Hydrogen supply method

A system for supplying hydrogen to an apparatus which utilizes hydrogen, contains a metal hydride hydrogen supply component and a microcavity hydrogen storage hydrogen supply component which in tandem supply hydrogen for the apparatus. The metal hydride hydrogen supply component includes a first storage tank filled with a composition which is capable of forming a metal hydride of such a nature that the hydride will release hydrogen when heated but will absorb hydrogen when cooled. This first storage tank is equipped with a heat exchanger for both adding heat to and extracting heat from the composition to regulate the absorption/deabsorption of hydrogen from the composition. The microcavity hydrogen storage hydrogen supply component includes a second tank containing the microcavity hydrogen supply. The microcavity hydrogen storage contains hydrogen held under high pressure within individual microcavities. The hydrogen is released from the microcavities by heating the cavities. This heating is accomplished by including within the tank for the microcavity hydrogen storage a heating element.

BACKGROUND OF THE INVENTION 
This invention pertains to a system for supplying hydrogen to a hydrogen 
utilizing apparatus utilizing a combination of a metal hydride hydrogen 
storage and microcavity hydrogen storage. 
Because from an environmental standpoint hydrogen can be cleanly used, 
because hydrogen has a large capacity for energy transference, and because 
there is a reversible supply of hydrogen in the form of water, the 
utilization of hydrogen as a fuel for many different systems is becoming 
incresingly important. Hydrogen can be used as a fuel in apparatuses which 
are powered by combustion engines wherein hydrogen is oxidized and the 
energy obtained in this oxidation process is used to power the engine with 
the only product of oxidation being water. Additionally hydrogen can be 
used as a fuel for electrical energy generation utilizing either the heat 
of combustion to drive conventional steam turbines or direct use of 
hydrogen within fuel cells. 
At all temperatures except cryogenic temperatures hydrogen exists as a gas. 
The storage of large supplies of hydrogen as a gas presently is done by 
compressing the hydrogen and storing in large tanks. However, because the 
hydrogen is under high pressure it is necessary that these tanks to very 
strong which in turn necessitates very thick walls and heavy tanks. When 
hydrogen is stored as a liquid at cryogenic temperatures, as with hydrogen 
as a gas, cryogenic liquid hydrogen must also be contained in strong, 
heavy tanks and additionally there is an energy penalty in the 
liquefaction process. Aside from the weight disadvantages of hydrogen 
storage in tanks both as a liquid and a gas, the storage tank must be 
designed and constructed of suitable materials to accommodate and control 
the permeability and reactivity of hydrogen with most metals. 
It has been proposed to store hydrogen chemically bound in a chemical 
carrier such as methylcyclohexane which is catalytically converted to 
toluene and hydrogen, the hydrogen being used as fuel and the toluene 
being recycled back to methylcyclohexane. Use of such a system requires 
two transporation networks, one for the delivery of the methylcyclohexane 
to a service station for dispensing to the consumer, the other for the 
return of the toluene to a reconversion plant to be hydrogenated into 
methylcyclohexane. This type of system is still in a semihypothetical 
state and much technology remains to be developed until each systems can 
hope to be functional. 
A system now being field tested for utilizing hydrogen as a fuel to propel 
an automobile involves the use of a metal hydride as the carrier for the 
hydrogen fuel. Basically this system involves having a storage tank filled 
with a metal that reversibly forms a metal hydride. In the presence of 
hydrogen and the withdrawal of heat, the metal absorbs the hydrogen 
forming a metal hydride. Upon the application of heat the hydride 
disassociates into the metal and hydrogen allowing the hydrogen to be 
utilized as fuel. The heat to disassociate the metal hydride is obtained 
from the hot exhaust gases from the engine. Currently two metal hydride 
systems are being studied for use in automobiles. One system is based upon 
a hydride of an iron titanium alloy and the second system is based upon 
hydrides of magnesium alloys. 
The disadvantage of a total metal hydride system is that the system is both 
heavy and expensive. The weight problem becomes critical in mobile 
applications such as automobiles, buses, etc., wherein transportation of 
the added weight reduces the fuel economy of the vehicle. In stationary 
system such as systems utilizing hydrogen in the generation of 
electricity, weight of the system is not the critical factor however, in 
these systems wherein large quantities of metal hydrides will be required 
the economics of the system become critical. 
An additional factor to be considered in mobile systems such as automobile 
usage of metal hydride systems is the refueling (i.e. regenerating the 
metal hydride) of the on board metal hydride vehicle storage tank. During 
refueling the vehicle storage tank would have to be coupled to a unit 
which withdrew heat from the storage tank allowing for the regeneration of 
the metal hydride. This would require at complex hookup of hydrogen supply 
line and cooling line. Compared to the typically five minute stop now 
necessary to obtain a supply of gasoline, the regeneration of the metal 
hydride could require a prolonged fuel stop. 
BRIEF SUMMARY OF THE INVENTION 
In view of the above it is evident that there is a need for new and 
improved systems which supply hydrogen to an apparatus utilizing hydrogen 
as a fuel. It is therefore a broad object of this invention to fulfill 
this need. It is a further object of this invention to provide a hydrogen 
supply system which is not as expensive as an exclusively metal hydride 
hydrogen system. Additionally it is an object of this invention to furnish 
a system which has a hydrogen capacity similar to that of liquid hydrogen 
yet does not involve the dangerous usage of large quantities of either 
liquid or gaseous hydrogen. Additional objects include a hydrogen supply 
system which will deliver hydrogen at greater than atmospheric pressure to 
the apparatus which will use the hydrogen yet does not require equilibrium 
storage pressures greater than approximately 50 or 60 atm. 
These and other objects are fulfilled by providing a hydrogen supply system 
which utilizes a metal hydride hydrogen supply component and a microcavity 
hydrogen storage hydrogen supply component both components supplying 
hydrogen to an apparatus using hydrogen and additionally the microcavity 
hydrogen storage hydrogen supply component supplying hydrogen to recharge 
the metal hydride hydrogen supply component and the system incorporates 
the metal hydride hydrogen supply component including a storage tank 
filled with a composition including a metal capable of forming a metal 
hydride and having a heat exchanger to regulate the temperature of the 
metal hydride to control absorption/deabsorption of hydrogen from the 
hydride and the microcavity hydrogen storage hydrogen supply component 
includes a storage tank containing a microcavity hydrogen storage and a 
heating element for heating the microcavity hydrogen storage to release 
hydrogen from the microcavity hydrogen storage and further having 
regulating valves within the system to regulate the flow of hydrogen from 
both the metal hydride hydrogen supply component and the microcavity 
hydrogen storage hydrogen supply component to the hydrogen utilizing 
apparatus and the flow of hydrogen from the microcavity hydrogen storage 
hydrogen supply component to the metal hydride hydrogen supply component.

The invention in this specification utilized certain operative concepts or 
principles as are set forth and defined in the appended claims forming a 
part of the specification. Those skilled in the art to which this 
invention pertains will realize that these concepts or principles can 
easily be applied to a number of differently appearing and differently 
described embodiments and for this reason the invention is not to be 
construed to be limited to the illustrated embodiments but is to be 
construed in light of the claims. 
DETAILED DESCRIPTION 
FIG. 1 shows a generalized embodiment of the invention wherein a hydrogen 
consuming apparatus 10 is supplied with hydrogen utilizing the hydrogen 
supply system of the invention. The apparatus 10 could be an energy 
generating apparatus such as a combustion engine or a fuel cell or it 
could also be a process plant which utilizes hydrogen as a chemical 
reactant. Typical process plants include those producing organic chemicals 
or fertilizers and steel mills which utilize hydrogen as a reducing agent. 
In any event hydrogen is supplied to the hydrogen consuming apparatus 10 by 
a supply system which has a microcavity hydrogen storage hydrogen supply 
component 12 and a metal hydride hydrogen storage hydrogen supply 
component 14. The metal hydride component 14 supplies hydrogen for short 
term hydrogen utilization needs such as peak loading or acceleration. The 
microcavity component 12 supplies an overall constant demand for hydrogen 
and is also used to regenerate or refuel the metal hydride component 14. 
To release hydrogen from both component 12 and component 14 these 
respective components are supplied with heat which causes both the 
microcavity hydrogen supply and the metal hydride hydrogen supply to 
release hydrogen. For energy generating apparatuses such as fuel cells or 
combustion engines the usual source of this heat is the waste heat given 
off by either the engine or the fuel cell. 
The control of the rate of discharge of hydrogen from both component 12 and 
14, as hereinafter discussed, is governed by the control of the rate of 
heating of the components 12 and 14. To achieve this the components 12 and 
14 are equipped with heat or thermocontrols 16 and 18. Thermocontrol 16 is 
a monofunctional control which controls the addition of heat to the 
microcavity component 12 while thermocontrol 18 is a bifunctional control 
which controls both the addition of heat and the withdrawal of heat from 
the hydride component 14. Thus, the temperature of the hydride component 
14 can be regulated in accordance with the pressure of the hydrogen in the 
microcavity component 12 so that the pressure of hydrogen within said 
hydride component remains substantially constant. Heat energy is supplied 
to thermocontrols 16 and 18 from a common heat source 20 which in an 
energy generating apparatus would be waste heat from the apparatus. From 
heat source 20 heat is supplied to the thermocontrols 16 and 18 via heat 
supply line 22 having branches 24 and 26 going to components 16 and 18 
respectively. From the thermocontrols 16 and 18 heat is conducted by heat 
supply lines 28 and 30. Line 28 supplies heat to heating element 32 in 
component 12 and line 30 supplies heat to heat exchanger 34 in component 
14. 
For an energy utilizing apparatus the heat is generally supplied as a 
heated fluid. Thus the supply lines, the heating element and the heat 
exchanger comprise hollow tubes in which this heated fluid flows. 
In both energy utilizing apparatuses and other apparatuses the heat energy 
could be supplied as electrical energy and thus heat source 20 would be a 
source of electrical energy and heat supply lines, 22, 24, 26, 28, and 30 
would represent electrical conduits. Heating element 32 and heat exchanger 
34 would include resistance elements capable of releasing heat upon the 
flow of electric current. In the event that heat is supplied via a fluid, 
heating element 32 and heat exchanger 34 would be connected to exhaust 
lines 36 and 38 respectively for discharge of the fluid from the heating 
element 32 and heat exchanger 34. In the event heat is supplied as 
electrical energy, lines 36 and 38 would represent electrical connections 
allowing for a complete circuit. The heat exchanger 34 in component 14 is 
also connected to a coolant supply source 40 via lines 42 and 44. 
Interspaced between lines 42 and 44 is thermal control 18 which in 
addition to the control of heat to heat exchanger 34 also controls the 
flow of coolant to heat exchanger 34. Line 44 is connected to heat 
exchanger 34 and heat exchanger 34 is also equipped with a coolant exhaust 
line 46 for discharging exhausted coolant from the heat exchanger 34. 
Alternately the exhausted coolant could be recycled back to coolant supply 
40 via line 48 shown in phantom. 
Hydrogen gas released from component 12 is supplied to component 14 and 
apparatus 10 and hydrogen gas released from component 14 is supplied to 
apparatus 10. Both of these supply systems are accomplished by a series of 
conduits having flow control valves to control the flow of hydrogen. 
Conduit 50 supplies hydrogen gas to conduits 52 and 54. Conduit 52 leads 
to flow control valve 56 and from flow control valve 56 hydrogen gas flows 
through conduits 58 and 60 to apparatus 10. Additionally hydrogen gas is 
supplied to component 14 from component 12 via conduit 54, flow control 
valve 62 and conduits 64 and 66. Hydrogen gas from component 14 is 
supplied to apparatus 10 via conduits 66, 68, flow control valve 70, 
conduit 72 and conduit 60. 
The microcavity storage component 12 consists of a large plurality of 
microcavities filled with hydrogen gas at pressures up to 10,000 psi. The 
microcavities generally are from about 5 to about 500 microns in diameter. 
The walls of the microcavities are generally from about 0.01 to about 0.1 
that of the diameter of the microcavities. 
Generally the microcavities are microspheres. Microspheres, however, can be 
sintered together to form porous structures having both interconnecting 
pores and closed micropores. The interconnecting pores provide access to 
the closed microcavity pores throughout the sintered structure. 
In the form of individual microspheres, the filled microspheres may be 
moved from operation to operation like a fine sand or suspended in gas or 
fluids for transportation. Porous structures, however, offer the advantage 
of simpler handling. For example, porous cannisters of sintered 
microspheres could be filled and later inserted in tubes which are 
equipped with an outlet through which the hydrogen would be released. 
Hollow microspheres can be made of plastic, carbon, metal, glasses or 
ceramics depending upon the performance characteristics desired. Generally 
the microspheres will be made of silicate glasses such as Emerson-Cuming 
SI grade high silica containing microspheres. 
Under high hydrogen pressures and elevated temperatures hydrogen will 
diffuse into the microcavities. When stored at normal temperatures and 
under atmospheric pressure the hydrogen remains inside the microcavity 
under high pressure. Upon reheating the microcavity the hydrogen is caused 
to diffuse outside the cavity and is available for utilization by the 
apparatus 10. The time periods for diffusion into and diffusion out of 
glass microspheres are estimated by the following equations: 
##EQU1## 
where t.sub.I =Diffusion in period (sec); x=wall thickness (mm); r=radius 
of the microsphere (cm); K=hydrogen permeability [cm.sup.3 (STP) 
mm/sec.cm.sup.2 (cm of Hg)]; T=temperature (.degree.K.); P.sub.0 =pressure 
outside the microsphere (atm); P.sub.i =pressure within the microshpere 
(atm). 
and 
##EQU2## 
where P.sub.1 =initial pressure inside the microsphere; P.sub.2 =internal 
pressure at time t.sub.0 ; t.sub.0 =Diffusion out period (sec). 
The following general assumptions are implicit in the use of the above 
equations. 
1. Uniform glass composition. 
2. Uniform microsphere size and wall thickness. 
3. Isothermal conditions during hydrogen permeation. 
4. Constant external pressure during diffusion. 
Both of these equations can be similarly derived and in the interest of 
brevity only the derivation of equation 1 is herein described. 
Equation 1 is premised upon equation 3 relating to hydrogen permeability in 
silicate glasses incorporating glass composition and temperature. 
##EQU3## 
where K=the hydrogen gas permeability [cc of gas (STP) mm/cm.sup.2 (cm of 
Hg) sec]; M=the mol percent of nonnetwork formers in the glass, e.g., CaO 
and Na.sub.2 0; T=the absolute temperature (.degree.K.). 
Derivation to this above relationship in equation 3 has been observed for 
hollow microspheres having thin walls (1.5 to 1.5 microns). It is 
postulated that this derivation is caused by high internal pressure. 
However, since in the present invention the use of very thin walls is not 
required, it will be assumed that equation 3 expressing the gas 
permeability of hydrogen in silicate gases is controlling. 
Equation 4 expresses the flow of gases using experimentally determined 
permeability constants. Equation 4 is derived from Ficks' Law, a general 
equation for diffusion, by imposing the condition of a constant pressure 
across the glass walls. Under general conditions for filling hollow glass 
microspheres, the pressure outside the spheres is held constant while the 
pressure inside the spheres increases as the spheres fill. Consequently 
the rate of diffusion decreases as the filling proceeds. Ficks' Law for 
diffusion can then be solved for the condition of filling glass spheres 
using experimentally determined permeability constants instead of the 
diffusion coefficient. The derived differential formed is then given by 
equation 5. 
EQU Q/A=(K.DELTA.P)/x (4) 
where Q=the volume of transported gas measured at STP (cm.sup.3 /sec); 
K=the permeability constant [cm.sup.3 (gas at STP) mm/cm.sup.2 sec (cm of 
Hg)]; .DELTA.P=the pressure gradient across the glass wall (cm of Hg); 
x=the wall thickness (mm); and A=the area (cm.sup.2). 
##EQU4## 
where q=the volume of gas transport in time t.sub.I ; A=diffusion area 
(cm.sup.2); t.sub.0 =Diffusion out period (sec); P.sub.0 =pressure outside 
the glass sphere; and P.sub.i =pressure within the glass sphere at time 
t.sub.0. 
Since by definition q is measured under standard temperature and pressure, 
it is simply the mass of diffused gas as indicated in equation 6. 
##EQU5## 
where M=the gram molecular weight of hydrogen. 
Now equations 5 and 6 can be combined to give equation 7. 
##EQU6## 
Pressure within the glass sphere (P.sub.i) at time t.sub.I is a function of 
the mass of hydrogen diffused through the wall according to Equation 7. 
For most gases, the density is directly proportional to pressure. At high 
hydrogen pressures, a compressibility term (Z) must be used according to 
Equation 8. 
##EQU7## 
where R=the gas constant for hydrogen; T=the absolute temperature 
(.degree.K.); V=volume of the glass sphere (cm.sup.3). 
For the purposes of deriving equation 1 the compressibility term is set at 
one and equations 7 and 8 are combined and rearranged giving equation 9. 
##EQU8## 
The hydrogen gas constant (R), using consistent units, is 
6.24.times.10.sup.3 /M. The ratio of the area to volume for a sphere (A/V) 
is 3/r, where r is the radius of the glass sphere. These values were 
incorporated into equation 9 and result in equation 10. 
##EQU9## 
Integration of equation 10 yields equation 11 which upon rearangement gives 
us equation 1. 
##EQU10## 
The permeability of the microsphere wall can be modified by coating the 
wall. Typical coatings would include plastics and metals. Metal coatings 
are of a particular desired utility in that they can be used to reduce the 
permeability of hydrogen from the microsphere at storage temperatures but 
not interfere with the diffusion of hydrogen into and out of the 
microsphere at elevated temperatures during filling the microspheres or 
dispensing of the hydrogen from the microspheres. Metal coatings may be 
applied by electroless and electroplating, chemical vapor decomposition or 
centrifugal coating techniques. Typical metals suitable for coating 
silicate glass microspheres include aluminum, molybdenum, nickel, copper 
and their alloys. 
The metal hydride hydrogen storage component 14 utilizes a composition 
having at least one metal which will form a metal hydride when exposed to 
hydrogen. Additionally other metals can be alloyed with the primary metal 
to alter the characteristics of the final metal hydride. The base metal 
chosen and any additional metals alloyed with it will be governed by the 
apparatus to which hydrogen is supplied. The criteria governing which 
metal hydride will be used is the hydride heat of formation. If waste heat 
from apparatus 10 is used to heat the metal hydride to liberate hydrogen 
the metal hydride must be capable of liberating hydrogen within the heat 
range of the waste heat in order to conserve energy and not require 
expenditure of additional energy for heating the metal hydride. 
As noted in the background of the invention currently two hydride systems 
are being studied for use in a hydrogen fuel automobile. These systems are 
based upon iron titanium and magnesium alloys. An alloy of equal molar 
amount of iron and titanium has a heat of formation in kcal. of -5.5 per 
mole of hydrogen. Magnesium hydride has a heated formation of -17.8 kcal. 
per mole of hydrogen. By alloying magnesium with nickel or copper the 
heated formation can be made smaller. Typically a nickel alloy having a 
composition Mg.sub.2 Ni has a heated formation of -15.4 kcal. per mole. 
Hydrides which have a high decomposition pressure at low temperatures 
generally have a relatively small value of heat of formation. Magnesium 
nickel hydride has a dissociation temperature of about 300.degree. C. The 
dissociation temperature can be reduced by adding zinc to the alloy giving 
a dissociation temperature of approximately 260.degree. C. Other metals 
having usable heats of formation which may be used to form the metal 
hydride include vanadium, niobium, palladium and an alloy "Misch metal". 
Also known to form hydrides are potassium, uranium, zirconium, calcium, 
lithium and cerium; however, they do have a large value of heat of 
formation. 
Iron titanium hydride is heavier than magnesium nickel hydride; however, 
since iron titanium hydride has a heat of formation of only -5.5 kcal. the 
dissociation temperature of iron titanium hydride is only 25.degree. C. 
For use in apparatuses 10 which utilize waste heat to liberate the 
hydrogen from the metal hydride, iron titanium hydride is the preferred 
metal alloy. Heating this hydride at modest temperatures will cause it to 
decompose and supply hydrogen at pressures of from about 100 to about 1000 
psi. 
The efficiency of the metal hydride is also dependent upon the surface area 
of the metal. The surface area can be greatly improved by cycling the 
metal through a series of hydride formation hydrogen liberation cycles. 
Thus the efficiency of the metal hydride as a hydrogen absorber or 
hydrogen liberator is increased with use. Initially, the hydride is primed 
by exposing it to several cycles of hydride formation-dissociation. 
A useful property of the metal hydrides is that on a volume basis they can 
contain more hydrogen than cryogenic liquid hydrogen. Microspheres can 
contain almost as much volume of hydrogen as cryogenic hydrogen; however, 
as compared to the metal hydrides, the microspheres are able to effect 
this storage of hydrogen in a smaller unit weight. 
For further illustration of the invention in the remainder of this 
specification (a) the hydrogen utilization apparatus 10 will be 
illustrated by a combustion engine used to propel a vehicle most 
specifically an automobile; (b) the microcavity hydrogen storage component 
12 will be microspheres; (c) the metal hydride storage component 14 will 
be iron titanium hydride. FIG. 2 shows an overall schematic for the 
utilization of hydrogen from production to power generation. 
A hydrogen production plant 74 produces hydrogen by one of several methods. 
For example, water could be electrolized using conventional power systems, 
such as solar, fossil fuel or nuclear generation means. Other processes 
also may be available in the future such as radiochemical or 
thermochemical processes for hydrogen generation. In any event, water is 
converted to hydrogen and oxygen and the waste heat from this conversion 
is used to encapsulate the hydrogen in microspheres in an encapsulation 
plant 76 which preferably would be located near the production plant. By 
encapsulating the hydrogen at or near the hydrogen production plant there 
are several advantages. One, there is a potential economical gain from 
large scale production; two, waste heat from the production is utilized to 
encapsulate the hydrogen; and three, transportation of hydrogen is 
simplified by inclusion of the hydrogen in microspheres and as discussed 
below this form of transportation achieves a safety advantage. 
After encapsulation the hydrogen can be stored in a long term storage 
facility 78 prior to delivery to a consumer. Since the hydrogen gas is 
contained in microspheres the pressure in any tanks used to hold the 
microspheres is much less than the pressure would be in tanks if the 
hydrogen was stored as either a liquid or a gas. This offers the advantage 
of reducing to a negligible level embrittlement of the storage tank or 
storage lines by hydrogen. For long term storage, storage tanks could be 
cooled to further prevent escape of hydrogen from the microspheres. 
After storage the microspheres would be transported by a transporter 80 to 
regional service station dispensing units 82. The transportation of the 
microspheres could be effected by transporting tanks of microspheres on 
trucks, ships, railroad tank cars, etc. or the microspheres could be 
slurried in a transfer fluid such as nitrogen or air and transported by 
the fluid within a pipe line. At the receiving end of the pipe line the 
microspheres would be separated from the fluid using a cyclone separator 
or the like. 
At the service station dispensing units 82 hydrogen from the microspheres 
could be used in hydride priming operations shown as block 84 and 
discussed above. However, the primary purpose of the service station 
dispensing unit 82 would be to dispense the hydrogen containing 
microspheres to a vehicle 86. On board the vehicle 86 there would be a 
microsphere storage tank 88 which is filled with the microspheres. 
The hydrogen contained in the microsphere storage tank is utilized as a 
fuel source for the vehicle engine 90 and as a charging source for the 
metal hydride located in storage tank 92. The vehicle engine 90 burns the 
hydrogen and uses the power derived from the hydrogen to propel the 
vehicle. The waste product from this process is water; thus, completing 
the ecological cycle. It is further conceived that after the microspheres 
are emptied of their hydrogen they can be recycled to the encapsulating 
plant for refilling. 
As shown in FIG. 3 a vehicle 86 having an engine 90 is equipped with a 
microsphere storage tank 88 and a metal hydride storage tank 92. The 
storage tank 88 is filled with microspheres 94 and the storage tank 92 is 
filled with a metal hydride composition 96. Storage tank 88 has an opening 
98 equipped with a cap allowing access to the tank for recharging the tank 
by filling the tank with a fresh supply of microspheres 94. 
Within the interior of tank 88 is a heating element 102. Heating element 
102 is a hollow tube in which hot gases pass through. Within the interior 
of tank 92 is heat exchanger 104 also having a hollow passageway for hot 
gases and in addition a second passageway for cooling fluid. An exhaust 
pipe 106 attaches to the exhaust manifold of engine 90 and conducts hot 
gases from the engine. A branch conduit 108 leads from exhaust pipe 106. 
Down stream from branch conduit 108 is a diverter valve 109 which when 
closed diverts exhaust gases in exhaust pipe 106 into branch conduit 108. 
Branch conduit 108 connects to two thermal controls, thermal control 110 
controlling the flow of hot gases to heating element 102 and thermal 
control 112 controlling the flow of hot gases to heat exchanger 104. An 
exhaust pipe 114 leads from heating element 102 and feeds into exhaust 
pipe 106 down stream of the diverter valve 109. Likewise an exhaust pipe 
116 leads from heat exchanger 104 to exhaust pipe 106. 
Vehicle 86 has a radiator 118 for cooling engine 90. Integrated into 
radiator 118 are heat exchange pipes 120 which connect to coolant supply 
line 122 and coolant return line 124. Coolant flows through line 122 to 
thermal control unit 112. From thermal control unit 112 the coolant flows 
through the heat exchanger 104 in metal hydride tank 92 and then returns 
to the heat exchange pipes 120 via return line 124. 
The metal hydride storage tank 92 has an opening 126 to which is attached 
hydrogen conduit 128. Conduit 128 connects to hydrogen flow valve 130. On 
the outlet side of flow valve 130 is hydrogen conduit 132 which connects 
to engine supply conduit 134. Microsphere storage tank 88 has an opening 
136 to which a conduit 138 is attached. Conduit 138 leads into two branch 
conduits 140 and 142. Branch 140 connects to flow valve 144 and on the 
outlet side of flow valve 144 is conduit 146 which connects to engine 
supply conduit 134. Branch conduit 142 connects to flow valve 148 which 
has an additional conduit 150 attached to its outlet side which further 
connects to conduit 128. 
Also connected to conduit 138 is conduit 152 having a two way flow valve 
154. Flow valve 154 is connected to a small hydrogen gas reservoir 156. 
A master control 158 is connected to the engine 90, thermal controls 110 
and 112, the flow valves 130, 144, 148 and 154, and diverter valve 109 by 
appropriate control line all collectively identified by the numeral 160. 
Pressure sensing units 162, 164, and 166 are located in conduits 128, 138, 
and gas reservoir 156 respectively. These pressure sensing units are also 
connected to master control 158 by control line all collectively 
identified by the numeral 168. 
In use, for engine start up, flow valves 144 and 154 are open upon command 
by the master control 158 allowing the residual hydrogen gas in tank 88 
and the hydrogen gas in reservoir 156 to flow to the engine there to be 
utilized as fuel. After several minutes engine 90 reaches its operating 
temperature and the exhaust gases expelled by engine 90 become quite hot. 
Master control 158 signals diverter valve 109 to close and thermal control 
unit 112 to open allowing the hot exhaust gases to flow through heat 
exchanger 104. The heat exchanger heats up the metal hydride within tank 
92 causing hydrogen to be released from the metal hydride. Flow valve 130 
is open and hydrogen is fed to engine 90 from the metal hydride tank 92. 
Thermal control 110 is now opened by master control 158 allowing hot gases 
to pass through heating element 102 which initiates release of hydrogen 
from the microspheres 94. 
As the flow of hydrogen being released from tank 88 increases, the flow of 
hydrogen from reservoir 156 is halted and reservoir 156 is repressurized 
to a predetermined level sensed by pressure senser 166. Valve 154 is then 
closed trapping a fresh quantity of hydrogen in reservoir 158 which will 
be used for the next engine start up. Depending on the fuel needs of the 
engine, master control 158 opens and closes thermal controls 110 and 112 
and diverter valve 109 thereby governing the amount of hot gases passing 
heating element 102 and heat exchanger 104 which in turn governs the 
release of hydrogen from tanks 88 and 92. 
As the metal hydride in tank 92 becomes depleted of hydrogen a pressure 
drop in tank 92 is signaled by pressure sensing unit 162 and master 
control unit 158 signals thermal control 112, stopping the flow of hot 
gases through heat exchanger 104 and starting the flow of coolant through 
the heat exchanger 104. This initiates the removal of heat from tank 92 
and flow valve 130 is closed and flow valve 148 is opened allowing 
hydrogen in tank 88 to pass to tank 92 for regeneration of the metal 
hydride. 
An additional advantage of the invention is that a large portion of the 
hydrogen used to fuel the vehicle is stored in microcavity hydrogen 
storage achieving a safety factor. It is known that highly explosive gases 
can be stored in microspheres because the spheres effectively quench the 
spread of flame necessary to maintain an explosion. If a vehicle carrying 
a large supply of hydrogen encapsulated in microspheres should get in an 
accident and the microsphere storage tank is ruptured, the hydrogen would 
not be released but would be safely retained inside the individual 
microspheres. 
In an alternate embodiment shown in FIG. 4 hydrogen is delivered to an 
apparatus 170 utilizing a metal hydride hydrogen storage hydrogen supply 
component 172 is series with a microcavity hydrogen storage hydrogen 
supply component 174. The metal hydride component 172 is connected via 
lines 176 to microcavity hydrogen component 174. Interspaced in line 176 
is a control valve 178. A second line 180 connects the microcavity 
hydrogen component 174 to the hydrogen utilizing apparatus 170. 
Interspaced in line 180 is a second control valve 182. 
The component 172 contains a metal hydride 184 identical to hydrides as 
previously described. Component 174 contains a hydrogen microcavity 
storage 186 such as microspheres as previously described. Component 172 
includes a heat exchanger 188 containing a heating portion 190 and a 
cooling portion 192 also identical to similar components as previously 
described. Component 174 contains a heater 194 as previously described and 
both heating element 190 and heater 194 are supplied with heat from a heat 
source 196 similar to that previously described. Cooling component 192 is 
supplied with coolant from coolant reservoir 198, again as previously 
described. 
Hydrogen can be supplied to apparatus 170 directly from the microcavity 
storage component 186 by opening valves 182. Alternately hydrogen can be 
supplied to the apparatus 170 from the metal hydride component 172 by 
opening both valves 178 and 182. The metal hydride component 184 is 
recharged from the microspheres 186 by opening valve 178 while valve 182 
is closed. The system can also utilize appropriate controls similar to 
those previously described for monitoring and regulating the flow of 
hydrogen. 
For initial start up of the apparatus 170, when microcavity component 174 
is charged with microspheres as the hydrogen supply component 186, the 
dead spaces inbetween the individual spheres can serve as the residual 
hydrogen storage reservoir. Thus, the microcavity component 174 can 
contain hydrogen at two different pressures--the first being high 
pressurized hydrogen inside of the microcavities, the second being low 
pressured hydrogen outside of the microcavities. This type of hydrogen 
reservoir can also be used with the other embodiments previously 
described. 
In yet another embodiment of the invention only a single storage tank is 
used. Located within this storage tank would be both the metal hydride and 
a microcavity storage systems. This embodiment offers the advantage of 
having the metal hydride in immediate proximity to the microcavity which 
allows for direct exchange of hydrogen from the microcavities to the metal 
hydride and additionally, the heat released from the metal hydride as it 
absorbs hydrogen is used directly to heat up the microspheres to stimulate 
them to release additional hydrogen. 
Typical glass microspheres will release hydrogen at slightly below 
175.degree. C. Thus in this system the metal hydride chosen would be one 
having a somewhat elevated dissociation temperature. Thus the energy 
released upon absorption of hydrogen would be of a slightly higher 
temperature than the temperature necessary to free the hydrogen from the 
microcavity storage. For this type of system metal hydrides based upon 
magnesium or one of its alloys are preferred.