Closed loop reactant/product management system for electrochemical galvanic energy devices

The present invention teaches a closed loop energy system including means capable of managing both the cooling cycle and the fuel/oxidant gas flow in conjunction with a fuel cell. The system includes a plurality of galvanic cells, gas flow conduit means, internal fluid flow conduit means, heat exchanger means, liquid-gas separator means, and gas repressurization means.

This invention is directed generally to a closed loop system for the 
management of hydrogen-oxygen fuel cells. More specfically, this invention 
is directed to a low temperature hydrogen-oxygen fuel cell requiring 
cooling water and gas flow management. 
BACKGROUND OF THE INVENTION 
Fuel cells are galvanic systems which operate following similar 
electro-chemical principles as in conventional storage batteries. There is 
a positive and negative electrode separated by an ion-conducting 
electrolyte adapted to carry current generated by a catalyzed chemical 
reaction. The fuel cell, however, has a theoretically infinite power 
output capability, as long as fuel and oxidant are continuously fed to the 
system for reaction. For example, the current flow in the traditional 
hydrogen-oxygen fuel cell is generally provided by the flow of electrons 
associated with the passage of an ion through an intervening electrolyte 
medium. 
There are generally three distinct types of low temperature hydrogen-oxygen 
fuel cells: the solid polymer proton exchange membrane fuel cell, the 
alkaline fuel cell, and the phosphoric acid fuel cell. All of these types 
generally operate at below about 250.degree. C., in aqueous systems. 
Electrical energy is produced by the catalyzed reaction between hydrogen 
and an oxidizing gas, usually pure oxygen, with the movement of an ion, 
i.e., a proton or hydroxyl ion (OH.sup.-), through an electrolyte 
connecting the positive to the negative electrode. In the alkaline fuel 
cell, the electrolyte is highly concentrated (at least about 30 wt. %) 
aqueous potassium hydroxide solution, the concentration determining the 
maximum operating temperature. This hydroxide electrolyte is generally 
maintained within a solid matrix, including, for example, asbestos, 
together with a catalyst. The catalyst can be, in addition to the noble 
metals, nickel, silver, certain metal oxides and spinels. 
The second type of low temperature fuel cell is the phosphoric acid fuel 
cell, which utilizes concentrated phosphoric acid as the electrolyte. This 
fuel cell operates at temperatures in the range of between 150.degree. C. 
and just over 220.degree. C. The concentrated acid electrolyte is 
preferably at approximately 100% concentration, and is retained in a solid 
matrix, such as silicon carbide(SiC). The electro-catalyst, which 
impregnates both the anode and the cathode, can be platinum or other such 
noble metals. 
An efficient low temperature system, which also operates at temperatures 
below the boiling point of water, includes a solid polymeric proton 
exchange membrane between the fuel cell electrodes. The membrane is formed 
from, for example, perfluorocarbon materials sold, for example, under the 
trademark "NAFION".RTM. by E. I. DuPont De Nemours. A noble metal catalyst 
is also required for most polymeric membrane type of fuel cells. 
Commonly available solid polymer electrolyte fuel cells require input of 
reactant gases, usually a hydrogen fuel and an oxidant, generally oxygen 
or air, and of water, for cooling and for maintaining the electrolyte 
membrane. 
The cooling systems for the solid polymer electrolyte fuel cells are of two 
types: the water flow, or pass-through, type, where cooling water from 
outside the cell is provided for indirect heat exchange from impervious 
conduits within the cell; and the passive, or wicking, type of cell, by 
evaporative cooling, wherein water is caused to evaporate from the anode 
support plates, which are formed to have a large surface area. 
For both types of cooling systems, the solid polymer electrolyte membrane 
must be kept moistened with water; otherwise the membrane will dry out, 
and become inefficient in operation as well as structurally weakened. 
Water is generally carried from the fuel, or hydrogen, side of the 
membrane, together with the proton, through the membrane, thereby tending 
to dry the anode side of the membrane, and causing cracking of the 
membrane. In operation, additional water must thus be supplied with the 
hydrogen, to compensate for the water removed. 
One system to improve cooling of the fuel cell, while at the same time 
maintaining humidification of the fuel side of the membrane, is shown, for 
example, in U.S. Pat. No. 4,649,091. 
As commercially available, the so-called "fuel cell" is actually a stacked 
configuration of a plurality of cells each having an anode and a cathode, 
with a solid electrolyte membrane between them, and passages for fuel and 
oxidant gas. To maintain a continuing operation of such a stack of cells 
requires a system that provides sufficient cooling to prevent overheating 
of the system and means to provide the fuel and the oxidant, in a managed 
system to maintain a sufficiently long operating time between shutdowns. 
In some conventional fuel cell stacks, the hydrogen and oxygen gases are 
delivered to the stack in excess of that needed to support the 
electro-chemical reaction. There is thus a continuous flow through the 
stack, and an exhaust from the stack by which product water is removed and 
any inert gases are vented together with the excess hydrogen and oxygen. 
Generally, the great majority of the product water is removed with the 
oxygen purge, whereas only a relatively small amount of condensation is 
removed along with the hydrogen purge. Generally, the fuel and oxidant 
gases first pass through humidification cells within the cell stack. The 
gases are there saturated with pure water vapor in order to prevent 
dehydration of the ion-conducting membrane. The humidified gases are then 
passed through the anode and cathode chambers, respectively, of the cells 
within the stack, the cells being fed in parallel; and the excess gases 
are then vented from the final cell. Although the gas and liquid flow 
through the stack system is in parallel, i.e., through the individual 
cells, the electrical connection between the individual cells is 
conventionally in series. 
The cooling water within the stack must be extremely pure, e.g., deionized 
water having a high resistivity. The cooling water passes through an 
external indirect heat exchanger where the heat is transferred to, for 
example, a parallel or countercurrently flowing stream of raw water. This 
same internal cell cooling water has been conventionally used to humidify 
the gas streams within the humidification stage of the cell stack. 
SUMMARY OF THE PRESENT INVENTION 
The present invention provides a means to manage both the cooling cycle and 
the fuel and oxidant gas flow of a fuel cell stack, in a simple and 
self-adjusting manner. The result of this careful management of such a 
system is to provide a greater campaign duration for the operation of the 
fuel cell before shutdown is required, and simultaneously to conserve fuel 
and oxygen supply for a system of limited fuel capacity, such as on board 
a submarine. By maintaining all of the products within a closed system, 
the present invention also precludes the need for additional ballast 
control, e.g., for a submarine or aircraft. Finally, the management system 
further preferably provides for external humidification of the system 
without risking contamination of the fuel and oxygen gases, using pure 
product liquid. 
It is therefore an object of the present invention to provide an improved 
water management system for a low temperature fuel cell stack. 
It is the further object of this invention to provide an improved gas flow 
management system in combination with a water flow management system to 
provide necessary humidification of the fuel cell electrolyte and while 
maintaining a sufficiently low concentration of inert diluent within the 
fuel cell system to maintain a long operating period between shut-downs. 
It is yet a further object of this invention to provide a closed system for 
a fuel cell wherein all reactants and products are maintained within the 
system without loss.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention, generally, and the systems shown in the figures of 
the drawings herewith, are intended to provide a reliable and efficient 
air-independent power system for such enclosed uses as submersible 
vehicles, submerged underwater installations, or space vehicles, using 
hydrogen and oxygen as the fuel and oxidant for a fuel cell power source. 
Most preferably, the present closed loop management system is most 
effectively used within an enclosed package requiring only hydrogen and 
oxygen makeup gas input, external indirect heat exchange, electric power 
output, and electronic inputs and outputs. 
Referring to the system design shown schematically in FIG. 1, a fluid and 
pressure-tight chamber, the walls of which are indicated by the numeral 
10, contains a fuel cell power source, generally indicated by the numeral 
12, of a relatively low operating temperature type. Most preferably the 
proton exchange membrane type fuel cell is utilized, which operates below 
the boiling point of water, generally not above 70.degree. to 75.degree. 
C. There is no requirement to maintain a liquid electrolyte between the 
anode and cathode of each cell. 
As most generally now configured, the fuel cell power sources are provided 
in the form of stacks of fuel cells, literally stacked one next to the 
other and having anodes and cathodes arranged in electrical series. The 
flow of reactants, i.e., hydrogen and oxygen, to the individual fuel cells 
is generally arranged in parallel. As will be discussed below, it is most 
effective to utilize a plurality of separate stacks which can continue to 
operate jointly, albeit at a lower power level, even if a cell in one or 
more of the individual stacks is incapacitated. By virtue of the 
configuration of the stacks, the obstruction or inactivity of any 
individual cell will inactivate the entire stack within which such cell is 
located. 
The power source container 10 is a compact modular assembly which can be 
inserted, as a unit, into a system requiring a power source, either as the 
primary source or as a back-up source of power. 
The closed loop management system of the present invention is discussed 
below in terms of a solid polymer membrane electrolyte system which 
requires both cooling and humidification water. In this system, the supply 
tanks for the hydrogen reactant and the oxidizing gas, e.g., oxygen, are 
located externally of the module container. These fuel and oxidizer tanks 
can be of standard, or conventional, design such as so-called "gas 
bottles", containing the gases at pressures of up to about 2200 to 2500 
psig. These bottles are generally equipped with manual valves and can be 
connected by known means through the power module end plate into the 
module. 
Each of the oxygen and hydrogen gas make-up supply lines 14, 16, 
respectively, include a solenoid operated valve 17, 18 and a gas pressure 
sensor (or indicating gauge) 20,21 measuring the gas pressure in each 
line. Each line further comprises a remotely resettable pressure regulator 
24,25, followed downstream by a further gas pressure sensor 27,28. The 
incoming make-up gas lines 14,16 pass into water reservoirs 30,31; the gas 
enters the reservoirs at a lower level, below the water level, so as to 
bubble through any liquid therewithin for humidification of the gas. The 
water reservoirs 30,31 are both pressure-tight so as to maintain the gas 
line pressures. 
The gas feed lines 33,34 between the reservoirs 30,31 and the fuel cell 
stack 12, include each a filter 37,38, to remove any solid particles, 
before passing through a pressure sensor 39,40, respectively, before 
entering the fuel cell stack 12. The design of the flow passages within 
the fuel cell stack is determined by the particular manufacturer of the 
fuel cells and is not an element of this invention. 
Useful such fuel cell stacks include the Ballard Fuel Cell Stack, having an 
overall volume of approximately 1.5 cubic feet and weighing about 100 
pounds. Such a fuel cell stack is stated by the manufacturer to contain 42 
cells and is capable of generating 5 kilowatts utilizing hydrogen and 
oxygen. The fuel cell membrane electrolyte can be a sulfonated 
fluorocarbon, such as NAFION, manufactured by DuPont. 
Such a fuel cell can operate continuously at an internal temperature of 
about 70.degree. C., with respect to the cooling water, but can start-up 
at room temperature, producing about 85% of rated power at that 
temperature at full constant voltage. The stack can warm up within a few 
minutes from the heat generated by the fuel cell. Accordingly, the cooling 
water is not required to be directed to the heat exchanger, until the 
desired operating temperature is reached. The fuel cell can be operated 
continuously or intermittently at the full range of power from 0% to 100%. 
By replacing NAFION with a new sulfonated fluorocarbon membrane made by Dow 
Chemical, current densities have been increased to 4000 amps per sq. ft. 
at cell voltages in excess of 0.5 volts per cell, thus giving power 
density in excess of 2 kilowatts per sq. ft. 
Other useful fuel cells of the solid membrane electrolyte type are shown, 
for example, in U.S. Pat. Nos. 4,175,165; 4,795,536; 4,678,724; and 
4,826,741. Although the latter patent obtains hydrogen from a metal 
hydride source, the fuel cell operating on the generated hydrogen gas 
would be effective in the present system. 
After flowing through the fuel cell stack, the excess remaining hydrogen 
and oxygen gases exit the stack through outlet piping 50,51, respectively. 
The pressure of these excess gases must be increased before the gas can be 
recycled. In this embodiment, the gases are each repressurized by the gas 
recycle pressure pumps 54,55. 
These recycle pressure pumps 54,55 can be powered by the electrical output 
from the fuel cell, as part of the "hotel load" on the fuel cell. As an 
alternative to such an electrically powered recycle pump, an eductor type 
system can be employed, utilizing the gas flow from the gas supply 
bottles. This reduces the usage of electricity without in any way diluting 
or contaminating, or otherwise interfering with the reactant gas flow. 
A check valve 57,58 is provided in each return gas line 50,51, 
respectively, to prevent any backflow; and a gas flow sensor 60,61 is 
provided in each line 50,51 to measure the recycle gas flow in each line. 
The recycle gas lines 50,51 then connect to the upper portion of the water 
reservoirs 30,31, where the recycle gases are mixed with the make-up gases 
from lines 14 and 16. 
In this embodiment, the upper portion of each of the water reservoirs 30,31 
comprises the free space above the water level in the reservoir, and each 
such free space acts as a liquid-gas separator, any liquid water drops out 
while the gas is resident in the free space, separating from the gas 
streams, and falling into the lower reservoir section of the vessel. There 
is free gas space above the liquid level, from which the now liquid-free, 
but humidified, gas enters the inlet lines 33,34 to the fuel cell stack 
12. It is understood that other designs, including separate liquid-gas 
separators, e.g., centrifugal separators, can be used, in vessels separate 
from the reservoirs. 
Cooling water must be pure deionized water. Only a relatively small 
quantity of water is required at start-up in the water reservoirs 30,31. 
The cooling water is pumped from the oxygen water reservoir 30, by a water 
pump 65, and through lines 64 and 66 into the cooling system within the 
fuel cell stack 12. The flow of cooling water is measured, preferably at 
the exit from the fuel stack, by an in-line flow sensor 68. Water exits 
from the cooling system of the fuel cell stack through a water recycle 
line 70, at which exit point the water temperature is measured by 
temperature sensor 72. The water flows through line 70 to a location 
outside of the power package envelope 10, passing through an indirect heat 
exchange coil 75, which is in contact with any suitable source of cooling 
medium, before being returned to the oxygen-side water reservoir 30. For 
example, on a submersible or other sea-going vessel, the heat exchanger 
would be in contact with raw seawater. In other situations, cooling gases 
or other liquids, passing through (or over) a suitable heat exchange 
surface, can be utilized. The design of the indirect heat exchanger 75 is 
not a part of this invention, and any suitable design capable of cooling 
the recycling cooling water to below about 40.degree. C. can be used. 
The water added to the hydrogen reservoir 31 during operation is a result 
of condensation from the recycled hydrogen gas. If desired, additional 
water can be provided through initial feed/drain line 81, or excess water 
can be drained, especially from the oxygen reservoir 30, in the event a 
lengthy operating campaign causes the product water level in that 
reservoir 30 to increase so that there is inadequate free space below the 
gas lines 50,33. 
Referring now to FIG. 2, a substantially similar system is disclosed, 
except that the makeup hydrogen and oxygen gases are fed directly from the 
gas supply 4,5 into the stack, without being humidified in the water 
reservoirs 130,131. This alternative system requires a humidification 
section in each fuel cell stack to insure against drying out the membrane 
electrolyte. This is especially onerous in those situations where separate 
fuel cell stacks are operated within the module package; a separate 
humidification section would be required for each of the separate stacks 
in the embodiment of FIG. 2. By utilizing the system of FIG. 1, wherein 
all makeup gases are prehumidified, each of the stacks can be further 
reduced in size and weight by omitting the humidification section. As the 
water reservoir 130 remains a feature of this system with or without the 
prehumidification effect, the reduction in weight and volume of the fuel 
cell stack and the overall power package is clear. 
By eliminating the internal humidification sections within each cell, for 
example, in a system utilizing three separate fuel stacks, approximatley 
20% additional power cells can be obtained within the same volume and 
weight. 
In addition to improving the efficient use of a fuel cell stack power 
source, the closed loop system of the present invention permits a closer 
management of each of cooling water, product storage and gas flow through 
the fuel cell stack. A preferred aspect of any such system is the use of a 
system-wide sensing network, having a central logic control module for 
reading and reacting to data remotely provided by individual sensory 
elements located throughout the system. As is shown by the monitoring and 
control system block diagram of FIG. 3, data collected by the sensing 
units located within the closed loop system are fed to a central 
programmable controller, which provides output data to the onstream 
operator as well as providing diagnostic information during and after 
operation of the power pack. In addition, the programmable controller 
provides a fail/safe response to the data, individually or combined, 
received from the various sensing elements, in the event the data are 
outside of the prescribed range of values. 
Specifically, the preferred logic control system receives sensory data 
input from the input pressure sensors 20,21 for the oxygen/hydrogen makeup 
supply gases, respectively, from upstream of the initial pressure 
regulators 24,25, as well as from downstream of the pressure regulators, 
by sensors 27,28. It has been found, however, that these sensory locations 
are not among those required to optimize the system. 
Those critical sensory locations for providing data to the microprocessor 
system, which are the minimum necessary to achieve automatic 
microprocessor control of the closed loop fuel cell power package of this 
invention, include pressure sensor 39,40 in the hydrogen and oxygen fuel 
cell inlet lines, respectively, immediately upstream of the inlet to the 
fuel cell stack. The other necessary sensing locations for providing input 
data to the central cotnroller include the following: the gas flow sensors 
60,61 (volumetric measurement at STP) in the recycle oxygen and hydrogen 
exit lines 50,51, respectively, from the stack 12, immediately downstream 
of the repressurization pumps 54,55; the temperature sensor 72 and water 
flow sensor 68 measuring the cooling water outlet temperature and 
volumetric flow rate in the water exit line 70 from the fuel cell stack 
internal cooling system; and the water level within the water knockout 
reservoirs 30,31 as measured by the water level indicators 90,91, 
respectively. These data signals are sent to the central logic control 
system. 
Although the primary concern with respect to the water level in the 
reservoirs 30,31 is flooding, of the water reservoirs 30,31, and thus 
blocking of the gas flows in and out of the fuel cell through the oxygen 
and hydrogen gas lines 33,50,34,51, it is also important to maintain a 
minimum water level in order to insure there is adequate cooling and 
humidification, or water saturation, of the gases flowing into the fuel 
cell stack. As previously explained, humidification is necessary in order 
to maintain the integrity of the membrane electrolyte. 
For security reasons, a flood sensor 93 is preferably provided to indicate 
if there is any liquid flooding into the powe package container 10 and 
hydrogen gas detectors to note the presence of explosive hydrogen gas 
within the package container 10, outside of the fuel cell stack closed gas 
loop. Finally, the control system must have input from the sensor elements 
125 measuring total fuel cell stack voltage output as well as voltage 
output measurements for selected individual groups of cells within the 
stack; the selection of the groups of cells to be combined to check 
voltage output is determined by each individual manufacturer, who provide 
voltage taps on the exterior of the fuel cell stack shell 12, for such 
data sensing. Generally, a single, multi-pin electrical outlet is provided 
for the output tap for the various voltage measurements. 
The control system further provides for automatic operation of the system 
so as to shut down the system in the event sensory data indicates 
potentially dangerous conditions. The data are recorded and compared with 
standard values, programmed into the programmable logic controller 120, as 
parameters for the evaluation of the system. Thus, if certain programmable 
values are not met by the received data, the programmable controller is 
set to deactivate this system by activating the following functions: 
disconnecting the electrical load from the fuel cell; closing the solenoid 
inlet gas valves 17,18, thus shutting off makeup oxygen and hydrogen 
gases, respectively, from entering into the system; while continuing to 
leave open the gas recirculation lines 50,51, and 35,34, including 
operation of the recycle pumps 54,55, for a sufficient time to permit the 
removal of condensate from the fuel cell stack, and to lower the fuel cell 
stack temperature by continuing the operation of the cooling water flow by 
maintaining the water pump 65. 
In addition, the controller system is able, by programmable feedback 
operations, to increase makeup gas flow by controlling the pressure 
regulator valves 24,25, and can control the temperature within the fuel 
cell by activating the bypass valve 96 in the cooling water line to pass 
the water flow through the external heat exchanger 75, or through the 
shunt line 98 for recycling directly back to the water reservoir 30. 
The closed loop system herein described is selfregulating over a major 
portion of its operating range. The inlet pressure regulators 24,25 
respond to demand from the fuel cell to provide sufficient flow to 
maintain the desired pressure drop within the system, between the inlets 
39,40 and the fuel cell outlets 50,51, as the gases are converted to 
water. The recycle flow rate is thus determined solely by the action of 
the repressurization pumps 54,55, or other means. 
The repressurization recycle flow pumps 54,55 are generally maintained for 
constant recycle flow during the operation of the fuel cell. Generally the 
recycle is varied only downwardly if the cell is to be operated at idle, 
i.e., at extremely low power outputs, to minimize hotel power 
requirements. 
The container 10, packaging the fuel cell stack and the closed loop system 
is fluid and pressure-tight so as to substantially exclude from within the 
container any pressure changes in the surrounding ambient conditions. All 
piping penetrating the container shell 10 generally pass through the end 
bulkheads 85,86, for providing the necessary inputs and outputs of data, 
control signals, reactants, water and electrical power. 
Suitable microprocessor control systems are conventionally and commercially 
available; such systems are preferably programmable by any of the 
available binary logic programming or operating systems. The central 
processing unit of the controller system must have sufficient memory and 
operating capacity so as to register and record reactant supply pressures, 
total cell voltage output, the voltage output from groups of cells and the 
cooling wate temperature and flow. One such useful system is manufactured 
by Gould Electronics and designated PC-0085. The present system, as 
depicted in the accompanying drawings, requires the ability to register, 
record and react to at least 12 data input sources and must be capable of 
acting upon at least 6 operating devices. 
Other suitable programmable controllers include the TSX17 manufactured by 
Telemecanique; the Omran C-20K programmable controller by Allen-Bradley, a 
division of Rockwell International; the General Electric Company's Series 
90-30 programmable controllers are also usable in the present system. 
The materials of construction for the various plumbing and mechanical 
components useful in the closed loop management system of the present 
invention must be of sufficient structural strength to support and uphold 
the integrity of this system, and must be chemically noninterfering with 
the system. Generally, this requires that none of those materials of 
construction which are in any way exposed to the reactant gases or to the 
cooling water within the system, release free ions into solution or 
otherwise react with hydrogen or oxygen under the operating conditions. 
Useful such materials which are thus inert to the working fluids of 
hydrogen/oxygen and deionized water include the following: 316 passivated 
stainless steel, fluorochlorohydrocarbons, such as Teflon, Viton polymers, 
polycarbonates, and silicon glass. Buna-N polymers and natural rubber, as 
well as all copper-containing metal alloys are expressly excluded. The 
piping connections should be welded and closed with O-ring face seals. 
The reactant gases, preferably at least 99.9% pure hydrogen and medical 
grade oxygen, should be maintained at a pressure of not less than about 
100 psig. Pressurized "bottles", which are commercially available, 
generally are rated at pressures of from about 2000 to 2500 psig. Each of 
these bottles should be provided with manual shutoff valves. In addition 
to such bottles of highly pressurized gases, other means of storing 
hydrogen include, for example, materials which are chemically reactive to 
form hydrogen, such as metal hydrides or methanol, or cryogenic storage 
devices; these are known and do not constitute a part of this invention. 
The solenoid shutoff valves 17,18 are designed to be fail closed, i.e., 
they shut off flow when a power interruption occurs or power is 
intentionally removed. Generally, pressure regulator valves should be 
suitable for use across the full range of pressures of the storage devices 
and the minimum pressure required for fuel cell power production. The 
pressure and flow sensors can either be of the minimum or maximum 
signalling type, or can provide quantitative values on a continuing basis. 
The water reservoirs 30,31 must be capable of withstanding a pressure of 
not less than 150% of the maximum fuel cell pressure. The height-to-width 
ratio of the reservoirs is preferably not less than 1.5, in order to 
provide for the desired free space above the top water level. The oxygen 
reservoir, in which is collected the product water from the fuel cell and 
which holds the deionized cooling water, should have a total volume of at 
least about 0.5 liters of deionized water pe kW-hour output rating for the 
fuel cell stack or stacks, with a free space below the gas lines 34,51 of 
at least about 4 ins. The hydrogen reservoir should hold at least about 50 
mls of water per kW-hour maximum output power rating. Initially, at 
startup, there need be provided in the reservoirs 30,31 only sufficient 
water to provide the required humidification of the reactant gases and 
cooling of the stack. 
The recirculating gas pumps 54,55 in the hydrogen and oxygen recycle lines, 
respectively, must provide a discharge pressure at least sufficient to 
start against the maximum fuel cell rated pressure. The pumps can be any 
of the centrifugal, diaphragm or positive displacement type pumps, formed 
of suitable materials of construction. 
The water recirculation pump similarly can be of any commercially available 
type, again formed from suitable materials of construction to avoid any 
transfer of ions into solution in the flowing cooling water. 
The recirculation pumps 54,55 for the reactant gases, as explained above, 
can be substituted with an eductor-type system utilizng the pressure drops 
and flow between the, e.g., gas supply bottles, and the fuel cell inlets. 
By this means, additional power savings are obtained; generally the flow 
of gases to the fuel cell is more than adequate to provide the needed 
energy for the recirculation pressurization. 
The electrical connections between the various sensory and operational 
locations within the power package container 10 and the microprocessor 
control system 120 are in accordance with conventional standards for 
explosion proof systems. The only requirement, except for suitable 
conductivity, revolves about the safety requirement when dealing with 
hydrogen gas. Generally, commonly available such control systems are 
adequately insulated and of sufficiently low power that there should be no 
danger of explosion, even if hydrogen gas is released into the 
environment. 
The fuel cell stack power output is tapped off through the power connector 
130, passing through the container end plate 86. 
EXAMPLE 
The enclosed modular container system depicted in FIG. 4 was utilized as 
the auxiliary power system for a research submersible. The outer container 
10 had a internal diameter of 15 inches and a total internal length of 72 
inches. The outer shell was capable of withstanding a pressure 
differential of 450 PSI across its walls. 
Hydrogen and oxygen gas bottles at a pressure of 2250 PSIG were attached to 
the gas supply valves 4,5. The fuel cell stack is an available Ballard 
Mark V, 5 kilowatt hydrogen/oxygen fuel cell stack with a solid polymer 
electrolyte. At steady state operation, the recycle hydrogen flow through 
line 51 is 9 liters per minute STP and the recycle flow of oxygen through 
line 50 is 9 liters per minute STP. The repressurization pumps 54, 55 are 
rated to increase the pressure from 28 psig to 30 psig and the water 
reservoirs have a total internal capacity of 10 liters for the oxygen 
reservoir 30 and 1 liter for the hydrogen reservoir 31. The amount of 
water should not be greater than 8 liters for the oxygen reservoir 30 0.75 
liters for the hydrogen reservoir 31. The cooling water flow at steady 
state operation as measured by the liquid flow meter 68 is 6.5 liters per 
minute. When operating in sea water having a temperature of 80.degree. F. 
The heat exchanger has a heat exchange surface area of 57 sq. in. 
The pressure of the reactant gases at the pressure sensors 20, 21 is 
adjusted to be 30 psig. 
This fuel cell system can operate continuously for at least 3 hours 
depending upon the amount of hydrogen an oxygen reactants provided. The 
total volume within the close loop system is sufficiently great that any 
accumulation of inerts which may be present in the reactant gas supply or 
which may result from operation of the system do not accumulate in 
sufficient concentration to interfere with the fuel cells operation. This 
fully enclosed and compact system is thus especially valuable for those 
situations where these attributes are valuable, such as for submersibles 
or spacecraft.