm - 20 atm.

According to an embodiment, the micro-cylinders have tapering portions in the form of a cone at the ends sealed with a plug, thereby to prevent the pushing of the plugs out from the ends by the highly pressurized hydrogen gas stored in the cavities of the micro-cylinders.

According to an embodiment, the heating coils are coupled to the controllable power source through a connecting line including a female connector which extends from the storage tank into the pre-volume chamber where it meets with a male connector extending from the adapter module.

According to an embodiment, the storage tank comprises a housing for enveloping the arrays of the micro-cylinders.

According to an embodiment, the device utilizing the hydrogen gas stored in the storage tank is a hydrogen fuel cell.

The apparatus itself demonstrates the flexibility of the technology allowing for the open scaling of arrays- in size, length and number; easy linkage to a variety of fuel cells and for the simple shaping of the device using a moldable polymer overwrap for the housing.

The storage capacity is mainly influenced by the capillary parameters itself. These capillaries and finally the arrays are the heart of the system. There are nearly no limitations for the dimensions of the capillaries and the arrays, but some details do strongly influencing the pressure resistance of the capillaries (inner and outer diameters, wall thickness) and therefore the operating pressures and storage capacities. It is of great importance to find the best parameters regarding capillary dimensions (hydrogen storage itself) and array dimensions (optimal heat transfer to melt the stopper alloy) also considering the economical aspect of manufacturing these capillary arrays.

The apparatus of the application does not require additional bulky or heavy equipment, such as a pressure reducer, to ensure its safe and efficient use .The separated gas volumes further ensure the safety of the device. The apparatus requires no rare metals and heavy metals, which ensures a cheaper cost while maintaining the required strength and reducing the weight of the device. The glass used in the apparatus is not only comparably equal in strength to steel but is also much lighter. Furthermore, the diffusion rate through glass is significantly lower than that of steel or composite materials.

The apparatus of the application is able to present the potential and functionality of the new storage system. The various uses of this storage system can be optimized in many ways to achieve the most economical system for a variety of applications, including those of the:

Transport industries - automotive, aircraft/aerospace, ships, maritime vessels, submarines, trucks, rails;

Electronic industries - communications, defense industry, electric and power applications - mobiles, computers, laptops etc.;

Manufacturing industries - fiber materials, containers;

Infrastructural projects - large and bulk storage, stations.

There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows hereinafter may be better understood, and the present contribution to the art may be better appreciated. Additional details and advantages of the invention will be set forth in the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

Fig. 1A is an exploded view of an apparatus for storage and liberation of hydrogen gas, according to one embodiment of the present invention;

Fig. IB is a schematic longitudinal cross-sectional view of the apparatus shown in Fig. 1 A, according to one embodiment of the present invention;

Fig. 2 is a view of a storage tank of the apparatus shown in Figs. 1 A and IB from the end proximal to the pre-volume chamber, according to one embodiment of the present invention;

Fig. 3 is a view of an array of micro-capillaries of the storage tank shown in Fig. 2, according to one embodiment of the present invention; and

Fig. 4 is a view of the adapter module of the apparatus shown in Figs. 1A and IB from the end proximal to the pre-volume chamber, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The principles and operation of an apparatus for storage hydrogen gas according to the present invention may be better understood with reference to the drawings and the accompanying description. It should be understood that these drawings are given for illustrative purposes only and are not meant to be limiting. It should be noted that the figures illustrating various examples of the apparatus of the present invention are not to scale, and are not in proportion, for purposes of clarity. It should be noted that the blocks as well other elements in these figures are intended as functional entities only, such that the functional relationships between the entities are shown, rather than any physical connections and/or physical relationships. The same reference numerals and alphabetic characters will be utilized for identifying those components which are common in the hydrogen storage apparatus and its components shown in the drawings throughout the present description of the invention.

Referring to Fig. 1A and IB, an exploded view and a schematic longitudinal cross-sectional view of an apparatus 10 for storage and liberation of hydrogen gas is illustrated, respectively, according to one embodiment of the present invention.

The apparatus 10 for storage and liberation of compressed hydrogen gas has a modular structure in which different parts of the apparatus can be easily replaced for adapting the apparatus to any particular application. The apparatus 10 comprises a storage tank module 11, a pre-volume chamber 12 coupled to the storage tank module 11 using a sleeve 16a, and an adapter module 13 coupled to the pre-volume chamber 12 using a sleeve 16b.

The apparatus 10 also includes a hydrogen liberating tool 14, and a control system 15 operatively coupled to the hydrogen liberating tool and configured for controlling operation thereof.

As shown in Fig. IB, the storage tank 11 comprises a housing 111 including a plurality of arrays of closely packed hollow micro-cylinders (micro-capillaries) 112.

The housing 111 envelops the arrays of the micro-cylinders 112. The shape of the housing 111 can, for example, be tubular. However, it should be understood that generally, any desired shape of the housing can be used. The housing can be constructed of a suitable metal, polymer (e.g., polytetrafluoroethylene) or composite material with thickness of the walls appropriate to hold the arrays together. The housing 111 also acts as a protective shell against mechanical damages of the micro-cylinders 112, and allows for a flexible design of the storage tank 11. When desired, the inner surface of the housing wall can be bound to the peripheral micro-cylinders.

Although three arrays of hollow micro-cylinders are shown in Fig. IB, generally the storage tank module 11 can comprise any desired number of the arrays. The micro- cylinders 112 define cavities in which the compressed hydrogen gas can be trapped. The micro-cylinders 112 in the array structures can have any desired shape in their cross- section and be closely (intimately) packed. Examples of the cross-section shape include, but are not limited to, circular, oval, polygonal, hexagonal, etc. It should be understood that when the cross-section shape is hexagonal, the closest packing of the micro- cylinders can be obtained.

Preferably, but not mandatory, the micro-cylinders 112 in array structures are bound together to form a rigid structure. For example, the micro-cylinders 112 can be tied with a fastener (not shown), e.g., girded with a fastening band. Likewise, when the micro-cylinders are made of glass, aramid or metal, they can be bound together, for example, by welding, brazing and/or sintering. Moreover, an adhesive material, e.g., epoxy adhesives, can also be used for binding the micro-cylinders together.

Ends 114 of the micro-cylinders 112 (distal to the pre-volume chamber 12) are permanently sealed, e.g., capped on the ends by semi-spheres with comparable wall thickness. Other ends 115 of the micro-cylinders 112 (proximal to the pre-volume chamber 12) can be either open or sealed with plugs 113. The micro-cylinder ends 115 sealed with the plugs 113 are located within a volume of the pre-volume chamber 12. A pictorial view of the storage tank 11 of the apparatus 10 shown in Fig. IB from the ends 115 is shown in Fig. 2.

In particular, the ends 115 can be open when the cartridge is not filled with compressed hydrogen, to enable free penetration of hydrogen inside the cavities. After the filling of the micro-cylinders with compressed hydrogen gas, the ends are sealed with the plugs 113.

It should be understood that the module structure of the apparatus provides the possibility to detach the storage tank module 11 from the pre-volume chamber 12 for placing the storage tank module 11 into an autoclave (not shown) for filling the micro- cylinders 112 with hydrogen gas.

The micro-cylinders 112 are made of a material having high tensile strength σ and low mass density/?. For example, materials that meet the condition σ/ρ≥ 1700 MPa cm ³ /g are suitable for the micro-cylinders. Examples of materials suitable for the micro-cylinders 112 include, but are not limited to, borosilicate glass, MgAISi glass, S-2 Glass™, R-glass available from Saint-Gobain Vetrotex Textiles, T- Glass available from Nitto Boseki Co., Ltd. (Nittobo), fused quartz, polymers (e.g., Kevlar™, Twaron™), etc.

Generally, the micro-cylinders 112 can have any desired length. In turn, the external diameter d of the micro-cylinders 112 can be in the range of about 1 micrometer to about 400 micrometers. A number of the micro-cylinders 112 in one array can, for example, be in the range of 50 to 500. These dimensions of the capillaries are strongly dependent on pressure resistance, hydrogen diffusion, possibility of easy manufacturing etc. whereas the dimensions of the arrays are dependent on the manufacturing process, opening procedure and the real application. When desired, the - Si - micro-cylinders 112 can have tapering portions (not shown) in the form of a cone at the ends 115 sealed with plugs 113, in order to prevent the pushing of the plugs out from the ends by the highly pressurized hydrogen gas stored in the cavities of the micro- cylinders.

Methods for fabrication of hollow microcylinders and microcylindrical array structutres are known per se. In particular, various microcylindrical (capillary) arrays made from glass and/or plastics are widely used in x-ray optics and photonics. Generally, the process of fabrication of microcylindrical arrays is divided into three main stages: (i) drawing capillaries with relatively large diameter, (ii) re-drawing them into a bundle of capillaries with smaller diameter, and (iii) sintering capillaries into the array. Existing technology enables one to produce vast arrays with a capillary diameter down to 1 micron or even less, and a wall thickness-to-diameter ratio less than 5%. For example, capillary arrays suitable for the purpose of the present invention can be obtained from Paradigm Optics, Inc.; 9600 NE 126th Ave, Suite 2540 Vancouver, WA 98682 USA; Hilgenberg GmbH, Strauchgraben 2, D-34323 Malsfeld, Germany; etc.

The hydrogen liberating tool 14 is configured for controllable liberating hydrogen gas from the storage tank 11 in which hydrogen is stored in the micro- cylinders 112 at very high pressures into the pre- volume chamber 12 coupled to the storage tank 11 in which the hydrogen is stored at a moderate pressure. For example, the pressure of the hydrogen stored within the micro-cylinders 112 can be higher than 1000 atm (e.g., in the range of 1000 atm - 3000 arm), whereas the pressure of the hydrogen within the pre-volume chamber 12 can be in the range of 5 atm-20 atm. Such pressure can, for example, be needed for the operation of a hydrogen fuel cell.

For measuring pressure of the hydrogen within the pre-volume chamber 12 the control system 15 can include a pressure sensor 152 that is operable for producing a gas pressure sensor signal. The pressure sensor can be coupled to the control system 15 which can be arranged outside of the pre-volume chamber 12. The control system 15 can, inter alia, be responsive to the gas pressure sensor signal and be capable of generating a control signal to the hydrogen liberating tool 14 for controllable liberation of the compressed hydrogen gas from the micro-cylinder arrays into the pre-volume chamber 12 when the pressure in the pre-volume chamber drops below a certain value, e.g., 1.5 atm. According to the embodiment shown in Figs. 1A, IB and 2, the liberating tool 14 includes a controllable power source 144 coupled to the control system 15 and a plurality of heating coils 141 made from wires wound around the ends of micro- cylinders 112 that can be sealed with plugs 113. The coils 141 create heating jackets around each array of the micro-cylinders 112. The heating coils 141 are coupled to the controllable power source through a connecting line (143 in Fig. IB). As shown in Figs. 1A and 2, the connecting line between the heating coils 141 and the controllable power source includes a female connector 142 which extends from the housing 111 into the pre-volume chamber 12 where it meets with a male connector 132 extending from a housing 134 of the adapter module 13.

The liberating tool 14 can use a temperature sensor 151 associated with the control system 15, and arranged in the vicinity of the heating coils 141. The temperature sensor 151 can be configured for measuring temperature of the micro-cylinders 112 in the vicinity of the ends 115 that are sealed with plugs 113, and producing a temperature sensor signal indicative of this temperature. The temperature sensor 151 can be coupled to the control system 15 which is, inter alia, responsive to the temperature sensor signal and capable of providing control of the controllable power source. Such control is achieved by providing a required electric power to the heating coils 141 to obtain a temperature required for melting the plugs, and thereby opening the corresponding micro-cylinders 112. Care should be taken in order to avoid overheating and damaging the cartridge elements.

The plugs 113 should preferably be made of an easily meltable alloy having good enough adhesion to glass. Specifically, a melting temperature of this alloy must be lower than the working temperature of the micro-cylinder material. Examples of alloys suitable for the plugs that are used with borosilicate glass micro-cylinders include, but are not limited to, Bi52 Pb32Sn, Bi58Sn and In52Sn.

Liberation of hydrogen from the sealed micro-cylinders 112 can, for example, be organized in a gradual manner, i.e., by one-by-one heating the sealed ends 146 of the microcylinder arrays above the alloy's melting point, thereby melting the plugs and opening the micro-cylinders 112. In other words, the control system 15 allows for the gradual release of hydrogen, by heating one single micro-cylinder array at a time. Each array is equipped with a heating coil 141 which, when activated, melts the corresponding plug 113 (placed at the end of each capillary) to a liquid state. The pressurized hydrogen gas drives the molten alloy out of the array, allowing for the release of hydrogen into the buffering volume of the pre- volume chamber 12. The buffering volume provides for the controlled release of hydrogen from the capillary arrays over a gradated and specified period of time, providing the required level of hydrogen within a designated pressure range. Here the optimization regarding heat transfer to the complete area is of importance in order to realize the opening of the complete array diameter. If the diameter of the array is too large, only the outer (peripheral) capillaries of the array could be opened when heat is applied, while the inner capillaries are still closed. This would result in an insufficient hydrogen release. In the case of hydrogen release, the temperatures of greater than 160 °C at the ends 115 can be used, that for example, can be achieved by applying electric power in the range of about 0.2 watts - 0.7 watts for about 15 seconds - 20 seconds.

Referring to Figs. IB and Fig. 4 together, as described above, the apparatus 10 also includes the adapter module 13 coupled to the pre- volume chamber 12. The adapter module 13 includes a housing 134 configured for holding a device 131 utilizing the hydrogen stored in the storage tank 11 for its operation. An example of the device 131 includes, but is not limited to, a hydrogen fuel cell. A hydrogen fuel cell converts a hydrogen fuel into an electric current. It generates electricity inside a cell through reactions between hydrogen and an oxidant (for example, oxygen from air), triggered in the presence of an electrolyte. The hydrogen fuel flows into the cell through an opening 133 arranged in the housing 134 at the end coupled to the pre-volume chamber 12, whereas oxygen flows from air from an opening (135 in Figs. IB) arranged in the lateral side of the adapter module 13. The hydrogen fuel cell can operate continuously as long as the necessary reactant and oxidant flows are maintained. The electric voltage generated by the hydrogen fuel cell 131 can be provided to the terminals 136 which can extend from the housing 134 at any desired place.

As shown in Figs. 1A and IB, the hydrogen fuel cell 131 is placed inside the adapter module 13; however other configurations of coupling the hydrogen fuel cell to the pre-volume chamber 12 are also contemplated. Accordingly, the adapter module 13 can have any desired configuration, depending on the fuel cell.

As such, those skilled in the art to which the present invention pertains, can appreciate that while the present invention has been described in terms of preferred embodiments, the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures systems and processes for carrying out the several purposes of the present invention.

It should be noted that while the present invention has been described for the purpose of storage and liberation of compressed hydrogen gas, the application of the invention is not limited to hydrogen energetics. In the prior art techniques, filling and liberating of hydrogen was based on diffusion of gas through the walls of the storage microcapsules. Since the diffusion rate of gases other than hydrogen and helium is negligibly low at any reasonable temperatures, such prior art techniques cannot be used for storage and liberation of such gases. This limitation of the prior art techniques is not applicable to present invention, since diffusion through the walls is not used in the apparatus of the present invention.

Accordingly, the storage tank of the apparatus of the present invention can be used for storage and liberation of gases other than hydrogen, e.g. methane, oxygen and so on.

It is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

It is important, therefore, that the scope of the invention is not construed as being limited by the illustrative embodiments set forth herein. Other variations are possible within the scope of the present invention as defined in the appended claims. Other combinations and sub-combinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to different combinations or directed to the same combinations, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the present description.