Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2000-05-05
2002-08-20
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S006000
Reexamination Certificate
active
06436561
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to electrochemical fuel cells and, more specifically, to combustors for heating a fuel processor.
BACKGROUND OF THE INVENTION
Fuel cells have been used as a power source in many applications. Fuel cells have also been proposed for use as a vehicular power plant to replace the internal combustion engine. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode side of the fuel cell and air or oxygen is supplied as the oxidant to the cathode side. PEM fuel cells include a “membrane electrode assembly” (a.k.a. MEA) comprising a thin, proton transmissive, solid polymer membrane-electrolyte having the anode on one of its faces and the cathode 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 distribution the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts. A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack.
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 fuel for the vehicle owing to the ease of on-board storage of liquid fuels and the existence of 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 heterogeneously within a chemical fuel processor, known as a fuel processor, that provides thermal energy throughout a catalyst mass and yields a reformate gas comprising primarily hydrogen and carbon dioxide. For example, in the steam and methanol reformation process, methanol and water (as steam) are ideally reacted to generate hydrogen and carbon dioxide according to this reaction:
CH
3
OH+H
2
O→CO
2
+3H
2
.
The reforming reaction is an endothermic reaction that requires external heat for the reaction to occur. The heat required to produce enough hydrogen varies with the demand put on the fuel cell system at any given point in time. Accordingly, the heating means for the fuel processor must be capable of operating over a wide range of heat outputs. Heating the fuel processor with heat generated externally from either a flame combustor or a catalytic combustor is known. U.S. patent applications Ser. No. 08/975,422 now U.S. Pat. No. 6,232,005 and Ser. No. 08/980,087 now U.S. Pat. No. 6,077,620 filed in the name of William Pettit in November, 1997, and assigned to the assignee of the present invention, disclose an improved catalytic combustor, and the integration thereof with a fuel cell system which fuels the combustor with unreformed liquid fuel, hydrogen-containing anode exhaust gas from the fuel cell, or both. The operating cycle depends on many factors, such as anode stoichiometry, steam/carbon ratio, electrical demand placed on the system, etc.
Thus, it would be desirable to provide a method for controlling a combustor in a fuel cell system which makes efficient use of all available fuel. It would also be desirable to provide a method for controlling a combustor having dual fuel and multiple fuel composition inlet streams. It would also be desirable to provide a method for controlling a combustor having dual fuel and multiple fuel composition inlet streams and dual oxidant (air) inlet streams with differing oxygen content. It would also be desirable to provide a method for controlling a combustor having dual fuel and multiple fuel composition inlet streams which meets current vehicle emission requirements at all times during the fuel cell operation cycle.
SUMMARY OF THE INVENTION
A control method for a methanol tailgas combustor used in a fuel cell system in which some unused hydrogen from the anode (anode effluent), and unused oxygen from the cathode (cathode effluent) of a fuel cell stack are supplied as separate fuel and air streams to the combustor with selective quantities of fuel processor reformate and separate fuel and air supplies. The terms effluent and exhaust are used herein interchangeably.
In one aspect of the present invention, the control method comprises the steps of:
providing first and second fuel streams to the combustor, the first fuel stream being a hydrocarbon fuel stream, the second fuel stream consisting of reformate from the fuel processor and/or the anode effluent from the fuel cell;
providing first and second air flow streams to the combustor, the first air flow stream being from first air source, the second air flow stream being the cathode effluent from the fuel cell;
determining the power input requirement of the fuel processor;
determining the output power of the combustor to support the determined power input requirement of the fuel processor; and
regulating the quantity of at least one of each of the first and second fuel streams and at least one of each of the first and second air flow streams to the combustor to provide a power output from the combustor to meet the determined power output requirement of the fuel processor.
In one aspect of the present method, the regulating step comprises the utilization of all available second fuel stream and second air flow stream in the combustor prior to supplying any of the first fuel stream and/or the first air flow stream to the combustor.
In one aspect of the present method for the initial start-up of the combustor, the method comprises the step of before supplying the first fuel stream to the combustor, preheating a catalyst bed in the combustor to a predetermined operating temperature. In the start-up mode, the first fuel stream and the first air flow stream are exclusively supplied to the combustor unless an optional buffer or supply of reformate or hydrogen is available.
In a fuel processor start-up mode of operation, the present method includes the steps of:
before supplying a hydrocarbon fuel to the fuel processor, calculating the power requirements of the combustor to raise the temperature of the fuel processor to a predetermined warm-up temperature;
determining the heat content of the first fuel stream and the first air stream to the combustor to provide the determined power requirements of the combustor to raise the fuel processor to the predetermined warm-up temperature;
measuring the temperature of the fuel processor; and
regulating the quantity of the first air stream supply to the combustor to balance the enthalpy of the first fuel stream and the first air stream supplied to the combustor to supply heat energy at the desired temperature.
Preferably, the regulating step includes the step of regulating the quantity of the first air stream supply to the combustor by controlling the output flow of one or more valves in the first air stream supply or by varying the speed of the air compression device supplying the first air flow stream. The output flow of a valve is preferably adjusted by controlling the diameter of an output flow orifice of the valve. Alternatively, the output flow of a valve is adjusted by changing the position of the valve in the valve body from open to closed or to an intermediate position such as partially open or partially closed. It is most preferred to control the diameter of the output flow orifice of the valve.
After the fuel processor has reached a predetermined warm-up temperature sufficient to produce reformate from fuel and water, the present method comprises the steps of:
diverting all of the reformate from the fuel processor to the combustor;
determining the enthalpy of the reformate generated by the fuel processor;
determining the enthalpy of the combustor output attributed to combustion of the reformate in the combustor;
calculating the power requirements of the combustor to raise the temperature of the fuel processor to a predetermined start-up temperature;
calculating the difference between the enthalpy of the reformate diverted to the c
Hart-Predmore David J.
Pettit William H.
Alejandro R.
Barr, Jr. Karl F.
Brooks Cary W.
Deschere Linda M.
General Motors Corporation
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