Note: Descriptions are shown in the official language in which they were submitted.
CA 02523640 2005-10-18
TITLE
Fuel Cell Fluid Management System
TECHNICAL FIELD
The present invention relates generally to fluid management systems for fuel
cells.
BACKGROUND OF THE INVENTION
Fuel cells produce electricity from the electrochemical reaction between a
hydrogen-
containing fuel and oxygen. Fuel cell exhaust consists of oxidant and water
and some waste
heat, provided that pure hydrogen is used.
One type of fuel cell is a proton-exchange-membrane (PEM) fuel cell. PEM fuel
cells
are typically combined into fuel cell stacks to provide a greater voltage than
can be
generated by a single fuel cell. Fuel cell stacks are typically provided with
manifolds that
distribute fluid to and collect fluid from all of the constituent fuel cells.
The manifolds are
provided with ports for coupling to external fluid supply circuits, external
fluid exhaust circuits
and external fluid circulating circuits.
The fuel used by a PEM fuel cell is typically a gaseous fuel, and the gaseous
fuel is
typically hydrogen, but may be another hydrogen-containing fuel, such as
reformate. In a
typical PEM fuel cell, a chamber of hydrogen gas is separated from a chamber
of oxidant
gas by a proton-conductive membrane that is impermeable to oxidant gases. The
membrane is typically formed of NAFION~ polymer manufactured by DuPont or some
similar ion-conductive polymer. NAFION polymer is highly selectively permeable
to water
when exposed to gases.
In order for the fuel cell membrane to function properly, it must be hydrated;
in typical
PEM fuel cells, water vapor is continuously added to the fuel supply stream
and to the
oxidant supply stream in order to keep the fuel cell membranes hydrated. Fuel
cells release
more water in their exhaust than they require in their fuel, as hydrogen atoms
and oxygen
atoms combine to produce water in the electrochemical reaction of the fuel
cell. As water
permeates very readily through the membrane separating the fuel and the
oxidant, sufficient
water can return from the oxidant side of the membrane to the fuel side by
simple
permeation as long as the high water concentration on the oxidant side is
maintained.
Fuel cells often operate using air as the oxidant, relying upon the
approximately 20%
oxygen in ambient air. The use of air as an oxygen source requires a flow rate
of air five
times that required for oxygen. When ambient air is used as an oxygen source,
this high
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flow rate dries out the membrane by diluting the water vapor concentration on
the oxidant
exhaust side of the membrane. If water can be recovered from the oxidant
exhaust, the
need for a separate water supply to keep the membrane hydrated for proper
permeation of
hydrogen can theoretically be eliminated.
US patent application 2002/0155328 to Smith describes a method and apparatus
which recovers and recycles water from a fuel cell exhaust and returns the
water to the
supply gases for the fuel cells. Particularly, water vapor is transferred from
the exhaust
gases to one or more supply gases by passing hot humidified exhaust gas over
water
permeable tubes, such that a supply gas flowing through the tubes is
humidified by water
permeating through the tubes and heated by heat conducted through the tubes
from the
exhaust gas. Commonly assigned US patent Pat. No. 6,864,005 to Mossman
discloses and
claims a membrane exchange humidifier, particularly for use in humidifying
reactant streams
for solid polymer electrolyte fuel cell systems.
A drawback of the described apparati in Smith and Mossman is that liquid water
in
one or both of the oxidant exhaust stream and the fuel exhaust stream is not
separated and
removed from the exhaust streams before reaching a membrane humidifier in the
apparatus. The accumulation of liquid water within a membrane humidifier can
clog the
membrane, thereby reducing the effectiveness of the humidifier and the
humidification
method. When the effectiveness of the humidifier is reduced, the fuel cell
supply gases may
not be humidified to the level required for effective power generation in the
fuel cells, and
may lead to drying of the fuel cell membrane. Drying of the fuel cell membrane
is associated
with the creation of holes in the fuel cell membrane, a condition which may
cause the fuel
cell to stop producing electricity. Furthermore, liquid water in a
recirculating fuel stream can
harm fuel circulation pumps, which may lead to failure of the fuel circulation
pump. The lack
of liquid water removal in a humidification apparatus requires that a separate
liquid water
removal apparatus and method be employed in order to provide effective
humidification of
fuel cell supply gases, and in order to avoid damage to fuel circulation
pumps.
A further drawback of the products disclosed in Smith and Mossman is that they
require connecting apparati such as pipes or tubes between the fuel cell and
the
humidification apparatus. Connecting apparati result in heat loss, which may
lead to the
condensing of the water vapor to liquid water within the connecting apparati
or within the
humidification apparatus, thereby reducing the effectiveness of the
humidification apparatus
and method. Furthermore, the condensing of water vapor to liquid water within
the
humidification apparatus increases the amount of liquid water within a
humidification
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CA 02523640 2005-10-18
apparatus and within a fuel circulation pump, and thereby exacerbates the
problems
described above. Furthermore, connecting apparati require space, which
increases the
volume of the system. Furthermore, connecting apparati increase the complexity
of the fuel
cell system, which may increase the cost of the system.
Commonly assigned U.S. Pat. Nos. 6,545,609 and 6,939,629 disclose and claim a
humidification system for a fuel cell. In U.S. Pat. No. 6,545,609, Shimanuki
et al., provide a
humidification system for a fuel cell that includes a humidifier having a
bundled plurality of
tube type hollow thread members made of a water permeable membrane. The
humidifier
transfers a water content contained in a discharge gas, which is emitted from
a fuel cell, to a
supply gas, which is supplied to the fuel cell, when one of the discharge gas
and the supply
gas is passed through the inside of the tube type hollow thread members and
the other one
of the discharge gas and the supply gas is passed through between the tube
type hollow
thread members. Manometers detect a difference in pressure of the supply gas
and the
discharge gas, respectively, between an upper stream side and a down stream
side of the
humidifier. A determination unit determines a generation of clogging in the
humidifier based
on detection signals from the manometers. The products described in these
patents
disadvantageously suffer from clogging of the membranes, and require complex
means for
detecting and dealing with the clogging.
In U.S. Pat No. 6,939,629, Shimanuki et al., provide a humidifying system for
a fuel
cell that includes a fuel cell having an anode and a cathode, the anode being
supplied with a
fuel gas and the cathode being supplied with an oxidant gas so that the fuel
gas and the
oxidant gas chemically react within the fuel cell to generate electricity; a
first humidifier
transferring moisture of cathode exhaust gas discharged from the cathode of
the fuel cell to
the fuel gas through hollow fiber membranes; a second humidifier transferring
moisture of
cathode exhaust gas discharged from the first humidifier to the oxidant gas
through hollow
fiber membranes; and a reduced pressure generating device arranged downstream
of the
first humidifier and between the first humidifier and the fuel cell to mix
part of anode exhaust
gas discharged from the anode of the fuel cell with the fuel gas using
negative pressure
resulting from a flow of the fuel gas. The product described in this patent
disadvantageously
requires connecting apparati between the fuel cell and humidifier and other
components,
which add to system complexity and cost.
As is well known for proton-exchange-membrane fuel cells, purging the fuel
path
through the fuel cells is effective in returning the electrochemical reaction
to full capacity.
The purged fuel is typically vented from the fuel exhaust stream to the
environment;
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CA 02523640 2005-10-18
however, due to the danger of creating a flammable mixture of fuel and air in
the presence
of a potential source of ignition, the purged fuel is diluted to below the
lower flammability
limit of the fuel before being exposed to a potential source of ignition, such
as may be
present in the environment. This dilution of purged fuel is typically effected
by providing a
fuel dilution system and method, such as a system that includes a fan, and a
method that
includes activation of the fan. Drawbacks of providing a fuel dilution system
and method
include the requirement of additional space, increased complexity for the fuel
cell stack, and
the potential danger of creating a flammable fuel and air mixture in the event
that the fuel
dilution system and method fails.
US patent application 2004/062975 to Yamamoto et al., provides an apparatus
for
dilution of discharged fuel of a fuel cell, which has an inlet for guiding
purged hydrogen gas
coming from the fuel cell, a reservoir for storing the purged hydrogen gas
guided through the
inlet, and a cathode exhaust gas pipe penetrating the reservoir. The cathode
exhaust gas
pipe has a feature that it has holes inside the reservoir and is supplied with
cathode exhaust
gas of the fuel cell. Also the apparatus has a feature that the cathode
exhaust gas pipe
sucks the purged hydrogen gas stored in the reservoir through the holes and
discharges the
purged hydrogen gas diluted by mixing with the cathode exhaust gas. The
product
described in this patent application disadvantageously requires the need for a
dedicated
system for the dilution of discharged fuel, the need for a dedicated reservoir
for storing
purged hydrogen, the need for additional piping dedicated for cathode exhaust
and for
purged hydrogen, and the need for additional piping dedicated to the combined
cathode
exhaust and purged hydrogen.
SUMMARY OF THE INVENTION
A fluid management system for a fuel cell stack, the fluid management system
comprising a) a humidifier comprising fuel and oxidant supply conduits each
having a water
permeable separator membrane, and fuel and oxidant exhaust conduits, wherein
at least
one of the exhaust conduits is in fluid communication with the separator
membrane of at
least one of the supply conduits and comprises a first liquid water separator
that coalesces
liquid water from an exhaust stream flowing through the exhaust conduit; and
b) a manifold
for fluidly coupling the humidifier and heat exchanger supply and exhaust
conduits to
corresponding supply and exhaust conduits of a fuel cell stack.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an isometric view of a fluid management system according to one
embodiment of
the invention connected to a fuel cell stack.
Fig. 2 is an isometric view of a fluid management system according to one
embodiment of
the invention.
Fig. 3 is an isometric view of a fluid management system according to one
embodiment of
the invention with an insulating jacket removed.
Fig. 4 is an isometric view of a fluid management system according to one
embodiment of
the invention with the insulating jacket and tension bands removed.
Fig. 5 is a side view of a fluid management system according to one embodiment
of the
invention.
Fig. 6 is a bottom view of a fluid management system according to one
embodiment of the
invention.
Fig. 7 is a cross-sectional view of humidifier assemblies of a fluid
management system
according to one embodiment of the invention.
Fig. 8 is an exploded isometric view of a fluid management system according to
one
embodiment of the invention.
Fig. 9 is an exploded isometric view of a fluid management system according to
one
embodiment of the invention showing a fuel flow path.
Fig. 10 is an exploded isometric view of a fluid management system according
to one
embodiment of the invention showing a fresh air flow path.
Fig. 11 is an exploded isometric view of a fluid management system according
to one
embodiment of the invention showing an exhaust humidified flow path.
Fig. 12 is an exploded isometric view of a fluid management system according
to one
embodiment of the invention showing a coolant flow path.
Fig. 13 is a side view of a fuel purge valve of a fluid management system
according to one
embodiment of the invention.
Fig. 14 is a flow chart showing a first method of operating the present
invention.
Fig. 15 is a flow chart showing a second method of operating the present
invention.
Fig. 16 is a schematic representation of the fluid management system according
to one
embodiment of the invention showing fluid flows.
Fig. 17 is a schematic representation of the fluid management system according
to one
embodiment of the invention showing fluid flows.
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DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
In the .following description, the coalescing of water refers to the uniting
of liquid
water droplets into larger liquid water drops. The condensing of water refers
to the change
of water vapor into liquid water. The terms pervaporation and permeation are
used
S interchangeably.
According to one embodiment of the invention and referring to Fig. 1, a fluid
management system 10 is close coupled to a fuel cell stack 50, and serves to
transfer heat
and water vapor from reactant gas exhausts to reactant gas supplies; removes
liquid water
from the reactant gas exhausts; and transfers heat from the fuel cell stack 50
to gas
supplies within the fluid management system 10 by way of a coolant circuit for
the purpose
of maintaining the gas supplies at their dewpoint temperature. In a preferred
embodiment
the fluid management system 10 is shaped to close couple to a Ballard Power
Systems
Model Mk902 fuel cell stack, which is depicted as fuel cell stack 50 formed as
an elongate
fuel cell stack with fluid inlets and outlets at opposing ends. In an
alternate embodiment, the
fluid management system 10 is shaped to close couple to a fuel cell stack of
another design.
Specifically in one alternate embodiment, a fuel cell stack may have all the
fluid ports at one
region of the fuel cell stack. In another embodiment of the present invention,
the fluid
management system is shaped to have a minimum size, and a fuel cell stack is
shaped to
close couple to the fluid management system.
Fig. 2 shows the fluid management system 10 showing a first manifold 20, a
first
manifold cover 21, a second manifold 22, a second manifold cover 23, fuel cell
stack
fasteners 9, stack supports 15, and an insulating jacket 11. The insulating
jacket 11 protects
and insulates the components contained therein. In an alternate embodiment of
the present
invention, the insulating jacket covers the entire fluid management system.
Close coupling
of the fluid management system 10 to a fuel cell stack 50 is achieved by
conforming the
shape of the fluid management system 10 to the fuel cell stack 50, and
directly coupling the
manifolds 20, 22 to the manifolds of the fuel cell stack 50, thereby avoiding
the need for
connecting apparati such as pipes and tubes.
Fig. 5 is a side view and Fig. 6 is a bottom view of the embodiment of the
invention
shown in Fig. 2.
Fig. 3 shows the fluid management system 10 without the insulating jacket 11,
showing a first tension band 13 and a second tension band 14. The first
tension band 13
fastens a fuel humidification assembly 17 to the first and second manifolds
20, 22. The
second tension band 14 fastens an oxidant humidification assembly 18 to the
first and
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second manifolds 20, 22. The first tension band 13 is held away from the fuel
humidification
assembly 17 by a first tension band pad 13a. The second tension band 14 is
held away from
the oxidant humidification assembly 18 by a second tension band pad 14a.
Fig. 4 shows the fluid management system 10 without the insulating jacket and
without tension bands and without first and second tension bad pads, and
showing a first
temperature control jacket 12a of the fuel humidification assembly 17 and a
second
temperature control jacket 12b of the oxidant humidification assembly 18.
In the preferred embodiment of the invention, the fluid management system 10
comprises two manifolds 20, 22 coupled to two humidification assemblies 17,
18. In an
alternate embodiment of the present invention, one manifold performs the
functions of the
two described manifolds of the preferred embodiment by arranging all the fluid
flow paths to
traverse one manifold. In a further alternate embodiment of the present
invention, one
humidification assembly performs the functions of the two described
humidification
assemblies of the preferred embodiment by arranging one humidification
assembly inside
the other humidification assembly.
In the preferred embodiment of the invention, each humidification assembly 17,
18 is
largely tubular in shape, and various chambers and passages are formed largely
as a series
of concentric largely tubular chambers, one inside the other, while some
passages are
orifices that allows fluids to pass from one largely tubular chamber to an
adjacent largely
tubular chamber. In an alternate embodiment of the present invention, each
humidification
assembly is largely rectangular in shape, and various compartments and
passages are
formed partly as a series of plates, one plate beside the adjoining plate, one
plate surface
coupled to the adjoining plate surface.
Fig. 8 shows an exploded isometric view according to one embodiment of the
fluid
management system 10 without the insulating jacket 11, and without the tension
bands 13,
14, and without first and second tension bad pads 13a, 14a. A first access
gallery 16 is
provided for assembly and maintenance to the first manifold 20. A second
access gallery
(not shown) is provided for assembly and maintenance to the second manifold
22.
Figs. 9 and 16 show the path that a fuel supply stream takes traversing the
fluid
management system 10 in the preferred embodiment of the invention. The fuel
supply for
fuel cell stack 50 comes from a fuel source 19. The fuel supply stream enters
the fluid
management system 10 through a fuel supply inlet port 53 and a fuel supply
inlet 52 into the
first manifold 20. The fuel source 19 contains a pressurized gaseous fuel. The
pressure of
the gaseous fuel provides sufficient force to transfer the fuel supply stream
through the fluid
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management system 10 to the fuel cell stack 50 and back to the fluid
management system
whenever a path to the fluid management system is opened.
Fuel sources 19 are well understood with respect to fuel cells, and may
comprise a
plurality of components, including a pressure vessel, a pressure vessel
shutoff valve
5 assembly, a motor operated supply valve, a check valve, a pressure relief
valve, pipes,
tubes and couplings (none shown). The pressure vessel holds a pressurized
gaseous fuel,
when operational. The path from the fuel source 19 to a fluid management
system and a
fuel cell stack is opened and the fuel starts to flow when a supply valve (not
shown) is
opened. The supply valve opens and closes in response to signals from a fuel
cell system
10 controller (not shown), and may be partially open.
With reference to Fig. 7, the fuel supply stream passes from the first
manifold 20 into
the inside of a first membrane tube bundle 30 arranged longitudinally within a
fuel
humidification chamber 73 inside a fuel humidification shell 24 of the fuel
humidification
assembly 17. The fuel supply stream is humidified within the first membrane
tube bundle 30
by the pervaporation of water vapor from an oxidant exhaust stream within the
fuel
humidification chamber 73 into the membrane tubes of the first membrane tube
bundle 30.
The path of the oxidant exhaust stream through the fluid management system
will be
described.
The humidified fuel supply stream leaves the fuel humidification assembly 17
and
enters the second manifold 22. From the second manifold 22, the humidified
fuel supply
stream transfers to a humidified fuel supply port 54 where it leaves the fluid
management
system 10 and enters the fuel cell stack 50 for consumption in the
electrochemical reaction
to generate electricity.
Some of the fuel supply stream is consumed in the fuel cell stack 50 to
generate
electricity. The unconsumed fuel ("fuel exhaust") stream from the fuel cell
stack 50 enters
the fluid management system 10 through a fuel exhaust port 56 into the first
manifold 20.
From the first manifold 20, the fuel exhaust stream passes through a fuel
transfer line 57 to
a fuel exhaust passage 57a within the second manifold 22. Within the fuel
exhaust passage,
the fuel exhaust stream passes through a first water coalescing separator 40,
which
contains a first water coalescing medium 41, that coalesces liquid water from
the fuel
exhaust stream and allows the liquid water to fall under gravity to the bottom
of the fuel
exhaust passage 57a where the liquid water accumulates.
In the preferred embodiment of the invention, the fuel water coalescing medium
41 is
a polyester mesh distributed by the company Merryweather Foam under the brand
and
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number Regicell 10, however, other similar meshes may be used instead without
detracting
from the invention.
The fuel exhaust stream leaves the coalescing separator 40 and leaves the
fluid
management system 10 by way of a fuel recirculation outlet 58 and a fuel
recirculation outlet
port 58a to a fuel recirculation pump 108. From the fuel recirculation pump
108, the fuel
exhaust stream re-enters the fluid management system 10 through a fuel
recirculation inlet
port 59a and a fuel recirculation inlet 59 into the second manifold 22 and
blends with the
humidified fuel stream upstream of the humidified fuel supply port 54.
Blending of the two
fuel streams is accomplished by the simple joining of the passages that carry
the humidified
fuel supply stream and the fuel exhaust stream. The blending rate is
controlled by design
through the relative sizing of the respective two input passages and the one
output passage.
The fuel recirculation pump 108 adds sufficient force to the fuel exhaust
stream to transfer
the fuel stream through the fluid management system 10 to the fuel cell stack
50 and back
to the fluid management system 10.
Fuel recirculation pumps 108 are well understood with respect to fuel cells,
and may
comprise a plurality of components, including a circulation pump, a pump
motor, a flow
sensor, a pressure sensor, a fuel filter, pipes, tubes, couplings and a power
source for those
components that require power to operate (none shown). In an alternate
embodiment of the
present invention, the fuel recirculation pump 108 is integrated with the
fluid management
system 10 within a single housing.
In the preferred embodiment of the invention, a fuel purge valve 34 is
provided on
the fluid management system 10 to actively effect the venting of fuel purged
from the fuel
cell stack 50 and to simultaneously passively effect the draining of
accumulated liquid water
from the bottom of the fuel exhaust passage 57a. The purged fuel and
accumulated liquid
water is directed to the second oxidant exhaust stream within the second
manifold 22 by the
opening of the fuel purge valve 34. With reference to Fig. 13, the fuel purge
valve 34
consists of an actuation portion 34a and a flow directing portion 34b. At
least the flow
directing portion 34b is located within the fuel exhaust passage 57a of the
second manifold
22 and, when open, creates a passage from the fuel exhaust stream to the
second oxidant
exhaust stream just upstream of a first oxidant exhaust outlet 67. The purged
fuel and
accumulated liquid water combines with the second oxidant exhaust stream and
flow
through the first oxidant exhaust outlet 67 and a first oxidant exhaust outlet
port 68 to the
environment.
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The fuel purge valve 34 is opened and closed by way of signals from a fuel
cell
system controller (not shown) that are transmitted to the fuel purge valve by
way of fuel
purge valve electrical signal connectors 34c. A fuel cell system controller
may automatically
open and close the purge valve 34 at a regular time interval or in response to
voltage
signals from the fuel cell stack 50, or as a combination of time interval and
voltage signals.
In the preferred embodiment of the invention, the fuel purge valve 34 is a
shutoff
valve distributed by the company Components For Automation under the part
number 538,
and adapted to fit the preferred embodiment of the invention, but may be
another shutoff
valve without detracting from the invention.
Figs. 10 and 16 show the path that an oxidant supply stream takes traversing
the
fluid management system 10 in the preferred embodiment of the invention. The
oxidant
supply stream traverses an oxidant supply circuit 107, and enters the fluid
management
system 10 through an oxidant supply inlet port 61 and an oxidant supply inlet
60 into the
second manifold 22. With reference to Fig. 7, from the second manifold 22 the
oxidant
supply stream passes into the inside of the membrane tubes of a second
membrane tube
bundle 32 arranged longitudinally within an oxidant humidification chamber 74
inside an
oxidant humidification shell 25 of the oxidant humidification assembly 18.
The oxidant supply stream is humidified within the second membrane tube bundle
32
by the pervaporation of water vapor from the oxidant exhaust stream within the
oxidant
humidification chamber 74 into the second membrane tube bundle 32. The
humidified
oxidant supply stream leaves the second humidification assembly 18 and enters
the first
manifold 20. From the first manifold 20, the humidified oxidant supply stream
transfers to a
humidified supply oxidant port 62 where it leaves the fluid management system
10 and
enters the fuel cell stack 50 for consumption in the electrochemical reaction
to generate
electricity.
Oxidant supply circuits 107 are well understood with respect to fuel cell
power
systems, and may comprise a plurality of components, including a compressor, a
shutoff
valve assembly, a filter, a motor operated supply valve, a check valve, a
pressure relief
valve, pipes, tubes and couplings (none shown). The path from the oxidant
supply circuit
107 to the fluid management system and the fuel cell stack is opened and the
oxidant starts
to flow when a supply valve (not shown) is opened. The supply valve opens and
closes in
response to signals from a fuel cell system controller (not shown), and may be
partially
open.
CA 02523640 2005-10-18
In the preferred embodiment of the invention, the force necessary to transfer
the
oxidant supply stream through the fluid management system 10 to the fuel cell
stack 50 is
provided by an oxidant supply circuit 107 that is external to the fluid
management system. In
an alternate embodiment of the present invention, an oxidant supply circuit is
integrated with
the fluid management system 10 within a single housing.
Some of the oxidant supply is consumed in the fuel cell stack 50 to generate
electricity. Figs. 11 and 16 show the path that the unconsumed oxidant
("oxidant exhaust")
stream takes traversing the fluid management system 10. The oxidant exhaust
stream from
the fuel cell stack 50 enters the fluid management system 10 through an
oxidant exhaust
inlet 63 into the second manifold 22. With reference to Fig. 7, from the
second manifold 22
the oxidant exhaust passes into the fuel humidification assembly 17 where it
enters an
oxidant coalescing separator inlet passage 72a inside of a separator shell 37.
From the
oxidant coalescing separator inlet passage 72a, the oxidant exhaust passes
upward through
at least one oxidant water coalescing separator 44 into an oxidant coalescing
separator
outlet passage 72b. The oxidant water coalescing separator 44 comprises a
mostly vertically
elongate chamber that allows liquid water from the oxidant exhaust stream to
coalesce and
fall under gravity to the bottom of the oxidant coalescing separator inlet
passage 72a.
The oxidant water coalescing separator 44 may optionally contain a water
coalescing
medium 45. In the preferred embodiment of the invention, the optional oxidant
water
coalescing medium is a polyester mesh distributed by the company Merryweather
Foam
under the brand and number Regicell 10, however, other similar meshes may be
used
instead without detracting from the invention.
From the oxidant coalescing separator outlet passage 72b, the oxidant exhaust
splits
into a first and a second oxidant exhaust stream. The first oxidant exhaust
stream enters a
fuel humidification chamber oxidant inlet 72c, which is comprised of an
orifice through a fuel
humidification shell 24, and from there enters the fuel humidification chamber
73. The fuel
humidification chamber oxidant inlet 72c is sized to allow a predetermined
portion of the
total oxidant exhaust stream into the fuel humidification chamber 73.
Within the fuel humidification chamber 73 the first oxidant exhaust stream
flowingly
surrounds the first membrane tube bundle 30. Some of the water vapor entrained
in the
oxidant exhaust stream pervaporates into the first membrane tube bundle 30 to
humidify the
fuel supply stream within.
The second oxidant exhaust stream enters an oxidant passage outlet 72d, and
from
there passes through the first manifold 20 to the oxidant humidification
chamber 74 within
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the oxidant humidification assembly 18, where the second oxidant exhaust
stream flowingly
surrounds the second membrane tube bundle 32. Some of the water vapor
entrained in the
second oxidant exhaust stream pervaporates into the second membrane tube
bundle 32 to
humidify the oxidant supply stream within.
The first and second membrane tube bundles 30, 32 are bundles of tubes made of
the membrane sold under the brand NAFION, a polymer manufactured by the
company
DuPont, or some similar ion-conductive polymer such as a
perfluorocarbonsulfonic acid-
based ionomer. In the preferred embodiment of the invention, the membrane tube
bundles
are provided in assemblies manufactured by the company Permapure and
distributed under
the part numbers DB-125 and DB-150; however, other similar bundles of hollow
thread
water permeable membranes may be used instead without detracting from the
invention. In
an alternate embodiment of the present invention, the membrane tube bundles
20, 22 are
replaced by a single membrane tube.
In an alternate embodiment of the present invention, a single oxidant exhaust
stream
passes sequentially through the both of the fuel humidification assembly 17
and the oxidant
humidification assembly 18.
In the preferred embodiment of the invention, the second oxidant exhaust
stream
passes from the oxidant humidification chamber 74 into the second manifold 22
from where
it passes through the first oxidant exhaust outlet 67 and the first oxidant
exhaust outlet port
68 to the environment.
The first oxidant exhaust stream passes from the fuel humidification chamber
73 into
the first manifold 20, from where it passes through a second oxidant exhaust
outlet 64 and a
second oxidant exhaust outlet port 65 into an oxidant exhaust transfer line
66. The second
oxidant exhaust stream traverses the oxidant exhaust transfer line 66 to a
third oxidant
exhaust outlet 67a, where it joins the second oxidant exhaust stream upstream
of the first
oxidant exhaust outlet port 68, from where it passes through the first oxidant
exhaust outlet
port 68 to the environment.
In the preferred embodiment of the invention, the accumulated liquid water at
the
bottom of the oxidant coalescing separator inlet passage 72a is carried partly
under the
force of gravity and partly from the pressure of the second oxidant exhaust
stream to the
oxidant passage outlet 72d (shown on Fig. 7) on the first manifold 20 and
continues with the
second oxidant exhaust stream on its path to the environment.
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In an alternate embodiment of the present invention, the accumulated liquid
water is
directed from the first manifold 20 to a water drain 42 and a water drain port
43 to the
environment.
The source of water for the fluid management system 10 is the water produced
by
the electrochemical reaction between hydrogen and oxygen within a fuel cell,
commonly
referred to as product water. Product water accumulates primarily on the
oxidant side of a
PEM fuel cell, and is removed from the fuel cell by the flow of the oxidant
exhaust. Product
water takes the form of partly liquid water and partly water vapor. In the
preferred
embodiment of the invention, the liquid water is coalesced, separated and
removed within
the fluid management system 10 and the water vapor is retained in the fuel
exhaust and in
the oxidant exhaust, and the water exhaust in the oxidant exhaust is at least
in part,
transferred to the gas supplies. As the oxidant exhaust contains water vapor
from the
product water, the water vapor is available for the humidification of the fuel
supply and the
oxidant supply.
During operation of a fuel cell stack 50, the water vapor entrained in the gas
supplies
is not consumed. Fuel is partly consumed during operation of the fuel cell;
therefore the
water vapor entrained in the fuel supply stream is concentrated in the fuel
exhaust stream,
leading to condensation of some of the water vapor to liquid water. The fuel
exhaust stream
is therefore saturated and contains liquid water, and can be recirculated to
the fuel cell stack
50 without additional humidification. The liquid water in the fuel exhaust
stream is
advantageously removed in the preferred embodiment of the present invention in
order to
protect the fuel circulation pump 108 from damage.
The oxygen in the oxidant supply stream is partly consumed during operation of
the
fuel cell stack 50; therefore the water vapor entrained in the oxidant supply
stream is
concentrated in the oxidant exhaust stream, leading to condensation of some of
the water
vapor to liquid water. Additionally, the consumed fuel and oxidant combine on
the oxidant
side of the PEM fuel cell membranes to produce product water, as noted above.
The oxidant
exhaust stream is therefore saturated and contains liquid water. The water
vapor in the
oxidant exhaust stream is advantageously transferred to the fuel supply stream
and to the
oxidant supply stream by pervaporation through the first and second membrane
tube
bundles 30, 32 respectively. The liquid water in the oxidant exhaust stream is
advantageously removed in the preferred embodiment of the present invention in
order to
prevent clogging of the membrane tube bundles 30, 32.
13
CA 02523640 2005-10-18
An objective of the fluid management system is humidification of fuel cell
supply
gases to as close to saturation as possible without allowing the condensation
of water vapor
to liquid water. As the saturation level of water vapor in a gas is relative
to the gas
temperature, near saturation is accomplished by setting a target temperature
for the gas
S supply that is slightly below, for example 2 °C below, the dewpoint
temperature of the gas
supply. As the dewpoint of the gas supply varies with the temperature of the
gas supply, the
selection of the gas dewpoint as the controlling parameter ensures that near
saturation is
achieved at all fuel cell operating temperatures.
The fuel cell operating temperature is measured in the preferred embodiment of
the
invention by sensing the fuel cell coolant temperature at the fuel cell stack
coolant inlet, and
the measurement is communicated to a fuel cell system controller, which in
turn controls
changes to one or both of the coolant flow rate and coolant temperature
accordingly within a
coolant heat rejection circuit 109.
Fuel cells are well known to generate heat while operating. Fuel cell stacks
are well
known to incorporate a coolant system for the heat management of the fuel cell
stack. Heat
is commonly rejected from the coolant stream in a coolant heat rejection
circuit as required
by the fuel cell stack under the control of a fuel cell system controller.
In the preferred embodiment of the invention, a purpose of circulating a
coolant from
the fuel cell stack 50 to the fluid management system 10 is to maintain the
fuel cell stack 50
and the fluid management system 10 at as near the same temperature as
practicable. A
purpose of close coupling the fuel cell stack 50 to the fluid management
system 10 is to
maintain the fuel cell stack 50 and the fluid management system 10 at as near
the same
temperature as possible. By maintaining the fuel cell stack 50 and the fluid
management
system 10 at as near the same temperature as practicable, the condensation of
water in the
gas supplies and gas exhausts within the fluid management system 10 is largely
prevented,
and the dewpoint temperature of the gas supplies is maintained at as high a
temperature as
practicable. By maintaining the dewpoint temperature as high as practicable,
water vapor
content of the supply gases can be maintained as close to saturation as
practicable. By
maintaining the water vapor content of the supply gases as close to saturation
as '
practicable, the effectiveness of the fuel cell stack's power generation
capability is
enhanced.
The temperature of a fuel cell stack 50 is close to ambient when the fuel cell
stack 50
is not operating. In the preferred embodiment of the invention, upon start-up
of the fuel cell
stack 50 and the fluid management system 10, the temperature of the fuel cell
stack 50 rises
14
CA 02523640 2005-10-18
in response to the heat regenerated in the electrochemical reaction of the
fuel cell stack 50.
During start-up of the fuel cell stack 50, and the fluid management system 10,
the fuel cell
gas supplies are humidified in the fluid management system 10 to near
saturation very
quickly, as the amount of input water vapor that is required for near
saturation humidification
of the supply gases is small, and is adequately supplied by the fuel cell
stack's product
water and carried to the fluid management system 10 by the oxidant exhaust
stream. During
the warm-up period between start-up and full-temperature operation of the fuel
cell stack 50
and the fluid management system 10, in which the fuel cell operating
temperature rises from
near ambient temperature to full operating temperature, the near saturation of
the supply
gases is maintained by the simultaneous increase in the amount of source water
vapor from
the fuel cell stack's product water produced by the fuel cell stack 50 and
carried by the
oxidant exhaust stream to the fluid management system 10.
In the preferred embodiment of the invention, the temperature of the supply
gases is
maintained at near the temperature of the fuel cell stack 50 by the close
coupling of the fluid
management system 10 to the fuel cell stack 50, and by control of the flow
rate and
temperature of the coolant stream that passes between the fuel cell stack 50
and the fluid
management system 10.
Figs. 12 and 17 show the path that a coolant stream takes traversing the fluid
management system 10 and the fuel cell stack 50 in the preferred embodiment of
the
invention. From a coolant heat rejection circuit 109, the coolant stream
enters the fluid
management system 10 through a coolant inlet port 91 and a coolant inlet 90
into the first
manifold 20, from where it leaves the fluid management system 10 through a
coolant supply
port 94 to the fuel cell stack 50, where it absorbs heat from the fuel cell
stack 50 during fuel
cell operation.
In an alternate embodiment of the present invention, the coolant stream passes
from
the coolant heat rejection circuit 109 to the fuel cell stack 50 without
passing through the
fluid management system 10.
In the preferred embodiment of the invention, the coolant stream from the fuel
cell
stack 50 enters the fluid management system 10 through a coolant return port
95 into the
second manifold 22 where it splits into a first and a second coolant stream.
The first coolant
stream passes from the second manifold 22 into a first coolant passage 100
(shown in Figs.
7 and 17) inside of the first temperature control jacket 12a of the fuel
humidification
assembly 17. The coolant transfers heat conductively through the separator
shell 37 to the
oxidant exhaust stream therein. The path of the first and second oxidant
exhaust streams
CA 02523640 2005-10-18
from within the separator shell 37 to within the fuel humidification chamber
73 and to within
the oxidant humidification chamber 74 was described. The first oxidant exhaust
stream
carries the entrained heat to within the fuel humidification chamber 73 and
transfers heat
conductively and convectively through the first membrane tube bundle 30 to the
supply fuel
within. The second oxidant exhaust stream carries the entrained heat to within
the oxidant
humidification chamber 74 and transfers heat conductively and convectively
through the
second membrane tube bundle 32 to the supply oxidant within.
The second coolant stream passes from the second manifold 22 into a second
coolant passage 102 (shown in Figs. 7 and 17) inside of the second temperature
control
jacket 12b of the oxidant humidification assembly 18. The coolant transfers
heat
conductively through the oxidant humidification shell 25 to the second oxidant
exhaust
stream within the oxidant humidification chamber 74. A function of the second
coolant
stream is to ensure that the temperature of the second oxidant exhaust stream
is maintained
at as near the same temperature as the first oxidant exhaust stream as
practicable.
The first coolant stream and the second coolant stream join within the first
manifold
20, and the combined coolant stream leaves the fluid management system 10
through a
coolant outlet 92 and a coolant outlet port 93 to the coolant heat rejection
circuit 109.
In an alternate embodiment of the present invention, the fluid management
system
10 includes only a first coolant stream.
In an alternate embodiment of the present invention, the coolant passes
through only
one of the fuel humidification assembly 17 and the air humidification assembly
18.
Coolant heat rejection circuits are well understood with respect to fuel cell
power
systems, and may comprise a plurality of components, including a coolant
reservoir,
reservoir level switches, temperature sensor, flow sensor, radiator, radiator
fan, valves,
pipes, tubes, couplings and power sources for those components that require
power to
operate (none shown). The flow of coolant through the coolant heat rejection
circuit is
controlled in response to signals from a fuel cell system controller, and may
be partially
open. The temperature of coolant through the coolant heat rejection circuit is
controlled in
response to signals from a fuel cell system controller. In the preferred
embodiment of the
invention, the coolant is water, but in an alternate embodiment of the present
invention the
coolant is a glycol solution. In an alternate embodiment of the present
invention, the coolant
heat rejection circuit 109 is integrated with the fluid management system 10
within a single
housing.
16
CA 02523640 2005-10-18
In the preferred embodiment of the invention, coolant can be bled from the
fluid
management system 10 by way of a coolant bleed port 36, when coolant removal
is required
for maintenance of the fluid management system 10 or of the fuel cell stack
50.
With reference to Figs. 12 and 14, a coolant inlet temperature transducer 112
in the
first manifold 20 and a coolant outlet temperature transducer 110 in the
second manifold 22
measure the temperature of the coolant at their respective locations in Step
120 of Fig. 14.
The temperature data from transducers 112, 110 is transferred electronically
to a fuel cell
system controller (not shown) in Step 121. In Step 122, the fuel cell system
controller
compares the measured temperatures against a predetermined range of
operational
temperatures, and when a measured temperature is different from the
predetermined range
of said operational temperatures, the fuel cell system controller in Step 123
signals the
coolant circulation circuit to increase or decrease the coolant temperature
accordingly. The
coolant circulation circuit may increase or decrease the coolant temperature
through a
variety of methods well known in the art, such as direct a portion of the
coolant stream
through a radiator included in the coolant circulation circuit 109.
Additionally, in Step 124 the fuel cell system controller subtracts the
temperature
reading from the coolant inlet temperature transducer 112 from the temperature
reading of
the coolant outlet temperature transducer 110 to determine the temperature
differential of
the coolant between the locations of the two transducers 112, 110. In Step
125, the fuel cell
system controller compares the temperature differential determined in Step 124
against a
predetermined range of operational temperature differentials. When the
measured
temperature differential is different from the predetermined range of said
operational
temperature differentials, the fuel cell system controller signals the coolant
circulation circuit
to increase or decrease the flow of the coolant stream in Step 126. The
coolant circulation
circuit may increase or decrease the flow of the coolant stream through a
variety of
methods, well known in the art, such as increase or decrease the speed of a
pump included
in the coolant heat rejection circuit 109.
In the preferred embodiment of the invention, the coolant outlet temperature
transducer 110 and the coolant inlet temperature transducer 112 are
temperature
transducers distributed by the Ford Motor Company under the part number F6AZ-
9F951-AA,
but may be other temperature transducers without detracting from the
invention.
In the preferred embodiment of the invention, an oxidant temperature
transducer 114
in the second manifold 22 measures the temperature of the oxidant exhaust. The
temperature data from the oxidant temperature transducer 114 is transferred
electronically
17
CA 02523640 2005-10-18
to a fuel cell system controller (not shown). The fuel cell system controller
uses the oxidant
exhaust temperature data to create high-temperature warnings and alarms for
the fuel cell
stack 50. In the preferred embodiment of the invention, the oxidant
temperature transducer
114 is a temperature transducer distributed by the Ford Motor Company under
the part
number F6AZ-9F951-AA, but may be another temperature transducer without
detracting
from the invention.
With reference to Fig. 15, a fuel cell system controller (not shown) receives
a signal
from a fuel cell transducer in Step 130, or from a timer that times fuel cell
operation in Step
130a. The fuel cell system controller compares the signals against a
predetermined set of
operational parameters and fuel cell operation times in Step 131. When the
received signal
is different from the predetermined range of said operational parameters, or
the time has
exceeded a fuel cell operation time, the fuel cell system controller signals
the fuel purge
valve 34 to open for a predetermined length of time in Step 132.
In the preferred embodiment of the invention, the fuel is gaseous hydrogen. In
alternate embodiments of the present invention, the fuel may be another
gaseous fuel such
as methane, propane, butane, vaporized methanol, vaporized ethanol, vaporized
gasoline,
vaporized hydrogen peroxide, or another gaseous fuel, or any combination
thereof.
Furthermore, the gaseous fuel may be reformate, which is mostly hydrogen mixed
with other
fuels, and is created when a hydrocarbon fuel such as natural gas is reformed.
In the preferred embodiment of the invention, the oxidant is air. In alternate
embodiments of the present invention, the oxidant is oxygen, or a gas
containing a
significant portion of oxygen, for example, 20% oxygen.
It is to be understood that even though various embodiments and advantages of
the
present invention have been set forth in the foregoing description, the above
disclosure is
illustrative only, and changes may be made in detail, and yet remain within
the broad
principles of the invention. Therefore, the present invention is to be limited
only by the
claims appended to the patent.
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