Receptacles – Rigid heat transfer container
Reexamination Certificate
2002-02-21
2003-09-30
Cronin, Stephen K. (Department: 3727)
Receptacles
Rigid heat transfer container
C206S000700, C420S900000
Reexamination Certificate
active
06626323
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hydrogen storage units using hydrideable metal alloys to store hydrogen, and more particularly to a combined heat transfer management/compartmentalization system for use in such systems.
BACKGROUND OF THE INVENTION
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world's oil reserves are rapidly being depleted, the supply of hydrogen remains virtually unlimited. Hydrogen can be produced from coal, natural gas and other hydrocarbons, or formed by the electrolysis of water. Moreover hydrogen can be produced without the use of fossil fuels, such as by the electrolysis of water using nuclear or solar energy. Furthermore, hydrogen, although presently more expensive than petroleum, is a relatively low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of burning hydrogen is water.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of acceptable lightweight hydrogen storage medium. Conventionally, hydrogen has been stored in a pressure-resistant vessel under a high pressure or stored as a cryogenic liquid, being cooled to an extremely low temperature. Storage of hydrogen as a compressed gas involves the use of large and heavy vessels. In a steel vessel or tank of common design only about 1% of the total weight is comprised of hydrogen gas when it is stored in the tank at a typical pressure of 136 atmospheres. In order to obtain equivalent amounts of energy, a container of hydrogen gas weighs about thirty times the weight of a container of gasoline.
Additionally, transportation is very difficult, since the volume of the hydrogen stored in a vessel is limited, due to the low density of hydrogen. Furthermore, storing hydrogen as a liquid presents serious safety problems when used as a fuel for motor vehicles since hydrogen is extremely flammable. Liquid hydrogen must also be kept extremely cold, below −253 degree C., and is highly volatile if spilled. Moreover, liquid hydrogen is expensive to produce and the energy necessary for the liquefaction process is a major fraction of the energy that can be generated by burning the hydrogen.
Alternatively, certain metals and alloys have been known to permit reversible storage and release of hydrogen. In this regard, they have been considered as a superior hydrogen-storage material, due to their high hydrogen-storage efficiency. Storage of hydrogen as a solid hydride can provide a greater volumetric storage density than storage as a compressed gas or a liquid in pressure tanks. Also, hydrogen storage in a solid hydride presents fewer safety problems than those caused by hydrogen stored in containers as a gas or a liquid. Solid-phase metal or alloy system can store large amounts of hydrogen by absorbing hydrogen with a high density and by forming a metal hydride under a specific temperature/pressure or electrochemical conditions, and hydrogen can be released by changing these conditions. Metal hydride systems have the advantage of high-density hydrogen-storage for long periods of time, since they are formed by the insertion of hydrogen atoms to the crystal lattice of a metal. A desirable hydrogen storage material must have a high storage capacity relative to the weight of the material, a suitable desorption temperature/pressure, good kinetics, good reversibility, resistance to poisoning by contaminants including those present in the hydrogen gas and be of a relatively low cost. If the material fails to possess any one of these characteristics it will not be acceptable for wide scale commercial utilization.
Good reversibility is needed to enable the hydrogen storage material to be capable of repeated absorption-desorption cycles without significant loss of its hydrogen storage capabilities. Good kinetics are necessary to enable hydrogen to be absorbed or desorbed in a relatively short period of time. Resistance to contaminants to which the material may be subjected during manufacturing and utilization is required to prevent a degradation of acceptable performance.
Many metal alloys are recognized as having suitability for hydrogen storage in their atomic and crystalline structures as hydride materials. While this storage method holds promise to be ultimately convenient and safe; improvements in efficiency and safety are always welcome. This invention provides such improvement.
It is known that heat transfer capability can enhance or inhibit efficient exchange of hydrogen into and out of metal alloys useful in hydride storage systems. Such transfer is important since metal hydrides, being somewhat analogous to metal oxides, borides, and nitrides (“ceramics”) may be considered to be generally insulating materials. Therefore, moving heat within such systems or maintaining preferred temperature profiles across and through volumes of such storage materials becomes of interest in metal alloy-metal hydride hydrogen storage systems. As a general matter, release of hydrogen from the crystal structure of a metal or metal alloy to become a hydride requires input of some level of energy, normally heat. Placement of hydrogen within the crystal structure of a metal, metal alloy, or other storage system generally releases energy, normally heat, providing a highly exothermic reaction of hydriding.
In light of the heat input and heat dissipation needs of such systems, particularly in bulk, and in consideration of the insulating nature of the hydrided material, it is useful to provide means of heat transfer external to the storage material itself. Others have approached this in different ways, such as U.S. Pat. No. 6,015,041 which includes a heat-conductive reticulated open-celled “foam” to place within the hydrided or hydrideable material. The current invention provides for effective heat transfer throughout a hydrogen storage bed without the need for such foam.
Another recognized difficulty with hydride storage materials is that as the storage alloy is hydrided, it will generally expand and the particles of storage material will swell and, often crack. When hydrogen is released, generally on application heat, the storage material or hydrided material will shrink and some particles may collapse. The net effect of the cycle of repeated expansion and contraction of the storage material is comminution of the alloy or hydrided alloy particles into successively finer grains. While this process may be generally beneficial to the enhancement of overall surface area of the alloy or storage material surface area, it creates the possibility that the extremely fine particles may sift through the bulk material and settle toward the lower regions of their container and pack more tightly than is desirable. Forming such a high packing density region within a localized area may lead to localized excessive heating upon hydriding or hydrogen charging. The same highly packed localized high density region may also produce a great amount of strain on the vessel due to the densification and expansion (upon charging) of the hydrogen storage material. The densification and expansion of the hydrogen storage material provide the possibility of deformation or rupture of the container in which the hydrideable material is stored. While pressure relief devices may be useful in preventing such undesired occurrences as the container rupture due to the internal gas pressure of the vessel, pressure relief devices are unable to prevent deformation of the vessel resulting from densification and expansion of the hydrogen storage alloy. Others have approached the problem by dividing the container into simple compartments in a manner that prevents collection of too many fines in a particular compartment while allowing free flow of hydrogen gas throughout the container. The current invention provides for minimization of densification of particulate fines in h
Alper Daniel
Gorman David
Holland Arthur
Marchio Michael
Stetson Ned T.
Cronin Stephen K.
Energy Conversion Devices Inc.
Mau II Frederick W.
Merek Joseph C.
Schumaker David W.
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