U.S. patent application number 13/138021 was filed with the patent office on 2011-11-17 for apparatus and method for fuel cell start from freezing without melting ice.
Invention is credited to Robert M. Darling, Jonathan O'Neill, Timothy W. Patterson, JR., Michael L. Perry.
Application Number | 20110281186 13/138021 |
Document ID | / |
Family ID | 42356118 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110281186 |
Kind Code |
A1 |
Darling; Robert M. ; et
al. |
November 17, 2011 |
APPARATUS AND METHOD FOR FUEL CELL START FROM FREEZING WITHOUT
MELTING ICE
Abstract
Fuel cell systems (100, 400) and related methods involving
accumulators (106, 200, 300, 406) with multiple regions (R1, R2;
R1', R2') of differing water fill rates are provided. At least one
accumulator region with a relatively more-rapid fill rate (R2; R2')
than another accumulator region (R1; R1') is drained of water at
shutdown under freezing conditions to allow at least that region to
be free of water and ice. That region is then available to receive
water from and supply water to, a fuel cell (102; 402) nominally
upon start-up. The region having the relatively more-rapid fill
rate (R2; R2') may typically be of relatively lesser volume, and
may be positioned either relatively below or relatively above the
other region(s).
Inventors: |
Darling; Robert M.; (South
Windsor, CT) ; Patterson, JR.; Timothy W.; (West
Hartford, CT) ; Perry; Michael L.; (Glastonbury,
CT) ; O'Neill; Jonathan; (Bolton, CT) |
Family ID: |
42356118 |
Appl. No.: |
13/138021 |
Filed: |
January 26, 2009 |
PCT Filed: |
January 26, 2009 |
PCT NO: |
PCT/US2009/000514 |
371 Date: |
June 23, 2011 |
Current U.S.
Class: |
429/414 |
Current CPC
Class: |
Y02T 90/40 20130101;
H01M 8/04179 20130101; Y02E 60/50 20130101; H01M 8/04156 20130101;
H01M 2250/20 20130101; H01M 8/04303 20160201; H01M 8/04253
20130101 |
Class at
Publication: |
429/414 |
International
Class: |
H01M 8/06 20060101
H01M008/06; H01M 8/04 20060101 H01M008/04; H01M 8/24 20060101
H01M008/24 |
Claims
1. A fuel cell system (100, 400) subject to operation under
freezing conditions, comprising: at least one fuel cell (102, 402);
and an accumulator (106, 200, 300, 406) operative to receive water
from and supply water to, the at least one fuel cell, the
accumulator having structure (202, 204; 310, 312, 314, 316; 410)
defining a first region (R1, R1') having a first volume configured
to contain a volume of water during steady state operation of the
at least one fuel cell and configured to fill with water vertically
at a first rate for an arbitrary fill water flow rate, and
structure (206, 204; 310, 312, 314, 316; 414) defining a second
region (R2, R2') having a second volume and configured to fill with
water vertically at a second rate greater than said first rate for
said same arbitrary fill water flow rate, the accumulator including
a drain (121, 234, 320, 440) in the second region, said drain being
configured and operative to allow water to drain substantially
entirely from at least said second region following shutdown of the
at least one fuel cell, thereby to prevent water from freezing in
at least said second region.
2. The fuel cell system (100) of claim 1 wherein the accumulator
second region (R2) is positioned below the accumulator first region
(R1), the accumulator first region (R1) and the accumulator second
region (R2) each having respective vertical extents and having
sidewalls that define respective cross-sectional areas along the
respective vertical extents, and wherein the cross-sectional areas
of the accumulator second region are less than those of the
accumulator first region.
3. The fuel cell system (100) of claim 2 wherein the sidewalls
defining at least one of the accumulator first region (R1) and the
accumulator second region (R2) are inclined downwardly inward.
4. The fuel cell system (100; 400) of claim 1 wherein the
accumulator first region (R1) and the accumulator second region
(R2) each having respective volumes, the volume of the accumulator
first region being greater than the volume of the accumulator
second region.
5. The fuel cell system (100) of claim 1 wherein said drain in said
accumulator second region (R2) includes a valve (121; 234; 320)
that is operative to permit selective drainage of the
accumulator.
6. The fuel cell system (100) of claim 5 wherein said valve of said
drain is automatically controlled by a controller (119).
7. The fuel cell system (100; 400) of claim 1 wherein a water
conduit (126; 450, 450A) is operatively connected from at least the
accumulator second region (R2) to the at least one fuel cell to
return water to the at least one fuel cell.
8. The fuel cell system (100; 400) of claim 1 further including a
condenser (104; 404) and a variable speed condenser fan (117; 417),
said condenser fan being operative at a maximum fan speed
responsive to a start-up condition of the at least one fuel
cell.
9. The fuel cell system (100; 400) of claim 1 wherein the at least
one fuel cell comprises a stack (102; 402) of multiple Proton
Exchange Membrane fuel cells.
10. The fuel cell system (400) of claim 1 wherein the accumulator
second region (R2') is positioned above the accumulator first
region (R1'), the accumulator first region (R1') and the
accumulator second region (R2') each having respective vertical
extents and sidewalls that define respective cross-sectional areas
along the respective vertical extents, and wherein the
cross-sectional areas of the accumulator second region are less
than those of the accumulator first region.
11. The fuel cell system (100) of claim 10 wherein water from the
at least one fuel cell (402) is directed to the accumulator (406),
and the accumulator includes structure (430) to direct most of said
water from said at least one fuel cell to said accumulator second
region (R2) prior to said accumulator first region (R1').
12. The fuel cell system (100) of claim 11 wherein said drain in
said accumulator second region (R2') comprises a passive device
(440) allowing a continuous restricted flow there through to said
accumulator first region (R1').
13. The fuel cell system (100) of claim 12 wherein said passive
device comprising said drain comprises a porous plug (440).
14. The fuel cell system (100) of claim 12 wherein the structure of
said accumulator second region (R2') further includes an overflow
arrangement configured to discharge water from the accumulator
second region to the accumulator first region (R1') at a rate
greater than said continuous restricted flow via said passive
device (440) when water in said accumulator second region exceeds a
predetermined level.
15. The fuel cell system (100) of claim 10 wherein water conduits
(450, 450A) extend from each of the accumulator first region (R1')
and the accumulator second region (R2'), and are each operative to
return water to the at least one fuel cell.
16. The fuel cell system (100) of claim 10 wherein the at least one
fuel cell comprises a stack (402) of multiple Proton Exchange
Membrane fuel cells, and further including a condenser (404) and a
variable speed condenser fan (417), said condenser fan being
operative at a maximum fan speed responsive to a start-up condition
of the fuel cell stack (402).
17. A fuel cell system (100, 400) subject to operation under
freezing conditions, comprising: an accumulator (106; 200; 300;
406) operative to receive water from a fuel cell (102, 402), the
accumulator having structure (202, 204; 310, 312, 314, 316; 410)
defining a first region (R1; R1') having a first volume configured
to contain a volume of water during steady state operation of the
fuel cell and configured to fill with water vertically at a first
rate for an arbitrary fill water flow rate, and structure (206,
204; 310, 312, 314, 316; 414) defining a second region (R2; R2')
having a second volume and configured to fill with water vertically
at a second rate greater than said first rate for said same
arbitrary fill water flow rate, said first volume of said first
region (R1; R1') being greater than said second volume of said
second region (R2; R2'), and the accumulator including a drain
(121; 234; 320; 440) in the second region, said drain being
configured and operative to allow water to drain substantially
entirely from at least said second region following shutdown of the
at least one fuel cell, thereby to prevent water from freezing in
at least said second region.
18. A method of operating a fuel cell system at shutdown under
freezing conditions, the fuel cell system having a fuel cell stack,
and an accumulator for receiving water from and supplying water to
the fuel cell stack, comprising the step of: draining water from at
least a region of the of the accumulator at shutdown to allow the
region to be nominally water and ice-free during shutdown, whereby
said region of the accumulator may receive water from and supply
water to the fuel cell stack nominally upon start up.
19. The method of claim 18 including the step of providing the
accumulator with at least two regions, one of the at least two
regions filling with water vertically more rapidly than an other of
the at least two regions for the same arbitrary fill flow rate, and
wherein the step of draining at least a region of the accumulator
comprises draining at least said one more-rapidly filling
region.
20. The method of claim 19 wherein said one more-rapidly filling
region is positioned relatively above the other of the at least two
regions, and the step of draining the more-rapidly filling region
is continuous via a passive drain discharging into at least the
other of the at least two regions.
Description
BACKGROUND
[0001] The disclosure relates generally to fuel cells, and more
particularly to fuel cell systems, accumulators therefor, and
related methods. More particularly still, the disclosure relates to
such fuel cell systems and accumulators for operation in
sub-freezing temperatures.
[0002] Fuel cell systems, such as fuel cell power plants that
provide power to the propulsion system of electric vehicles, must
be operable at temperatures below that at which water will freeze.
Fuel cell systems using proton exchange membranes (PEM) are most
typically utilized in such applications, and require a
well-hydrated membrane for good operation and durability. During
normal operation, water may be drawn through a PEM fuel cell from
the anode to the cathode. Notably, water is also produced at the
cathode. Traditional methods of operating fuel cells that are shut
down in environments which may reach freezing temperatures involve
draining some or all of the water out of the fuel cell into a
reservoir of some sort, as for example an accumulator. Before
trying to establish subsequent operation, frozen water must be
melted before it can be moved back into the fuel cell, which
process may take at least several minutes, resulting in a delay
that is likely to be viewed as intolerable for such transportation
usage, where delays preferably do not exceed a few seconds.
Moreover, the melting of the frozen water typically requires the
application of a source of energy that may adversely impact the
efficiency of the system.
[0003] One approach to deal with a facet of these concerns is
described in PCT International Published Application WO 2006/112833
A1, wherein the cells include porous water transport plates, and
water contained only in the water channels, ducts or pores of cells
during operation is retained there by capillary action and/or by
vacuum during shutdown, and serves to provide some humidification
and cooling at start-up. While this may at least partly address
some problems, it relies upon the fuel cells having either coolant
ducts of small size for the capillary action or the use of a
vacuum, or both, to prevent water from "slumping" into the reactant
channels of the fuel cells. Additionally, it allows some amount of
freezing of the water within the cells themselves during shutdown,
so long as it is limited to the coolant ducts and not the reactant
channels. While this may be tolerable, it is less than desirable
because it increases the time needed to bring the cell to operating
temperature. Moreover, it does not really address the need to
relatively rapidly and efficiently provide water from a reservoir,
such as an accumulator, to the fuel cells at, or shortly after,
start-up, under freezing conditions.
SUMMARY
[0004] It has been determined that a fuel cell system with porous
water transport plates can be started, particularly though not
exclusively, under freezing conditions, if a small amount of water
can be made available to the fuel cells from the accumulator
relatively soon after starting. This is particularly true for
evaporatively cooled systems that are less dependent on large
volumes of water flow and can, therefore, be operated with less
water stored in the system. In that regard, the presently disclosed
system(s) provide an accumulator structured to assure that at least
a minimum usable quantity of water is available for supply to the
fuel cells quickly, in an acceptable interval, after start-up
occurs, even under freezing conditions. This is accomplished
without resort to supplemental thawing means, even though some
frozen water may exist in part of the accumulator.
[0005] A fuel cell system subject to operation under freezing
conditions is disclosed in which there is at least one fuel cell,
and an accumulator operative to receive water from and supply water
to, the at least one fuel cell. The water from the fuel cell may go
directly to the fuel cell, or may be delivered indirectly, as via a
condenser or the like. The accumulator has structure defining a
first region having a first volume configured to contain a volume
of water during steady state operation of the at least one fuel
cell and configured to fill with water vertically at a first rate
for an arbitrary fill water flow rate, and structure defining a
second region having a second volume and configured to fill with
water vertically at a second rate greater than said first rate for
said same arbitrary fill water flow rate. The accumulator also
includes a drain in the second region, said drain being configured
and operative to allow water to drain substantially entirely from
at least said second region following shutdown of the at least one
fuel cell, thereby to prevent water from freezing in at least said
second region. The volume of the first region is typically, though
not necessarily, greater than the volume of the second region.
[0006] In one example embodiment, the accumulator second region is
positioned lower than the accumulator first region and includes a
geometry, relative to the geometry of the first region, that fills
with water vertically more rapidly than does the first region at
the same fill water flow rate. This may be accomplished by the
walls or sides of at least the accumulator second region being
arranged to define a cross-sectional area that is generally less
than the cross sectional area defined by the walls or sides of the
accumulator first region. For example, the accumulator first region
may be defined by near-vertical or slightly inwardly inclined
walls, and the walls of the accumulator second region may extend
downward there from in and range from near vertical to inward
inclination at a relatively greater angle than for the first
region. Alternatively, the walls of both the accumulator first and
second regions may have a common inwardly inclined contour, as for
example an inverted cone, with the accumulator second region being
lower than the accumulator first region.
[0007] In another example embodiment, the accumulator second region
may be positioned or located somewhat in, and/or relatively above,
the accumulator first region, and includes a drain which allows
water to drain, preferably passively, into the larger accumulator
first region. This enables the accumulator second region to drain
out all of its water into the accumulator first region upon
shut-down, thus insuring that the second region is dry and does not
freeze. The level of water accumulated in the first region is
regulated to remain below the second region to assure the ability
of the first region to drain. The drain may be some sort of
restriction, as an orifice or porous plug. Return lines from both
of the accumulator first and second regions assure that one or both
regions may serve as sources of water for the fuel cells. The water
in the accumulator first region may be allowed to freeze upon
shutdown, since the accumulator second region goes dry and is
available to receive water quickly upon start-up. This embodiment
limits or eliminates the need to dump water from the accumulator to
prevent freeze-up.
[0008] In operation, upon shutdown of the fuel cells during
freezing conditions, water is actively or passively drained from at
least the accumulator second region to leave it dry for rapid
refilling with water upon start-up (re-start) of the fuel cells.
The active draining involves the opening and closing of a drain
valve. Assuming the restart also occurs during cold conditions,
fans associated with a condenser are set to high speed to maximize
the water returned to the accumulator first region. The fuel cells
can run sufficiently long under this cold condition for water to be
produced and collected in the accumulator second region and then
returned to the fuel cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic diagram depicting an exemplary
embodiment of a fuel cell system;
[0010] FIG. 2 is a schematic diagram depicting an exemplary
embodiment of an accumulator in accordance with FIG. 1;
[0011] FIG. 3 is a schematic diagram depicting a further exemplary
embodiment of an accumulator in accordance with FIG. 1; and
[0012] FIG. 4 is a schematic diagram depicting a further exemplary
embodiment of a fuel cell system, including accumulator.
DETAILED DESCRIPTION
[0013] Fuel cell systems and related methods involving accumulators
with regions of relatively low volume and/or relatively high
vertical fill rate are provided, several exemplary embodiments of
which will be described in detail. In this regard, in some
embodiments, sloped sidewalls of the accumulators are used. As
such, the sloped sidewalls encourage efficient draining of the
accumulators. Additionally, the low volume and/or high fill rate
regions require relatively less water to fill to a vertical height
necessary for providing the water from the accumulator. This
potentially enables water filling the low volume and/or high fill
rate region to be directed for use in other portions of a fuel cell
system more quickly.
[0014] FIG. 1 is a schematic diagram depicting an exemplary
embodiment of a fuel cell system. As shown in FIG. 1, system 100
includes a fuel cell stack 102, sometimes called a cell stack
assembly. Fuel cell stack 102 includes multiple fuel cells,
typically of the Proton Exchange Membrane (PEM) type. The fuel cell
stack is positioned above a condenser 104, which is positioned over
a water accumulator 106. An air inlet manifold 108 is located above
the fuel cell stack and an air outlet manifold 110 is positioned
below the stack. A fuel inlet manifold 120, a fuel turn manifold
122 and a fuel outlet manifold 124 also are provided.
[0015] In operation, air enters air inlet manifold 108, flows
through the oxidant flow channels of the fuel cell stack 102 to air
outlet manifold 110, and then into condenser 104. The outflow from
condenser 104 is above water line 112 of accumulator 106. Coolant
for the condenser (illustrated by arrows 114) is ambient air in
this embodiment. One or more variable-speed fans 117 are associated
with the condenser and are controlled by controller 119 to
facilitate the rate at which moisture is condensed from the air
exiting the fuel cell stack. Cool dry air from the condenser is
expelled from air outlet 116, which is located adjacent to a water
overfill 118. In some embodiments, the condenser may function as a
manifold, in which case air outlet manifold 110 may be omitted.
[0016] During operation, fuel provided to fuel inlet manifold 120
flows to the left, then through fuel turn manifold 122, after which
the fuel flows to the right. The fuel then flows out through fuel
outlet manifold 124. Also, during operation, return water from the
accumulator 106 flows through a water conduit 126 to a water
manifold 128. The water then passes into water channels within
and/or adjacent to, the various fuel cells of the fuel cell stack
102 to the top of the fuel cell stack and possibly to an upper
water manifold 130. Notably, the embodiment of FIG. 1 employs
evaporative cooling. Thus, the only water entering through the
water manifold is to replace that which is evaporated into the air
channels of the fuel cell stack. A drain/drain valve 121 is located
in the bottom of the accumulator 106, or near thereto in the return
water conduit 126, and may be controlled by controller 119 to drain
water from the system, as will be discussed further following.
[0017] The accumulator 106, in accordance with the present
disclosure, includes at least structure defining a first region
having a first volume configured to contain a volume of water
during steady state operation of the at least one fuel cell and
configured to fill with water vertically at a first rate for an
arbitrary fill water flow rate, and structure defining a second
region having a second volume and configured to fill with water
vertically at a second rate greater than said first rate for said
same arbitrary fill water flow rate. The volume of the accumulator
second region will typically be much smaller than that of the
accumulator first region, but need not be so if the water vertical
fill rate relationship expressed above is otherwise met. The
accumulator first region will be hereinafter designated R1, or a
derivative thereof, and the accumulator second region is designated
R2, or a derivative thereof. It will be noted with reference to the
embodiments of FIGS. 1-3 that there may not be a clear demarcation
of the transition from region R1 to region R2, and thus they are
depicted as overlapping. Indeed, with respect to the detailed
description of the accumulator embodiment of FIG. 2, it is
presented as having three regions, an "upper", a "lower", and an
"intermediate", but it should be understood that the intermediate
region could be viewed as all R1, all R2, or partly R1 and partly
R2, so long as the guiding requirements expressed above are
met.
[0018] FIG. 2 is a schematic diagram depicting an exemplary
embodiment of an accumulator similar to that depicted in FIG. 1. As
shown in FIG. 2, accumulator 200 includes an upper region 202, an
intermediate region 204 and a lower region 206, which collectively
comprise regions R1 and R2. Specifically, upper region 202
incorporates opposing endwalls 208, 210, and sloped sidewalls 212,
214 extending between the endwalls. Notably, lower portions (209,
211) of the endwalls define ends of the intermediate region. In the
embodiment of FIG. 2, the sidewalls are inwardly inclined
downwardly toward the intermediate region.
[0019] Intermediate region 204 is generally configured as a channel
that runs along the major central axis of the accumulator. The
intermediate region includes opposing sidewalls 220, 222, and
downwardly inclined bottom walls 224, 226, which extend toward the
lower region 206. Notably, lower portions (221, 223) of the
sidewalls 220, 222 function as sidewalls for the lower region
206.
[0020] In this regard, the lower region 206 is defined by opposing
sidewalls (lower portions of sidewalls 220, 222), endwalls 230, 232
that extend between the sidewalls, and a bottom, or drain, 234, for
connection with a drain valve and return line, such as elements 121
and 126 of FIG. 1. The lower region defines a volume that is
relatively small in comparison to the overall volume of the
accumulator. As noted previously, region R2 may consist only of
lower region 206, or it may additionally include part of
intermediate region 204.
[0021] FIG. 3 is a schematic diagram depicting an accumulator 300
that is functionally identical to that of FIG. 2, but which depicts
the range of latitude in selecting the structural configuration for
the regions R1 and R2. More specifically, whereas the accumulator
200 of FIG. 2 may have a relatively compact vertical profile, it
requires a number of planar facets to construct, the inverted
pyramidal accumulator 300 is of deeper vertical profile but relies
on fewer and simpler members or facets to construct. Indeed, the
accumulator may be as simple in shape, though not necessarily
simple to construct, as an inverted cone. Referring to FIG. 3, the
accumulator 300 is formed principally of 4 joined inverted
triangular sides 310, 312, 314, and 316, and having a small bottom,
or drain, 320 at or near its apex, for connection with a drain
valve and return line, such as elements 121 and 126 of FIG. 1.
[0022] FIG. 4 is a schematic diagram of a fuel cell system 400
generally analogous to FIG. 1, but in which the structure and
function of the accumulator 406 differ somewhat from that depicted
and described with respect to the FIGS. 1-3 embodiments. More
particularly, the fuel cell stack 402, the condenser 404, and
condenser fans 417 may be identical to those discussed with respect
to FIG. 1, and will not be described further. On the other hand,
the accumulator 406 positioned below the underside of condenser 404
is structured to comprise a relatively large container or chamber
410 having a bottom 412 for storage of the majority of water
provided by the condenser 404, and a further, typically smaller,
container or chamber 414 supported or mounted within container 410
and spaced above the bottom of container 410. The relatively large
container 410 may typically have a water level shown as 422 and
established and controlled in a known manner which may include an
overflow vent 424 for establishing a maximum water level 422 and
venting any excess water. The smaller container 414 is positioned
entirely above the level of that maximum water level established by
the overflow vent 424.
[0023] The smaller container 414 may be cup-like or bowl-like in
shape and supported from, or by, the relatively larger container
410, by inclined support baffle 430 connected to each container.
The support baffle 430 is conveniently a substantially continuous
annular surface for intercepting the majority of the water
discharged from condenser 404 and directing it into the smaller
container 414. Importantly, the general cross-sectional area of the
smaller container 414 is less, or considerably less, than that of
the relatively larger container measured at and below the typical
water level 422, such that the former will have a relatively
greater vertical fill rate than the latter for a given flow of
water. To achieve this result in view of the large cross-sectional
area of the support baffle, the smaller container 414 includes some
form of overflow vent 432 positioned to limit the effective height
of that container and thus assure the desired smaller
cross-sectional area, and to additionally provide for rapid
overflow of water to the larger container 410 if necessary.
Notably, the smaller container 414 includes at its bottom a passive
form of drain 440, which comprises a restriction such as an
orifice, a porous plug as shown, or the like.
[0024] As with the embodiments of FIGS. 1-3, the accumulator 406 of
the FIG. 4 embodiment includes a first region R1' and a second
region R2' having the same functional relationships of vertical
fill rates and possibly also volume as stated earlier, and it will
be understood that it is the relatively larger container 410 that
now constitutes the "first region" R1' (below overflow vent 424)
and the smaller container 414 constitutes the "second region" R2'
(below overflow vent 432). This is so, despite container 414 being
positioned above portions of container 410.
[0025] A water conduit 450 extends from near the bottom of
relatively larger container 410 to the water manifold 428 of the
fuel cell stack 402 to return water to the fuel cell stack. A
further water conduit 450A extends from near the bottom of the
smaller container 414 also to water manifold 428, as by connection
with conduit 450, to deliver/return water to the fuel cell stack. A
vacuum air pump 452 connected to the fuel cell stack 402 provides
the delivery/return of water to the stack from either container 410
or 414 via the conduits 450, 450A, and may be controlled by a
controller 419 which also controls the condenser fan(s) 417. These
conduits 450, 450A also allow water to drain from the stack to the
accumulator 406 on shutdown. Optional valves 460 and/or 460A may be
placed in conduits 450 and/or 450A, respectively, to avoid excess
gas ingestion.
[0026] Very general reference is made first to aspects of operation
common to all of the disclosed embodiments, and then separately to
the distinctive aspects of operation for the FIGS. 1-3 embodiments,
and then further to the distinctive aspects of the FIG. 4
embodiment. Referring to FIGS. 1-4, at the time of shutdown of the
fuel cell stack under freezing (including sub-freezing) conditions,
there will typically be accumulated condensed water in accumulator
regions R1 (or R1') and R2 (or R2'). The water in at least region
R2/R2' is either actively or passively drained to create an
ice-free region of the accumulator, and is positioned and
structured to receive new water from the condenser relatively soon
after the next start-up of the fuel cell stack. At start-up, the
controller 119, 419 causes the condenser fans 117, 417 to operate
at high speed to maximize water returned to the accumulator.
Particularly in freezing conditions, the stack can operate safely
at reduced temperature for the short interval until sufficient
water is produced. Even when ambient temperatures are relatively
warm, the stack can be started and operate effectively, premised on
relatively rapid refilling of the accumulator with water. At least
region R2/R2' is structured such that it can relatively rapidly
accumulate most or all of the new water, and it has associated with
it a return conduit 126, 450A for conveying that water back to the
fuel cell stack to cool it.
[0027] Referring specifically to the FIGS. 1-3 embodiments, the
drain valve 121 connected to the bottom of region R2 of the
accumulator is opened at shutdown, and serves to gravity-purge the
entire accumulator (regions R1 and R2) of water such that no ice is
formed in the accumulator. The valve 121 is then closed. Upon
subsequent start-up, water from the stack 102 and condenser 104 is
delivered to the accumulator 106, 200, 300 whereupon it rapidly
begins to fill region R2 for supplying the stack via return water
conduit 126. Because there was no water in the accumulator, there
is no ice that must be melted before start-up from freezing
conditions.
[0028] Referring specifically to the FIG. 4 embodiment, most or
substantially all of the water produced from condenser 404 falls to
the downwardly and inwardly inclined support baffle 430 and is
collected in the smaller container 414 comprising region R2'. That
water rapidly fills the container 414 and most simply overflows via
the overflow vent 432 and falls to the relatively larger container
410 where it accumulates as main water level 422. Concurrently, a
limited amount of the water collected in smaller container 414 also
slowly drains via the passive drain 440 to the larger container 410
below. This slow drainage via drain 440 is of little consequence
during normal steady-state operation, but is important at both a
frozen shut-down and upon a subsequent frozen start-up. More
specifically, upon a frozen shut-down, the water collected in
smaller container 414 slowly drains out of the container, to leave
it dry and ice-free. While the water accumulated below in the
relatively larger container 410 comprising region R1' is allowed to
freeze if such conditions exist, this does not prevent a subsequent
effective start-up under those conditions. Rather, at start-up,
newly condensed water from stack 402 and condenser 404 soon fills
the slow-draining smaller container 414, and water is thus
available for return to the stack via water conduit 450A.
[0029] The optional valve 460, which may be located on the water
return conduit 450 from larger container 410 prior to its junction
with the conduit 450A from smaller container 414, serves when
closed to prevent excess gas ingestion from container 410 while
thawing is occurring there. That valve should be located away from
any ice that could form. Another optional valve 460A can be located
on the water return conduit 450A from the smaller container 414 to
prevent, when closed, gas ingestion from that container, which
might otherwise occur in that short interval just after start-up
when there is still relatively little or no water in the smaller
container 414. Control of each of these valves 460, 460A may be
provided by the controller 419. Similarly, control of the vacuum
air pump 452 may be provided by the controller 419.
[0030] While certain aspects of the structure and function of the
FIG. 4 embodiment may be more complex than those of the FIGS. 1-3
embodiments, other aspects are less complex. Moreover, because the
FIG. 4 embodiment offers the ability to retain the water within the
accumulator 406 during a frozen shutdown, it minimizes or
eliminates the need to discharge liquid water overboard and may
provide relatively more water more quickly in the event of a
non-frozen/warm start-up, whether the prior shut-down was frozen or
not.
[0031] Although the disclosure has been described and illustrated
with respect to the exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made without
departing from the spirit and scope of the disclosure.
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