Fuel purging of cascaded fuel cell stack

Details Fuel purging of cascaded fuel cell stack Fuel purging of cascaded fuel cell stack

2001-08-03

2004-11-23

Crepeau, Jonathan (Department: 1746)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000

Reexamination Certificate

active

06821668

ABSTRACT:

TECHNICAL FIELD
This invention relates to rapid purging of fuel cell stack fuel flow fields and reactant manifolds, such as during startup and shutdown.
BACKGROUND ART
To achieve very high fuel utilizations, in excess of 95%, when operating a fuel cell stack on pure hydrogen, a cascade fuel flow field, illustrated in
FIG. 1
, comprises a plurality of groups
10
-
12
of fuel cells
13
arranged in flow-series relationship so that fuel from a source (not shown) passing through a fuel inlet valve
16
enters a fuel inlet manifold
17
, flows through a first group
10
of fuel cells
13
, then enters a first turn-around manifold
19
, then flows through the second group
11
of fuel cells
13
, thence through a second turn-around manifold
20
and through the third group
12
of fuel cells
13
, to an exit manifold
22
. For a typical 20 kilowatt fuel cell stack, the first group
10
has a large number of cells
13
, which may be on the order of 95 or 105 cells, the second group
11
has a lesser number of cells
13
, which may be on the order of 30-40 cells, and the third group
12
may have on the order of 5 to 15 cells. As is known, this assures that all of the cells get adequate hydrogen even with high hydrogen utilization, provided that the last group of cells
12
get adequate hydrogen.
In commonly owned, copending U.S. patent application Ser. No. 09/742,481, filed Dec. 20, 2000, now abandoned, it is shown that the more rapidly the fresh hydrogen-containing fuel flows through the anode flow field upon start-up, to displace the air therein, the quicker the hydrogen/air interface moves through the anode flow field, and the less time there is for the occurrence of corrosion of the platinum catalyst and catalyst support. In a similar fashion, it is known that the more quickly purge-air is passed through the anode upon shut-down, the less opportunity there is for hydrogen/oxygen interaction, which creates a safety hazard and may cause undesirably large voltage excursions in the cells, as described in commonly owned, copending U.S. patent application Ser. No. 09/742,497, filed Dec. 20, 2000, now abandoned.
With the cascade fuel flow field of the type described thus far with respect to
FIG. 1
, it is impossible to achieve rapid purging of the fuel flow fields since all of the purge gas must pass through a relatively small number of cells in the last cascade (the third group
12
). This problem is a large contributor to the degradation of the first cascade (group
10
) in fuel cell stacks employing cascade fuel flow fields, which in turn has impeded the adoption of the cascade design.
An alternative purge process may utilize inert gas, such as nitrogen, to purge the cell on shut-down; however, addition of an inert gas to a fuel cell system adds weight, cost and complexity which is unsuited for fuel cell powerplants used to power vehicles. Furthermore, the rapid deployment of hydrogen into the fuel flow fields upon startup, following an inert gas purge on shutdown, still remains a problem in a cascaded fuel flow field design.
DISCLOSURE OF INVENTION
Objects of the invention include: provision of a rapid purge in a fuel cell stack having cascade fuel flow fields; a fuel cell stack having the high-fuel-utilization advantage of a cascade fuel flow field without the purge problems heretofore associated therewith; an improved fuel cell stack utilizing cascade flow fields which has no unusual degradation of catalysts and other parts as a consequence of frequent shut-down and start-ups.
According to the present invention, a cascade reactant flow field of a fuel cell stack has at least one additional fuel inlet valve to provide inlet fuel directly to each cascade of the stack and at least one additional exhaust valve to remove fuel directly from each cascade of the stack.
The invention may be used not only for rapid deployment of fuel into the fuel flow field during start-up, but may also be used for a rapid purge of the fuel flow field with air during shut-down, provided the air is made available to the normal fuel inlet ports in an obvious fashion within the skill of the art.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.


REFERENCES:
patent: 5985474 (1999-11-01), Chen et al.
patent: 6251534 (2001-06-01), McElroy
patent: 6534209 (2003-03-01), Hauer

Affiliated with

Also associated with

Rating

Fuel purging of cascaded fuel cell stack does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fuel purging of cascaded fuel cell stack, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel purging of cascaded fuel cell stack will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3361097