Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-09-28
2003-11-11
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S010000, C429S010000, C429S006000
Reexamination Certificate
active
06645652
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a hydrocarbon fueled solid polymer fuel cell system for producing electric power. More specifically, the present invention relates to a pressurized fuel cell electric power generation system that converts fuel and oxidant fluid streams into electrical energy and reaction products in a solid polymer fuel cell stack.
BACKGROUND OF THE INVENTION
Electrochemical fuel cell electric power generation systems convert fuel fluid streams, such as natural gas or propane, and oxidant fluid streams, such as oxygen or air, into respective intermediate products, such as a hydrogen-rich fuel stream and a humidified oxidant stream, which a fuel cell ultimately converts into electric power, heat, and reaction products, such as water and carbon dioxide. Fuel cell power plants are of particular interest to utilities because they can provide distributed or remote sources of electricity, thus overcoming some of the difficulties associated with conventional nuclear, coal or hydrocarbon fuel power plants, such as access to high voltage transmission lines, distribution to urban power stations, and the substantial financial commitments typically associated with installation of conventional power plants. In addition, fuel cell power generation systems are capable of operating at greater than 40% electrical efficiency, which is more efficient than combustion-based electric power plants. Fuel cell power generation systems are thus able to use readily available fuels to provide electrical power close to the point of use, quietly, with minimal emissions, and with high overall efficiency.
A hydrocarbon fueled solid polymer fuel cell electric power generation system is the subject of commonly-owned U.S. Pat. No. 5,360,679 issued Nov. 12, 1994 (“the '679 patent”) which is hereby incorporated by reference in its entirety. The '679 patent describes a fuel cell generation system that comprises:
(1) an electric power generation subsystem for producing electricity, heat, and water from a hydrogen-containing fuel stream and an oxidant stream;
(2) a fuel processing subsystem for producing a hydrogen-rich fuel for the electric power generation subsystem;
(3) an oxidant subsystem for delivering pressurized oxidant to the electric power generation subsystem;
(4) a water recovery subsystem for recovering the water produced in the electric power generation subsystem and optionally for cooling the electric power generation subsystem;
(5) a power conversion subsystem for converting the electricity produced into utility grade electricity; and
(6) a control subsystem for monitoring and controlling the supply of fuel and oxidant streams to the electric power generation subsystem.
The subsystems of the '679 patent are described with reference to
FIG. 1
, which is a schematic flow diagram of a preferred embodiment of a fuel cell power generation system disclosed in the '679 patent. The electric power generation subsystem comprises fuel cell stack
100
. Fuel cell stack
100
preferably comprises a plurality of solid polymer fuel cell assemblies. Each fuel cell assembly comprises a membrane electrode assembly interposed between two separator plates. The membrane electrode assembly typically employs an ion exchange membrane interposed between two porous, electrically conductive electrodes and a catalyst disposed at the interface between the membrane and the respective electrodes. The separator plates may comprise fluid channels for providing a flow field pattern for directing reactants to the membrane electrode assembly.
In the system illustrated in
FIG. 1
, the fuel processing subsystem comprises compressor
102
, pre-oxidizer cooler
104
, pre-oxidizer
106
, hydrodesulfurizer
108
, hydrogenator
110
, evaporator
112
, regenerator heat exchanger
114
, furnace
116
(comprising a reformer), shift reactor precooler
118
, shift reactor first stage
120
, intercooler
122
, shift reactor second stage
124
, hydrogen recycle compressor
126
, selective oxidizer pre-cooler
128
, selective oxidizer
130
, fuel filter
132
, anode pre-cooler
134
, and water separator
136
.
The raw inlet fuel stream is directed to the fuel processing subsystem via compressor
102
. Most of the raw inlet fuel stream is directed to downstream fuel processing components. A small portion of the raw inlet fuel stream is directed to auxiliary burner
138
.
The raw inlet fuel stream is first directed through preoxidizer cooler
104
and preoxidizer
106
. In preoxidizer
106
, oxygen from peak shave gas is consumed. Peak shave gas is a mixture of air and propane that is occasionally added to natural gas during peak demand periods. Preoxidizer
106
is not required if the raw inlet fuel stream does not comprise any oxygen, for example, as in the case where peak shave gas is not employed and the raw inlet fuel stream is propane or natural gas.
Next, sulfur is removed from the inlet fuel stream. A desulfurizer such as hydrodesulfurizer
108
may be employed to accomplish this step. The inlet fuel stream that passes through hydrodesulfurizer
108
contacts a catalyst that causes the sulfur to react with hydrogen to form hydrogen sulfide. Hydrogen needed for this reaction is provided by hydrogen recycle compressor
126
, which directs a portion of the processed (reformate) hydrogen-rich fuel stream back into the raw inlet fuel stream upstream of hydrodesulfurizer
108
. Inside hydrodesulfurizer
108
, after contacting the catalyst, the fuel stream then passes over a bed of zinc oxide and the hydrogen sulfide reacts to form solid zinc sulfide and water.
Upon exiting hydrodesulfurizer
108
, the desulfurized fuel stream, which still contains some residual hydrogen, is directed to hydrogenator
110
in which it passes through a bed of hydrogenation catalyst that induces the hydrogen to react with unsaturated hydrocarbons (for example, olefins) to produce saturated hydrocarbons.
The fuel stream exiting hydrogenator
110
is then directed to evaporator
112
where the fuel stream is humidified by mixing it with a fine spray of water. For example, evaporator
112
may be a co-current flow vaporizer having a low pressure drop design. The humidified fuel stream exits evaporator
112
at about 350-360° F. (177-182° C.), so the water entrained therein is substantially vaporized. The heat for evaporator
112
is supplied by the burner exhaust stream, which originates from reformer furnace
116
.
The humidified fuel stream exiting evaporator
112
is then directed through regenerator heat exchanger
114
. In regenerator heat exchanger
114
heat is exchanged between the hot reformate fuel stream exiting furnace
116
and the humidified fuel stream which is being directed toward the reformer in furnace
116
. The temperature of the humidified fuel stream leaving regenerator heat exchanger
114
is approximately 650° F. (343° C.).
The humidified and heated fuel stream is then directed to the reformer that is located within furnace
116
. A catalyst is provided inside the reformer to induce the desired endothermic chemical reactions that convert the humidified fuel stream into a reformate fuel stream. Furnace burner
140
provides the heat that is required to maintain the desired endothermic reaction. The reformate fuel stream also comprises carbon dioxide, carbon monoxide, and water vapor. The reformate fuel stream leaves reformer furnace
116
with a temperature of approximately 850° F. (454° C.).
As mentioned above, after exiting reformer furnace
116
, the reformate fuel stream is directed to regenerator heat exchanger
114
(where the heat from the reformate fuel stream is used to preheat the humidified fuel stream upstream of the reformer). The reformate fuel stream leaving regenerator heat exchanger
114
has a temperature of approximately 580° F. (304° C.). The reformate fuel stream is further cooled in shift reactor precooler
118
where heat is transferred to an oxidant stream before it is fed to furnace burner
140
.
The reformate fuel stream exiting shift reactor precooler
Cownden Ryan
Eiche Michael
Louie Craig
Watkins David S.
Ballard Generation Systems Inc.
McAndrews Held & Malloy Ltd.
Ryan Patrick
Yuan Dah-Wei D
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