Fuel cell system with load management

Details Fuel cell system with load management Fuel cell system with load management

2001-03-22

2004-12-28

Barr, Michael (Department: 1746)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C429S010000, C429S006000, C429S010000, C700S019000, C700S020000, C700S022000, C700S025000

Reexamination Certificate

active

06835481

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to energy-production systems, and more particularly to fuel cell systems that include a plurality of fuel cell stacks.
BACKGROUND OF THE INVENTION
Fuel cell systems include a fuel processor and a fuel cell stack. The fuel cell stack produces an electric current from the product stream of the fuel processor. For example, the fuel processor may produce hydrogen gas or hydrogen-rich gas from common feed stocks, such as water, a carbon-containing feedstock, or both. The fuel cell stack produces an electric current from the hydrogen gas.
An example of a conventional fuel cell system is shown in FIG.
1
and indicated generally at
10
. System
10
includes a fuel processing assembly
11
and a fuel cell stack
22
. Fuel processing assembly
11
includes a suitable fuel processor
12
and a feed stream delivery system
17
, which delivers a feed stream
16
to the fuel processor. Fuel processor
12
is adapted to produce a product hydrogen stream
14
containing hydrogen gas from feed stream
16
, which contains the feedstock for the fuel processor.
The composition and number of individual streams forming feed stream
16
will tend to vary depending on the mechanism by which fuel processor
12
is adapted to produce product hydrogen stream
14
. For example, if fuel processor
12
produces stream
14
by steam or autothermal reforming, feed stream
16
contains a carbon-containing feedstock
18
and water
20
. If fuel processor
12
produces stream
14
by pyrrolysis or catalytic partial oxidation of a carbon-containing feedstock, feed stream
16
contains a carbon-containing feedstock and does not include water. If fuel processor
12
produces stream
14
by electrolysis, feed stream
16
contains water and does not contain a carbon-containing feedstock. Examples of carbon-containing feedstocks include alcohols and hydrocarbons. When the feed stream contains water and a carbon-containing feedstock that is soluble with water, the feed stream may be a single stream, such as shown in FIG.
1
. When the carbon-containing feedstock is not miscible in water, the water and carbon-containing feedstock are delivered in separate feed streams, such as shown in FIG.
2
.
Fuel cell stack
22
is adapted to produce an electric current from the portion of product hydrogen stream
14
delivered thereto. Fuel cell stack
22
includes a plurality of fuel cells
24
integrated together between common end plates
23
, which contain fluid delivery/removal conduits (not shown). Examples of conventional fuel cells include proton exchange membrane (PEM) fuel cells and alkaline fuel cells. Fuel cell stack
22
may receive all of product hydrogen stream
14
. Some or all of stream
14
may additionally, or alternatively, be delivered, via a suitable conduit, for use in another hydrogen-consuming process, burned for fuel or heat, or stored for later use.
Fuel cell stack
22
receives at least a substantial portion of product hydrogen stream
14
and produces an electric current
26
therefrom. This current can be used to provide electrical power to an associated energy-consuming device
28
, such as a vehicle or a house or other residential or commercial dwelling.
In
FIG. 3
, an illustrative example of a fuel cell stack is shown. Stack
22
(and the individual fuel cells
24
contained therein) includes an anode region
32
and a cathode region
34
, which are separated by an electrolytic membrane or barrier
36
through which hydrogen ions may pass. The regions respectively include anode and cathode electrodes
38
and
40
. The anode region
32
of the fuel cell stack receives at least a portion of product hydrogen stream
14
. Anode region
32
is periodically purged, and releases a purge stream
48
, which may contain hydrogen gas. Alternatively, hydrogen gas may be continuously vented from the anode region of the fuel cell stack and re-circulated. The purge streams may be vented to the atmosphere, combusted, used for heating, fuel or as a feedstock for the fuel processing assembly. The purge streams from the fuel cell stacks may be integrated into a suitable collection assembly through which the combined purge stream may be used for fuel, feedstock, heating, or otherwise harvested, utilized or stored.
Cathode region
34
receives an air stream
42
, and releases a cathode air exhaust stream
44
that is partially or substantially depleted in oxygen. Air stream
42
may be delivered by an air delivery system
46
, which is schematically illustrated in FIG.
3
and may take any suitable form, such as a fan, blower or the like. Electrons liberated from the hydrogen gas cannot pass through barrier
36
, and instead must pass through an external circuit
49
, thereby producing electric current
26
that may be used to meet the load applied by device
28
. Current
26
may also be used to power the operation of the fuel cell system. The power requirements of the fuel cell system are collectively referred to as the balance of plant requirements of the fuel cell system.
Because fuel cell system
10
relies upon a single fuel cell stack and a single fuel processor, it suffers from some limitations due to its reliance on those components. For example, if stack
22
requires maintenance, is damaged or otherwise needs to be removed from service, system
10
is unable to provide power to device
28
, other than previously stored power, if any. Similarly, if fuel processor
12
requires maintenance, is damaged or otherwise needs to be removed from service, system
10
is unable to provide feedstock, such as product hydrogen stream
14
, to fuel cell stack
22
, other than previously stored feedstock, if any.
SUMMARY OF THE INVENTION
The present invention is directed to a fuel cell system having a redundancy of at least one operational component, such as a redundancy of fuel cell stacks and/or a redundancy of fuel processors. In some embodiments, the fuel cell system may include a plurality of fuel cell stacks adapted to provide partial and/or total redundancy. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks adapted to deliver the same maximum rated power output of a comparative fuel cell system having only a single fuel cell stack, thereby providing partial redundancy. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks adapted to deliver more than the maximum rated power output of a comparative fuel cell system having only a single fuel cell stack. In some embodiments, the fuel cell system includes a plurality of fuel cell stacks having at least n+1 (or total) redundancy compared to a fuel cell system having only a single fuel cell stack. In some embodiments, the fuel cell system includes a control system. In some embodiments, the fuel cell system may include a plurality of fuel processors to provide partial or total redundancy.


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