FR2570689A1 - DEVICE AND METHOD FOR PRODUCING HYDROGEN - Google Patents

Abstract

HYDROGEN 10 PRODUCTION DEVICE FOR INFLATION OF HIGH ALTITUDE BALLOONS. IT INCLUDES AN ENCLOSURE 12 EQUIPPED WITH AN OUTPUT PASS 14 AND IN WHICH IS ARRANGED A SOLID UNIT MATRIX 16 OF ENDOTHERMICALLY DECOMPOSABLE METAL HYDRIDE HAVING A PREDETERMINED PERCENTAGE OF VACUUMS SO AS TO ALLOW A SADROGENTED RELEASE OF THE HYDROGEN. DECOMPOSITION, THE HYDRIDE MATRIX HAVING A SHAPE OF THE INTERIOR CONFIGURATION OF THE ENCLOSURE AND BEING SIZED TO PRACTICALLY FILL THE INTERIOR VOLUME OF THE ENCLOSURE, THE MATRIX PRESENTING A SERIES OF 20 HOLES DISTRIBUTED UNIFORMLY; A CHEMICAL SOURCE OF HEAT 24 PROVIDED INSIDE EACH HOLE TO PROVIDE EXOTHERMAL ENERGY TO DECOMPOSE HYDRIDE; A MEANS 28 FOR INITIATING THE REACTION FOR EACH CHEMICAL SOURCE OF HEAT; AND A MEANS 32 AVAILABLE ON THE OUTSIDE OF THE ENCLOSURE TO START THE MEANS FOR PRIMING THE REACTION.

Description

The present invention relates to production methods and devices

  of hydrogen in general and, more particularly, of processes and devices which can be

  applied to the high altitude inflation of film balloons

  fine cules launched by rockets.

  Inflators for film balloons

  fine cule launched by rockets at high altitudes of

  on the order of 20,000-30,000 meters, for example, must meet

  make a number of stringent conditions. Because of the space and weight limitations in the rocket, it is desirable that the inflation devices have a high volumetric capacity in a small volume

  total and be light. We must be able to store them safely.

  rity for long periods of time, and they must be able to quickly release the inflation gas so that

  the filling time for a balloon is of the order of

  only minutes. In addition, because of the high alti-

  study at which inflation takes place and the fragile nature of the thin films from which the balloons are constructed, it is

  necessary to have the assurance that the device does not create

  cune vapor, which could be at the origin, at the temperatures encountered at high altitude, of the formation

  ice that can cut the film, or chemicals

  mites likely to attack the film or form

  unwanted thermal coatings.

  -2 We prefer to use hydrogen instead of helium as an inflation gas in such applications, because it gives the highest specific lift of all possible gases that could be used for inflation (its lift is 7% higher than that of helium, for example). 450 g of hydrogen displaces approximately 6 kg of air, while 450 g of helium displaces only 3 kg of air. However, the use of

  hydrogen inflation raises problems, mainly related to

  security. Hydrogen can be stored either in gaseous or liquid form, or produced in a chemical system. A major drawback of gas storage systems is the need to use very high pressures and very heavy containers to contain the gas because of its pressure. There are obviously safety concerns which are inherent in the use of containers subjected to high pressure. Liquid cryogenic storage systems eliminate the need for high pressure storage, but their service life is limited due to heat loss. In addition, cryogenic systems raise safety concerns related to exposure to supercooled materials and the risk of hydrogen escape due to damage or

installation faults.

  Chemical systems are known for the production of

  tion of hydrogen which use compounds, such as hydrides, releasing hydrogen by chemical reaction or thermal decomposition. Such systems avoid most of the safety problems associated with compressed gas and cryogenic storage systems, and have even been the object of

  proposals for inflating balloons and the like

  bent as tags. However, known systems of this type do not satisfy the criteria relating to the smallness of the total volume, the lightness, and the rapid production of gas which is required from the inflating devices at high altitude of the large load-bearing balloons. . launched by rockets. It is desirable to have devices and methods for producing hydride-based hydrogen as an inflation system for such purposes, and this is the object of the present invention. The present invention provides a device and method for producing hydrogen which are particularly well suited for inflating balloons and the like at high altitude. The present invention is based on the use of metal hydrides which can decompose thermally.

  as a medium for safely storing hydro-

  gas gene, and on the use of chemical reagents that are inert, safe, and have a long lifespan as a heat source released quickly to decompose

  metallic hydrides in order to dissociate hydrogen therefrom.

  Briefly, a hydrogen production system according to the present invention comprises an enclosure containing

  a solid, unitary, decomposed metal hydride matrix

  thermally sand, comprising a predetermined percentage of voids so as to allow controlled release of hydrogen gas during decomposition. The matrix

  of hydride is shaped in such a way as to follow the internal form

  of the enclosure and practically filling the interior volume. The hydride matrix further comprises a series of holes distributed uniformly, each hole receiving a

  chemical source of heat in order to provide exo-

  thermal required for dissociation of hydrogen in the hydride matrix and a means of initiating the reaction for the heat source. A means for activating the means for initiating the reaction is disposed in the outer surface of the enclosure, and the latter comprises a passage for

  outlet for the evacuation of the released gaseous hydrogen.

  Preferably, the enclosure is spherical, because this shape allows the maximum storage volume in the space the

  lower, hence the minimization of the total volume of the available

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  and is the best form in terms of resistance.

  mechanical pressure for a pressurized structure, which minimizes the thickness and weight of the walls

  the enclosure. The metal hydride matrix is preferably

  that of magnesium hydride, which can be catalyzed by the addition of 5 to 10% by weight of nickel. The chemical source of

  heat preferably includes chemical compounds

  metallic or other exothermic chemical compounds, because they provide the greatest heat for the minimum weight and volume and can be used in a manner

  reliable. The heat source can be sheathed with a ceramic

  mique, for example, by being included in tubes inserted in the holes of the hydride matrix in order to avoid a reaction between the released hydrogen and the metals of the heat source. Recommended heat sources include titanium diboride and mixtures of beryllium and Mg (C104) 2.

  The following description refers to the figure

  attached which represents a sectional view of a generator

  hydrogen gas according to the present invention.

  The present invention is particularly suitable for a hydrogen production device for inflating

  balloons launched by rockets at high altitude, and will be de-

  written in this context. However, as will be noted,

  its field of use is wider and the description

  which follows will simply correspond to a type of application.

  As previously indicated, a device

  inflation with a balloon launched in high altitude

  of from a rocket must have as characteristics

  main a large volumetric capacity and a small vo-

  lume total, low weight, be safe, have a long life and allow rapid release of gases so as to obtain a filling time of the balloon of the order of two to three minutes, for example. Regarding the

  volume and weight, volume is usually the pa-

  reduces the most demanding, although volume and weight are also important. In addition, it is important that hydrogen

  gaseous product is free of water vapor and agents

  taminants, which could damage the balloon. The giant

  hydrogen gas generator of the present invention, comprising a decomposable metal hydride storage medium

  thermally and a chemical source having thermal energy

  high specific mique to provide the required heat

  for the dissociation of hydrogen, satisfies the conditions

  previous statements in an admirable and present manner

  other important features and advantages that appear

  will be seen in the following description.

  As shown in the figure, a hydro generator

  gene 10 according to the present invention comprises a container or enclosure 12 with a thin wall, preferably of spherical shape

  and can be made of stainless steel, for example.

  A spherical shape is recommended because it allows the volu-

  maximum storage space in the minimum space, and is the best configuration to use for a pressure vessel. A gas outlet port 14, for example tubular, is formed in the wall of the container 12 and is

  intended to be connected to a filling tube (not shown)

  wise balloon. Inside the container 12 is arranged a matrix 16 of solid unitary metal hydride (which

  we will describe below) comprising a spherical ball so-

  metal hydride liquid having dimensions such

  that it substantially fills the interior volume of the container

  pient. To allow the establishment of the hydride matrix in the container, the latter may consist, as is well known, of two hemispherical sections which are joined around the matrix. The hydride matrix can also have several holes 20 which can pass completely through it. Inside each hole we have

  arranged a heat source 24 electric start-

  ment and having a high specific thermal energy - 6 - (the source will be described more fully below). The heat sources 24 can be coated with an inert material

  hydrogen, such as ceramic or other suitable material

  required, so as to avoid any reaction between the hydrogen gas released by the hydride matrix and the materials of the heat sources, for example by enclosing the sources in cylindrical ceramic tubes 26 mounted inside holes 20. An electric igniter 28 comprising a conventional electric primer, for example,

  can be provided for each heat source and be

  connected by an electric wire 30 to an electric starting device 32, consisting, for example, of a battery and

  a switch (not shown). If necessary, a

  thermal insulation 34 may surround the outer surface

  container 12, although it can be dispensed with because the heat losses during the dissociation of the hydrogen will be less than about 1% of the heat energy

emitted by the heat source.

  In general, hydride storage media

  are characterized by a large volu-

  storage metric versus hydrogen storage

  gaseous or liquid. However, most metal hydrides-

  The liquids contain relatively low percentages of hydrogen per unit weight of hydride. Consequently, the choice of the particular hydride constituting the matrix 16

  must be done judiciously to avoid the penalties

  the weight we would otherwise have to suffer from.

  The following table 1 indicates the percentage by weight of hydrogen and the volumetric storage capacity of several different metal hydrides compared to the storage of compressed gaseous hydrogen, with the use of a pressure vessel made of coiled composite filament, (for example in filament of material called Kevlar) fitted with an aluminum coating, allowing hydrogen to be stored

pressures of the order of 50 MPa.

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TABLE 1

  COMPARISON OF HYDROGEN STORAGE MEDIA

  Medium Weight of hydrogen Capacity in% * storage H2 g / ml MgH2 7.6 0.132 TiH2 4.0 0.187

VH2 3.8 0.234

  FeTiH2 1.9 0.123 7TiFe 07Mn0.2Hl, 91.72 0.09 LaNi5H6.7 1.5 0.126

LH2 100 0.07

  H2 gas at MPa, 298 K 100 0.04 MPa, 298 K 100 0.008 * The weight of the container or the heat source is not

included.

  Among the metal hydrides mentioned above, magnesium hydride (MgH2) and vanadium hydride (VH2) are advantageous from the point of view of minimum weight and volumetric storage capacity. However, the choice of a particular optimum hydride depends not only on its weight and volume, but also on the relationship between its physical and thermal characteristics. The most important physical properties of a metal hydride for a light system, of small external volume, with a high volumetric storage capacity are its dissociation pressure as a function of temperature and its pressure in

  function of the composition isotherm. This last pro-

  priety determines the rate of dissociation of hydrogen

depending on the temperature.

  The desirable characteristic of the pressure as a function of the hydride temperature must be such that

  pressures are very low at storage temperatures

  kage, and only moderate at its dissociation temperature of hydrogen. As the inflation of a balloon involves only one dissociation reaction, instead of a cyclic operation as is the case with other known applications using hydrides, it is desirable to

  the safety plan of using a hydride having a tem-

  relatively high dissociation temperature.

  Magnesium hydride is the recommended hydride because it has the advantage of a minimum weight, very low pressures at storage temperatures, and only moderate pressure, (about 0.2 MPa, for example) at of

  temperatures of the order of 350 C, at which the decomposition

  tion is quite fast. At altitudes of about 21,000 meters, a pressure of 0.2 MPa is high enough to

  give a good gas flow in the balloon. Hydride of ma-

  gnesium should also be preferred over vanadium hydride, as the latter decomposes quickly at a rather low temperature, which could cause problems

of security.

  The use of magnesium hydride for consti-

  killing the metal hydride matrix 16 of the hydrogen generator 10 makes it possible to obtain a hydrogen storage system having a volume of only 40% of that of a

  compressed gas stored at a pressure of 50 MPa, and only

  about 70% of that of hydrogen stored in liquid state

  of. At normal ambient storage temperatures, magnesium hydride does not release any hydrogen. Even at

  much higher temperatures, for example in an in-

  fire, its hydrogen generation pressure is quite low (around 0.2 MPa at 350 C). Therefore, it avoids the inherent security issues that are

  associated with the storage of compressed gases and authorizes the use

  sation of a fairly light container, such as a stainless steel tank having a wall of 0.8 min. In addition, magnesium hydride has a fairly long storage life, of the order of several years. As indicated above, the hydride matrix 16 is preferably a solid unitary body having a predetermined percentage of

  voids and channels so as to control the speed of li-

  beration of dissociated hydrogen. We can form the matrix

  by repeatedly submitting a solid sphere of magnesium

  sium to heat and hydrogen gas until

  that magnesium is transformed into magnesium hydride

  sium and obtaining the desired volume of voids. Preferably,

  the void volume is around 20-25%. This cons-

  truction allows better control of the hydrogen release characteristic of the hydride matrix than in

  the case where the matrix is, for example, granular. Preferably

  magnesium hydride is catalyzed by the addition

about 5-10% by weight of nickel.

  In order to rapidly dissociate the hydrogen stored in the magnesium hydride matrix, there must be

  apply external heat to bring the time

  hydride temperature at its decomposition temperature, namely approximately 340 C. Per 450 g of hydrogen released by the matrix, it is necessary to provide the latter with an external heat of the order of 37,200 kJ / kg of hydrogen product (approximately 2580 kJ / kg MgH2). The heat source to provide

  this external heat preferably has a weight and a vo-

  minimum light, which requires a source having a high specific thermal energy, and which can be implemented in a reliable manner. A chemical source of heat

  work electrically, comprising intermetallic compounds

  ques or other chemical reagents of the thermite type can be used for this purpose. For example, the reaction of beryllium and Mg (ClO) 2 releases 15600 kJ / kg and more than 37 x 106

  -kJ per cubic meter. The volume percentage of these reactions

  tifs in relation to the total volume of the container would only be

- 10 -

  around 13%. Another advantage of using intermetallic compounds as a heat source is that they do not produce gases when they react, which should be evacuated and could cause unwelcome contaminants. As indicated above, depending on the particular reagents used, it may be necessary to sheath the reagents from the heat source, for example by placing them in a ceramic tube, so as to isolate them from the hydrogen. released by the hydride matrix. Table 2 below gives the characteristics of certain intermetallic compounds which can be used

  to constitute a heat source.

TABLE 2

  CHARACTERISTICS OF INTERMETALLIC REAGENTS

  * Heat Heat Temperature Temperature Expansion body average ignition temperature in that of in air reaction reaction reaction reaction CC kJ / kg 106kJ / m3 Li, B 4780 5.9 200 2500 Ti, B2 5120 12.5 550 3000 Ti, C 3000 8.5 600 2050 Be, C2 7310 15.5 1200 2740 * inert gas ** Theoretical Titanium diboride, for example, constitutes a

  good choice as a heat source. It presents a cha-

  their relatively high reaction temperature and a relatively high ignition temperature, above 540 C in air, desirable value to avoid premature ignition

  in a hot environment, such as a fire, but it is

- 11 -

  able to start ignition in a fraction of a second

  using the filament of an electrically heated lamp.

  The weight and volume of a titanium diboride heat source as a percentage of the weight and volume of the magnesium hydride matrix are of the order of 36% and 28%, respectively. Table 3 below gives the dimensions and the weight of a magnesium hydride / diboride generator.

  titanium capable of producing 4.5 kg of hydrogen.

TABLE 3

  DIMENSIONS AND WEIGHT OF THE GENERATOR TO PRODUCE

4.5 KG OF HYDROGEN.

  Weight MgH2 59.4 kg Titanium diboride and coating 33.7 kg Enclosure 4.5 kg Priming battery and various accessories 3.6 kg Total weight 101.2 kg Dimensions Sphere 45.7 cm outside diameter Stored hydrogen in the matrix of magnesium hydride can be released quickly in the desired time, namely of the order of 2 to 3 minutes, insofar as the temperature of the matrix can be maintained at a value of approximately 350 C. For the generator in table 3, the heat

  which must be transferred to the matrix and the time of supply

  required ture are indicated in the following table 4:

- 12 -

TABLE 4

  HEAT NECESSARY TO PRODUCE 4.5 kg of HYDROGEN Increase of 15 C to 350 C of the temperature of the hydrogen generator 35.600 kJ (estimated heat capacity = 1 J / kg- C) Endothermic energy for dissociation 168.800 kJ Total energy 204.400 kJ Heat transfer rate (2 minutes supply) 6.12.106 kJ / h As shown in Table 4, to give 4.5 kg of hydrogen, the heat source must produce a net energy of 204.400 kJ, and provide this energy at a rate of 6.12.106 kJ / hour. To satisfy these conditions of energy supply, it is desirable that the tubes 24 of the heat source are distributed uniformly in the hydride matrix. You can easily determine the number of tubes, their diameter, and their spacing to obtain the heat transfer surface to meet the

energy supply rate.

  - In addition, it is necessary to have the assurance that the surface of the circulation channels is sufficient for the hydrogen produced to be released by the generator. Because of the logarithmic relationship between the pressure of a gas and

  of temperature, the rise in temperature inside

  of the matrix will be low for large increases

  gas pressure, and the effect of establishing

  the pressure on the heat transfer will be

  nimal. To maintain a maximum pressure of hydrogen of the order of 34.5 kPa or less, for example, one can control the rate at which hydrogen gas is dissociated from the matrix by adjusting the volume of voids in the matrix by

- 13 -

  relative to the dimensions of the outlet opening 14 of the container

  pient. It is desirable that the volume of voids in the ma-

  be around 20-25%, because as this

  lume increases, the volume of the generator required to supply

  The required volume of gas increases and the thermal conductivity of the metal matrix decreases. 20-25% void volume will not reduce conductivity

  thermal value of the matrix of appreciable value at temperature

  dissociation of magnesium hydride.

  The use of intermetallic compounds as

  heat source for the hydride matrix is a characteristic

  particularly important and advantageous

  present invention. Intermetallic compounds are inert

  are safe and have a relatively long shelf life

  long. In addition, the arrangement of intermetallic compounds

  that inside ceramic tubes has the effect of

  ler the reaction products and ensure that the hydrogen released by the hydride matrix is clean and free of

  contamination agents that could damage the film

  fine cule from which the balloon is made. Regarding the se-

  curiosity, you just have to be sure that it doesn't

  will not produce premature ignition of the heat source.

  Consequently, the electric starting device 32 must have a low probability of false ignition, which

  which is fairly easy to obtain with conventional techniques

  ques. As can be appreciated from the above, the present invention provides a generator

  particularly simple and extremely advantageous hydrogen

  which can be used as a source of hydrogen for

  inflation of a balloon launched from a high-altitude rocket

  titude. The hydrogen generators of the present invention do not suffer from the drawbacks of compressed gas or liquid hydrogen storage systems, are light and have a high volumetric capacity, and can have a

- 14 -

  high rate of hydrogen production. Other apps

  cations of the hydrogen generator of the present invention

  relates to its use in a source delivering points

  your high power for short periods and its use in conjunction with transforming devices

  energy such as magneto-hydrodynamic generators

  open cycle, fuel cells, and machinery

  nes of dynamic energy conversion operating according to

  the Brayton cycle or the Stirling cycle, for example.

- 15 -

Claims (22)

  1. Hydrogen production device (10) ca   characterized in that it comprises an enclosure (12) provided with a   outlet passage (14) and in which a ma-   Solid unit trice (16) of a decomposed metallic hydride   endothermic sand with a predetermined percentage-   mined with voids to allow controlled release   lée of hydrogen during its decomposition, the matrix   hydride having a shape marrying the internal configuration   of the enclosure and being sized to fill pra-   the interior volume of the enclosure, the matrix pre-   feeling a series of holes (20) distributed uniformly; a chemical heat source (24) disposed inside each hole to provide exothermic energy to   decompose hydride; a means (28) for initiating the reaction   tion for each chemical source of heat; and means (32) disposed on the outside of the enclosure for placing   works the means of initiating the reaction.   2. Device according to claim 1, charac-   that the metal hydride is magnesium hydride sium.   3. Device according to claim 2, character-   dried in that magnesium hydride is catalyzed by addi- 5-10% by weight of nickel.   4. Device according to claim 2, character-   se in that the predetermined percentage of voids is   around 20-25% of the volume of the matrix.   5. Device according to claim 1, character-   dried in that the chemical source of heat (24) is   containing one or more intermetallic compounds.   6. Device according to claim 5, charac-   dried in that the chemical heat source (24) is coated   of a material which is inert towards hydrogen.   7. Device according to claim 6, charac-   dried in that chemical sources of heat are arranged - 16 -   inside ceramic tubes (26) which are received in the holes (20).   8. Device according to claim 1, character-   dried in that the chemical heat source (24) comprises titanium diboride.   9. Device according to claim 1, character-   dried in that the chemical heat source (24) comprises beryllium and Mg (C104) 2.   10. Device according to claim 1, character-   risé in that the enclosure (12) is spherical.   11. Device according to claim 1, character-   laughed in that the means (28) for initiating the reaction and the   start-up means (32) operate electrically.   12. Device according to claim 1, character-   rised in that it is dimensioned so as to be arranged inside a rocket and intended to carry out inflation at   high altitude of a balloon launched by the rocket.   13. Device according to claim 1, character-   risé in that the enclosure (12) comprises a thermal insulator (34) on its outer surface.   14. Method for producing hydrogen, characterized in that it consists in: - placing inside a chamber (12) comprising an outlet passage (14) a solid unitary matrix (16) of a hydride metallic which can decompose endothermically and having a predetermined percentage of voids so as to allow a controlled release of hydrogen during its decomposition, the matrix having several holes (20) distributed uniformly, the matrix having a shape matching   the interior configuration of the enclosure and being dimen-   sioned so as to practically fill this enclosure; - placing inside each hole a chemical heat source (24) having a high specific energy; - initiate the reaction of the chemical source of heat in order to produce heat and thermally decompose - 17 -   hydride to release hydrogen; and   - collect hydrogen released at the outlet passage (14).   15. Method according to claim 14, characterized   in that the hydride is magnesium hydride.   16. The method of claim 15, characterized in that it further comprises the catalysis of hydride of   magnesium by addition of 5-10% by weight of nickel.   17. Method according to claim 14, characterized   in that the voids represent 20-25% by volume of the ma- hydride.   18. Method according to claim 14, characterized in that the chemical heat source (24) comprises one or   several intermetallic compounds.   19. Method according to claim 18, characterized   in that it further comprises the coating of the compounds   termetallic with a material which is inert towards hydrogen. 20. Method according to claim 19, characterized   in that the material consists of a ceramic.   21. Method according to claim 14, characterized in that the chemical heat source (24) consists of titanium diboride.   22. Method according to claim 14, characterized in that the chemical heat source (24) is constituted beryllium and Mg (C104) 2.