Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-12-15
2002-07-02
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000
Reexamination Certificate
active
06413661
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a fuel cell system and more particularly to a combustor which heats a fuel processor which produces an H
2
-rich feed gas for consumption in a fuel cell stack.
BACKGROUND OF THE INVENTION
Fuel cells have been used as a power source in many applications. For example, fuel cells have been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. PEM fuel cells include a membrane electrode assembly (MEA) comprising a thin, proton transmissive, non-electrically conductive solid polymer electrolyte membrane having the anode catalyst on one of its faces and the cathode catalyst on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings therein for distributing the fuel cells gaseous reactants over the surfaces of the respective anode and cathode catalysts. The term fuel cell is typically used to refer to either a single cell or a plurality of cells (stack) depending on the context. A plurality of individual cells are commonly bundled together to form a fuel cell stack and are commonly arranged in series. Each cell within the stack comprises the membrane electrode assembly (MEA) described earlier, and each such MEA provides its increment of voltage. A group of adjacent cells within the stack is referred to as a cluster. Typical arrangements of multiple cells in a stack are described in U.S. Pat. No. 5,763,113, assigned to General Motors Corporation.
In PEM fuel cells, hydrogen (H
2
) is the anode reactant (i.e., fuel) and oxygen is the cathode reactant (i.e., oxidant). The oxygen can be either a pure form (O
2
), or air (a mixture of O
2
and N
2
).The solid polymer electrolytes are typically made from ion exchange resins such as perfluoronated sulfonic acid. The anode/cathode typically comprises finely divided catalytic particles, which are often supported on carbon particles, and mixed with a proton conductive resin. The catalytic particles are typically costly precious metal particles. These membrane electrode assemblies are relatively expensive to manufacture and require certain conditions, including proper water management and humidification, and control of catalyst fouling constituents such as carbon monoxide (CO), for effective operation.
For vehicular applications, it is desirable to use a liquid fuel such as an alcohol (e.g., methanol or ethanol), or hydrocarbons (e.g., gasoline) as the source of hydrogen for the fuel cell. Such liquid fuels for the vehicle are easy to store onboard and there is a nationwide infrastructure for supplying liquid fuels. However, such fuels must be dissociated to release the hydrogen content thereof for fueling the fuel cell. The dissociation reaction is accomplished within a chemical fuel processor or reformer. The fuel processor contains one or more reactors wherein the fuel reacts with steam and sometimes air, to yield a reformate gas comprising primarily hydrogen and carbon dioxide. For example, in the steam methanol reformation process, methanol and water (as steam) are ideally reacted to generate hydrogen and carbon dioxide. In reality, carbon monoxide and water are also produced. In a gasoline reformation process, steam, air and gasoline are reacted in a fuel processor which contains two sections. One is primarily a partial oxidation reactor (POX) and the other is primarily a steam reformer (SR). The fuel processor produces hydrogen, carbon dioxide, carbon monoxide and water. Downstream reactors such as a water/gas shift (WGS) and preferential oxidizer (PROX) reactors are used to produce carbon dioxide (CO
2
) from carbon monoxide (CO) using oxygen from air as an oxidant. Here, control of air feed is important to selectively oxidize CO to CO
2
. A combustor typically is included in a fuel cell system and is used to heat various parts of the fuel processor, including reactors, as needed.
Fuel cell systems which process a hydrocarbon fuel to produce a hydrogen-rich reformate for consumption by PEM fuel cells are known and are described in U.S. patent application Ser. No. 08/975,422, which corresponds to U.S. Pat. No. 6,232,005 issued on May 15, 2001, in U.S. Ser. No. 08/980,087, which corresponds to U.S. Pat. No. 6,077,620 issued on Jun. 20, 2000, and in U.S. Ser. No. 09/187,125, which corresponds to U.S. Pat. No. 6,238,815 issued on May 29, 2001, each of which is assigned to General Motors Corporation, assignee of the present invention; and in International Application Publication Number WO 98/08771, published Mar. 5, 1998. A typical PEM fuel cell and its membrane electrode assembly (MEA) are described in U.S. Pat. Nos. 5,272,017 and 5,316,871, issued respectively Dec. 21, 1993 and May 31, 1994, and assigned to General Motors Corporation.
Efficient operation of a fuel cell system depends on the ability to effectively control operation of major interdependent components or subsystems such as the combustor and fuel processor. This is particularly difficult during start-up of a vehicular fuel cell system wherein the combustor heats up the fuel processor to a temperature sufficient for the fuel processor to generate hydrogen-rich feed for the fuel cell. It is also difficult to maintain combustor heat during transition from a start-up mode to a running mode where the combustor is at least partially fueled by the hydrogen-rich stream from the fuel processor.
Therefore, it is desirable to provide a method by which the fuel cell system is effectively operated during start-up and a running mode so that the combustor and fuel processor are operated efficiently.
SUMMARY OF THE INVENTION
The present invention is directed to the operation of a fuel cell system which comprises a combustor which heats a fuel processor which, in turn, generates a hydrogen-rich feed stream for use in a fuel cell stack. The hydrogen-rich feed stream is consumed in the fuel cell stack whereby electricity is produced. The present invention provides a new method for operating the combustor within the system and, particularly, an improved method for operating the combustor during start-up and transition to a running mode. In another aspect, the invention provides an improved system configuration and apparatus whereby start-up is achieved in a fuel efficient and effective manner.
In one aspect, the invention provides a method for operating a combustor to heat a fuel processor to a desired temperature during start-up in a fuel cell system. Here the term start-up indicates that the fuel processor is started from a relatively cold condition. Start-up includes commencing operation after the fuel processor was cooled down to below its desired operating temperature. The fuel processor generates a hydrogen-rich product (feed stream) from a hydrocarbon. The hydrogen-rich feed stream from the fuel processor is supplied to a fuel cell stack which generates electricity by oxidation of the hydrogen with oxygen. In a preferred start-up mode, a hydrocarbon fuel stream and an air stream are supplied to the combustor. The hydrocarbon fuel and air are reacted or burned in the combustor in order to generate heat to heat the fuel processor. The pressure of the air stream to the combustor is monitored. The products of the combustion reaction in the combustor are supplied to the fuel processor.
Preferably, the fuel processor is heated by indirect heat transfer from the products of combustion. After the products of combustion from the combustor have begun to heat the fuel processor, a hydrocarbon reactant is supplied to the fuel processor. The hydrocarbon reactant is reacted with steam, air, or a combination of both in the fuel processor. The reaction between the hydrocarbon reactant and the steam and/or air produces a hydrogen-rich feed stream which is usable in the fuel cell stack to produce electricity. Howev
Clingerman Bruce J.
Mowery Kenneth D.
Barr, Jr. Karl F.
Brooks Cary W.
Brouillette Gabrielle
Deschere Linda M.
General Motors Corporation
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