JPS61111901A - Hydrogen storage system by metallic hydride proper for expanding balloon - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Background of the Invention The present invention relates to a hydrogen generation method and device, and more specifically, a method applicable to the purpose of inflating a thin film balloon launched from a rocket at a high altitude. and regarding equipment.

Apparatus for inflating thin film balloons launched from rockets at altitudes on the order of 70,000 to ioooooo feet, for example, must meet several very demanding requirements. Due to the volume and weight limitations of rockets, it is desirable for such an inflatable device to have a small overall volume, exhibit a large volumetric storage capacity, and be lightweight. They must be able to be safely stored for long periods of time and must be capable of releasing inflation gas rapidly so that balloon filling times are only a few minutes. Furthermore, given that the balloon is inflated at a high altitude and the thin membrane that makes up the balloon is easily torn,
It is also necessary to avoid the formation of water vapor, which can form ice at high temperatures (which tends to cut the membrane), or chemicals that can lead to erosion of the membrane or the formation of unwanted thermal films. .

Hydrogen is preferred over helium as the inflation gas for such applications. This is because of all the gases that can be used for inflation, hydrogen provides the greatest residual lifting force (eg, 7% more than helium). Also, 1 bond of hydrogen displaces approximately 13 bonds of air, whereas 1 bond of helium displaces only 7 bonds of air. However, hydrogen gas expansion devices have problems, primarily with respect to safety. Hydrogen can be stored as a gas or liquid, or it can be generated in a chemical device. A major drawback of gas storage devices is that they require extremely high pressures and extremely durable storage containers to meet such high pressure conditions. Of course, there are safety issues associated with the use of high pressure vessels. Although cryogenic liquid storage devices eliminate the need for high pressure storage, heat leakage limits shelf life. Additionally, cryogenic equipment has safety issues associated with exposure to supercooled materials, and there is also the potential for hydrogen leakage due to equipment damage or defects.

As chemical devices for generating hydrogen, those using compounds (eg, hydrides) that liberate hydrogen by chemical reaction or thermal decomposition are known. Such a device would avoid many of the safety issues associated with compressed gas storage devices and cryogenic storage devices, and is similar to devices previously proposed for inflating balloons used as location markers. It's here. However, in known devices of this type, the conditions of small overall volume, light weight and rapid gas release are required for the inflation device for inflating at high altitudes a heavy balloon launched from a rocket. is not satisfied. It is therefore desirable to provide a hydride-based hydrogen generation device and method to be used for the above-mentioned applications, and the present invention aims to achieve this objective.

SUMMARY OF THE INVENTION According to the present invention, a hydrogen generation device and method are provided that are particularly well suited for the purpose of inflating balloons and the like at high altitudes. The present invention uses pyrolyzable metal hydrides as a medium to safely store hydrogen gas and also as a long-life inert and rapid heat source to decompose the metal hydride and dissociate hydrogen from it. It is based on the principle of using safe chemical reactants.

Briefly stated, the hydrogen generator of the present invention consists of a solid monolithic member of a pyrolyzable metal hydride having a predetermined percentage of voids to enable controlled release of hydrogen gas during decomposition. It consists of a storage container with . The metal hydride matrix has a shape that matches the internal contour of the storage container and dimensions that substantially fill the internal volume of the storage container. The interior of the metal hydride matrix is also provided with a plurality of evenly distributed pores. Each such hole houses a chemical heat source that provides the exothermic energy necessary for hydrogen dissociation in the metal hydride matrix and a reaction initiation means for such chemical heat source. An actuation means for actuating the reaction initiation means is disposed on the outer surface of the storage container, and the storage container is also provided with an outlet for free hydrogen gas.

Preferably, the storage container described above is spherical. Because spheres can minimize the overall volume of the device by providing maximum storage volume in minimum space,
Also, from the viewpoint of strength, the shape is the best for the pressure vessel, so that the wall thickness and weight ε of the storage vessel can be minimized. Preferably, the metal hydride for the base material is magnesium hydride, and
~10 (ffifa)% of nickel can also be added as a catalyst. The chemical heat source preferably comprises an intermetallic compound or other exothermic chemical reactant because it produces the maximum amount of heat with the minimum weight and volume and can operate reliably. The chemical heat source can also be coated with ceramic (eg, by encapsulating it in a tube inserted into a hole in the matrix) to prevent reaction of the released hydrogen with the heat source material. Suitable chemical heat sources include titanium diboride and mixtures of beryllium and MO (CI 04 >2).

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention utilizes a balloon launched from a rocket at a high altitude.
It is particularly well suited for hydrogen generators for boiling, and the following description will also be made in connection therewith. It goes without saying, however, that the present invention has a much broader range of utility, and that the above objectives are merely illustrative of the uses of the present invention.

As mentioned above, the main requirements for a hydrogen generator for inflating balloons launched from rockets at high altitudes are: large volumetric storage capacity, small overall volume, and light weight.
Advantages include safety, long shelf life, and rapid gas release (e.g., giving a balloon fill time on the order of 2-3 minutes). Although both volume and volume are extremely important, volume generally constitutes the most stringent requirement.

Furthermore, it is important that the hydrogen gas generated does not contain water vapor or contaminants that could cause damage to the balloon. The hydrogen generator of the present invention, consisting of a pyrolyzable metal hydride storage medium and a chemical heat source with high specific thermal energy that supplies the heat required for hydrogen dissociation, certainly meets these requirements. However, it also has important features and advantages of its own, which will become clear from the description below.

As shown in the attached drawings, hydrogen generator 1 of the present invention
0 includes a thin-walled storage container 12.

Such storage container 12 is preferably a balloon, which can be manufactured from stainless steel, for example. Balloons are preferred because they provide maximum storage volume in minimum space and because they are the best shape for use as pressure vessels. A gas outlet 14, for example tubular, is provided in the wall of the storage container 12, which can be connected to a balloon filling tube (not shown). Disposed within the interior of the storage container 12 is a solid unitary member 16 (as described in more detail below) comprising solid spheres of metal hydride having dimensions such that the interior volume of the storage container 12 is substantially filled. ing. Such base material 1
6 can be placed inside the storage container 12, the storage container 12 can be constructed from two hemispheres that can be combined after surrounding the base material 16, as is known in the art.

Furthermore, although a plurality of holes 20 are provided inside the base material 16, these holes may penetrate through the base material 16. Inside each hole is an electrically operated high specific heat energy heat source 2 (also detailed below).
4 is placed.

The heat source 24 can also be coated with a material inert to hydrogen (eg, ceramic or other suitable material) to prevent reaction between the hydrogen gas liberated from the base material 16 and the heat source material. To do this, for example, the heat source 24 may be enclosed within a cylindrical ceramic tube 26 placed inside the hole 20.

Each of the heat sources 24 is equipped with an electric igniter 28, for example consisting of a conventional electric ignition tube, and an electric actuator 3 consisting of, for example, a suppressor and a switch (not shown).
2 via an electrical lead wire 30. If desired, a layer of thermal insulation material 34 may be placed surrounding the exterior surface of the container 12.

However, since the heat loss during hydrogen dissociation is less than about 1% of the heat generated from heat source 24, layer of insulation 34 may be omitted.

In general, metal hydride storage media are characterized by a larger volumetric storage capacity than when storing hydrogen gas or liquid hydrogen. However, most metal hydrides have relatively low hydrogen content per unit weight. Therefore, the metal hydride for the matrix 16 needs to be carefully selected to avoid the disadvantages associated with m6. In Table 1 below, the hydrogen loading percentage and volumetric storage capacity for several metal hydrides are shown. Also, for comparison, 5
A composite filament with an aluminum liner [e.g. Kevlar (K
Values for compressed hydrogen gas storage using a one-turn filament pressure vessel are also shown.

Among the metal hydrides shown in the table, magnesium hydride (MU H2) and vanadium hydride (VH2) are preferred in terms of smallest weight and large volumetric storage capacity.
is promising. However, the selection of the optimal metal hydride depends not only on the amount and volumetric properties, but also on the relationship between physical parameters and thermal requirements. The most important physical properties for metal hydrides for devices with 1 m light weight, small external volume, and large volume storage capacity are the dissociation pressure and the isomixture of pressure versus composition as a function of temperature. The latter serves to determine the rate of hydrogen dissociation as a function of temperature.

The pressure/temperature characteristics of such a metal hydride are desirably such that it exhibits an extremely low pressure at the storage temperature and only a suitably low pressure even at the hydrogen dissociation temperature. In the case of balloon expansion, only a single dissociation reaction is involved, unlike in the case of cyclic operations as seen in other known applications of hydrides, so that metal hydrides with relatively high dissociation temperatures are used. It is desirable to use it from a safety point of view.

has the lowest weight and exhibits extremely low pressure at storage temperatures;
The preferred metal hydride is magnesium hydride, since it exhibits only moderately low pressures (e.g., about 2 atmospheres) at temperatures as high as 660"F, where extremely rapid decomposition occurs. At altitudes of 2 atmospheres, a pressure of 2 atmospheres is sufficient to obtain a good rate of gas inflow into the balloon. Vanadium hydride decomposes rapidly at relatively low humidity, creating safety issues. Magnesium hydride is preferred over vanadium hydride due to the fact that

When magnesium hydride is used as the metal hydride matrix 16 of the hydrogen generator 10, it has a volume corresponding to only about 40% of that for compressed hydrogen gas storage at 500 atmospheres, and for liquid hydrogen storage. A hydrogen storage device is obtained having a volume corresponding to approximately 70% of the total. Normal savings! At temperature, magnesium hydride does not release any hydrogen. Even at fairly high temperatures, such as during a fire, its hydrogen generation pressure is relatively low (on the order of 2 atmospheres at 660″F). Therefore, the safety issues associated with compressed hydrogen gas storage are avoided; It also allows the use of relatively lightweight storage containers, such as 1/32 inch thick stainless steel tanks. Additionally, magnesium hydride has a relatively good shelf life of several years. The metal hydride matrix 16 preferably comprises a solid body having a predetermined proportion of voids and passageways to allow control of the rate of release of dissociated hydrogen, as described above. can be formed by repeatedly exposing solid spheres of magnesium to heat and hydrogen gas and continuing the operation until the magnesium is converted to magnesium hydride and the desired porosity is obtained. is preferably about 20-25%. When such a structure is used, the hydrogen gas release properties are improved even better than when the matrix is, for example, granular.
It becomes possible to Furthermore, it is preferable to add about 5 to 10 (Im)% of nickel to the magnesium hydride as a catalyst.

To rapidly dissociate the hydrogen stored in the magnesium hydride matrix, external heating must raise the temperature of the matrix to a decomposition temperature of approximately 650″F. When releasing hydrogen, approximately 160,008 TU per hydrogen bond (M (approximately 1 per 1,821 bond)
1008 TU) of heat must be supplied to the base material from the outside. It is desirable that a heat source for externally supplying such heat have a minimum mass and volume (ie, a high specific heat energy heat source) and also be able to operate reliably. For such purposes, electrically operated chemical heat sources consisting of intermetallic compounds or their thermite type chemical reactants can be used. For example, beryllium and M(1(CI Os )
The reaction with 2 generates 7200 BTU/lb of heat, which is more than 1,000,000 BTU/ft3.

The volume percentage of these reactants relative to the total volume of the storage container is only about 13%. Another advantage of using intermetallic compounds as heat sources is that they do not evolve gases during reaction, thus eliminating the need for degassing and the possibility of the formation of undesirable contaminants. As previously mentioned, depending on the reactants used, it may be necessary to coat the heat source material (e.g. by placing it in a ceramic tube) to isolate it from the hydrogen released from the metal hydride matrix. There is. Table 2 below shows the properties of other reactive intermetallic compounds that can be used as heat sources.

Table 2 88 Theoretical Values For example, titanium diboride is suitable as a heat source. It produces a relatively large heat of reaction and has a relatively high ignition temperature of over 1.000"F in air. The latter property avoids premature ignition in high temperature environments (e.g. fire). While this is desirable, an electric heating filament can initiate ignition of titanium diboride in a fraction of a second.

The ff1ffl and volume of the titanium diboride heat source are about 36% and 28%, respectively, based on the weight and volume of the magnesium hydride base material.

In Table 3 below, the dimensions and II of a magnesium hydride/titanium diboride device capable of generating 10 bonds of hydrogen are shown.

Table 3 Hydrogen stored in magnesium hydride can be rapidly released within a desired time period of about 2-3 minutes if the temperature of the matrix is maintained at a value on the order of 660''F. 4th of
The table shows the heat that must be transferred to the base material in the apparatus of Table 3 and the required transfer time.

Table 4 As shown in Table 4, to generate 10 bonds of hydrogen, the heat source must generate 193,750 BTU of net energy and transfer such energy at a rate of 5.8 x 106 BTU/hr. Must. In order to satisfy such energy transfer conditions, it is desirable that the heat source be uniformly distributed within the metal hydride matrix. The number of heat sources, the diameter of the heat sources, and the spacing between the heat sources can be easily determined to provide sufficient heat transfer area to satisfy the energy transfer requirements.

Furthermore, it is also necessary to ensure a sufficient flow path area so that the generated hydrogen can be discharged from the device.

Since gas pressure changes logarithmically with respect to temperature, even if the gas pressure increases significantly, the temperature inside the base material increases only slightly, and therefore the influence of increased pressure on heat transfer is minute.

In order to maintain the maximum hydrogen pressure below, for example, about 5 psia, the rate at which hydrogen gas dissociates from the matrix can be controlled by adjusting the porosity of the matrix relative to the dimensions of the outlet 14 of the containment vessel. good. Considering that as the porosity increases, the volume of the equipment required to generate the required amount of gas increases and the thermal conductivity of the base material decreases, the porosity of the base material is approximately 20 to 25%. It is preferable that 20-2
If a porosity of about 5% is used, the thermal conductivity of the base material will not drop significantly at a solution of magnesium hydride of 11 degrees.

The use of an intermetallic compound as a heat source for the metal hydride matrix constitutes a particularly notable and highly advantageous feature of the invention. Intermetallic compounds are inert and safe;
Moreover, it has a relatively long shelf life. Furthermore, by placing the intermetallic compound within a ceramic tube to isolate the reaction products, the hydrogen liberated from the metal hydride matrix does not contain contaminants that could damage the thin film materials that make up the balloon. kept in a clean condition. From a safety point of view, it is only necessary to prevent premature ignition of the heat source. Therefore, the electric actuator 32 must have a low probability of malfunction, which can be achieved relatively easily using conventional techniques.

As can be seen from the above description, the present invention inflates a balloon launched from a rocket at a high altitude. The present invention provides a particularly simple and extremely advantageous hydrogen generating device that can be used as a hydrogen source for.

The hydrogen generation device of the present invention overcomes the drawbacks of compressed hydrogen gas or liquid hydrogen storage devices, has light weight R and large volumetric storage capacity, and can generate hydrogen rapidly.

Other applications of the hydrogen generator of the present invention include use in power supplies that produce multiple j peaks of power over short periods of time. That is, open cycle MHD
(magnetohydrodynamic) generators, fuel cells, and playton (
Brayton) cycle and Sterling (3tirl)
It can be used in conjunction with an energy conversion device, such as a power conversion device operating on the basis of incl) cycles.

Although the preferred embodiments of the present invention have been described above, various changes may be made to the embodiments without departing from the principles and spirit of the present invention whose scope is defined by the claims. will be obvious to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS The single figure is a cross-sectional view of a hydrogen generation device according to the invention. In the figure, 10 is a hydrogen generator, 12 is a storage container, 14 is an outlet, 16 is a metal hydride base material, 20 is a hole, 24 is a heat source,
26 represents a ceramic tube, 28 an electric igniter, 30 an electric lead, 32 an electric actuator, and 34 a layer of insulation.

Claims (1)

[Claims] 1. Endothermically decomposable metallic hydrogen having (a) a storage container having an outlet, and (b) a predetermined ratio of voids to allow controlled release of hydrogen during decomposition. a solid monolithic matrix disposed within the storage container, having a shape that conforms to the internal contour of the storage container and dimensions that substantially fill the internal volume of the storage container; and (c) a chemical heat source disposed within each of said pores to provide exothermic energy to decompose said metal hydride; (d) A hydrogen generation device comprising reaction initiation means for each of the chemical heat sources, and (e) actuation means disposed outside the storage container for actuating the reaction initiation means. 2. The device according to claim 1, wherein the metal hydride comprises magnesium hydride. 3. Claim 2, wherein 5 to 10% (by weight) of nickel is added to the magnesium hydride as a catalyst.
Apparatus described in section. 4. The predetermined ratio of voids is 20 to 25 of the volume of the base material.
% of the device according to claim 2. 5. The apparatus of claim 1, wherein the chemical heat source comprises one or more metal compounds. 6. The apparatus according to claim 5, wherein the chemical heat source is coated with a material inert to hydrogen. 7. The apparatus of claim 6, wherein said chemical heat source is located inside a ceramic tube housed within said bore. 8. The apparatus of claim 1, wherein said chemical heat source comprises titanium diboride. 9. The apparatus of claim 1, wherein the chemical heat source comprises beryllium and Mg(ClO_4)_2. 10. The device according to claim 1, wherein the storage container is spherical. 11. The apparatus according to claim 1, wherein said reaction initiation means and said actuation means are electrically operated. 12. The device according to claim 1, wherein the hydrogen generator has a size that can be placed inside a rocket, and is applied for the purpose of inflating a balloon launched from the rocket at a high altitude. 13. The device of claim 1, wherein the storage container has a heat insulating material on its surface. 14. (a) providing a containment vessel with an outlet; (b) consisting of an endothermically decomposable metal hydride having a predetermined proportion of voids to permit controlled release of hydrogen during decomposition; a solid monolithic member having a plurality of evenly distributed holes therein, a solid monolithic matrix having a shape that conforms to the internal contour of the storage container and dimensions that substantially fill the storage container; , disposed inside the storage container, (c) supplying a chemical heat source with high specific thermal energy to the inside of each of the holes, and (d) heating the metal hydride by initiating a reaction of the chemical heat source. A method for generating hydrogen, comprising the steps of generating heat for decomposing and liberating hydrogen, and then (e) collecting the liberated hydrogen at the outlet. 15. The method of claim 14, wherein the metal hydride comprises magnesium hydride. 16. The method according to claim 15, comprising the step of adding 5 to 10% (by weight) of nickel to the magnesium hydride as a catalyst. 17. The method according to claim 14, wherein the voids occupy 20 to 25% of the volume of the base material. 18. The method of claim 14, wherein said chemical heat source comprises one or more intermetallic compounds. 19. The method according to claim 18, comprising the step of coating the intermetallic compound with a material inert to hydrogen. 20. The method of claim 19, wherein said material comprises a ceramic. 21. The method of claim 14, wherein said chemical heat source comprises titanium diboride. 22, the chemical heat source is beryllium and Ma(ClO_
4) The method of claim 14 consisting of_2.