WO2000039875A1 - A hydrocarbon fueled power plant employing a proton exchange membrane (pem) fuel cell - Google Patents

A hydrocarbon fueled power plant employing a proton exchange membrane (pem) fuel cell Download PDF

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Publication number
WO2000039875A1
WO2000039875A1 PCT/US1999/030263 US9930263W WO0039875A1 WO 2000039875 A1 WO2000039875 A1 WO 2000039875A1 US 9930263 W US9930263 W US 9930263W WO 0039875 A1 WO0039875 A1 WO 0039875A1
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Prior art keywords
fuel
reactant gas
fuel cell
power plant
reformer
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PCT/US1999/030263
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French (fr)
Inventor
Leslie L. Van Dine
Paul J. Farris
Valerie A. Maston
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International Fuel Cells, Llc
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Application filed by International Fuel Cells, Llc filed Critical International Fuel Cells, Llc
Priority to AU21975/00A priority Critical patent/AU2197500A/en
Publication of WO2000039875A1 publication Critical patent/WO2000039875A1/en

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    • H—ELECTRICITY
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    • H01M8/00—Fuel cells; Manufacture thereof
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    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/48—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents followed by reaction of water vapour with carbon monoxide
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    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/56—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
    • C01B3/58—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction
    • C01B3/583—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction the reaction being the selective oxidation of carbon monoxide
    • H—ELECTRICITY
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    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
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    • C01B2203/0838—Methods of heating the process for making hydrogen or synthesis gas by heat exchange with exothermic reactions, other than by combustion of fuel
    • C01B2203/0844—Methods of heating the process for making hydrogen or synthesis gas by heat exchange with exothermic reactions, other than by combustion of fuel the non-combustive exothermic reaction being another reforming reaction as defined in groups C01B2203/02 - C01B2203/0294
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
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    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
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    • C01B2203/1264—Catalytic pre-treatment of the feed
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    • C01B2203/1288—Evaporation of one or more of the different feed components
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    • C01B2203/146—At least two purification steps in series
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    • C01B2203/16—Controlling the process
    • C01B2203/1614—Controlling the temperature
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0082—Organic polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04029—Heat exchange using liquids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency

Definitions

  • This invention relates to a power plant fueled by hydrocarbon fuel and employing a proton exchange membrane (PEM) fuel cell.
  • PEM proton exchange membrane
  • the fuel cell itself consists of an anode, a cathode and an electrolyte that separates the two.
  • Fuel reactant gas which is typically a hydrogen rich stream, enters the anode of the fuel cell and oxidant reactant gas, which is commonly air, enters the cathode of the fuel cell.
  • a catalyst in the anode causes the hydrogen to oxidize resulting in the creation of hydrogen ions, which pass through the electrolyte to the cathode, thereby creating an electric potential across the fuel cell.
  • the electrolyte is the ionic conducting substance between the anode and the cathode.
  • One type of fuel cell includes an acid electrolyte, such as phosphoric acid (H 3 P0 4 ), typically operating at a temperature range of about 190°C (375°F) to about 218°C (425 °F).
  • Another type of electrolyte includes a membrane electrolyte, such as a solid polymer electrolyte or otherwise referred to as a proton exchange membrane (PEM).
  • PEM proton exchange membrane
  • Fuel cells incorporating a proton exchange membrane will hereinafter be referred to as a PEM fuel cell, which typically operate at a temperature range of about 82°C (180°F) to about 93°C (200°F).
  • Utilizing a phosphoric acid electrolyte fuel cell that operates at a temperature range of about 190°C (375°F) to about 218°C (425°F) within a power plant offers two (2) advantages.
  • One advantage includes the option of fueling the phosphoric acid electrolyte power plant with a hydrocarbon fuel, such as natural gas, rather than fueling it directly with pure hydrogen.
  • the power plant In order to fuel the power plant with a hydrocarbon fuel, the power plant must include a fuel processor, such as a reformer, which converts the hydrocarbon fuel into a hydrogen rich stream. While converting hydrocarbon fuel to hydrogen, the fuel processor also produces carbon monoxide (CO) and carbon dioxide (CO 2 ).
  • a phosphoric acid electrolyte fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F) can withstand up to about one percent (1 %) of carbon monoxide in the fuel reactant gas before its presence begins to inhibit the anode performance.
  • a PEM fuel cell can only withstand less than about ten parts per million per volume (ppmv) of CO in the fuel reactant gas before the CO inhibits the chemical reaction from occurring in the anode at an acceptable rate.
  • the other advantage of utilizing a phosphoric acid electrolyte fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F) is that the waste heat from the electrochemical reaction at the anode and cathode allows the fuel cell cooling system to generate the steam required by the reformer.
  • reformers such as thermal steam reformers, adiabatic reformers and hybrid reformers.
  • a thermal steam reformer as described in U.S. Patent Nos. 4,098,587 and 4,098,588 which are hereby incorporated by reference, is typically used to convert natural gas, which is mostly methane, to a hydrogen rich fuel reactant gas.
  • the thermal steam reformer combines the hydrocarbon fuel and the steam, thereby initiating the chemical reaction of CH 4 + 2H 2 O ⁇ CO 2 + 4H and producing a hydrogen rich fuel reactant gas.
  • a PEM fuel cell fails to produce the steam required by the thermal steam reformer because the PEM fuel cell operates at about ambient pressure and at a temperature range of about 82°C (180°F) to about 93°C (200°F).
  • the operating temperature of a phosphoric acid electrolyte fuel cell power plant increases the overall cost of the power plant because the power plant must include certain equipment constructed of materials that are capable of withstanding the detrimental effects associated with a fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F).
  • One detrimental effect includes the difficulty of managing steam at this temperature range within the coolant system. It is desirable, therefore, to design a fuel cell power plant that operates at a lower temperature while maintaining equivalent fuel cell performance.
  • One such means includes replacing the phosphoric acid electrolyte fuel cell with a PEM fuel cell.
  • the PEM fuel cell has many advantages related to its high performance characteristics at low operating temperatures and pressure.
  • the PEM fuel cell has higher performance characteristics compared to the phosphoric acid fuel cell, thereby permitting the incorporation of smaller, less expensive fuel cells in order to produce an equivalent amount of power.
  • the operating temperature of a PEM fuel cell permits the use of a greater variety of materials, thereby accomplishing construction of the fuel cell and the power plant with potentially less expensive material.
  • the PEM fuel cell is susceptible to performance losses if the concentration of CO in the fuel reactant gas is greater than about ten ppmv. Therefore, current designs of power plants employing a PEM fuel cell are fueled by pure hydrogen rather than hydrocarbon fuel because fueling the PEM fuel cell with pure hydrogen provides assurance that the fuel reactant gas will not include CO. Furthermore, the low operating temperature of the PEM fuel cell fails to increase the temperature of the cooling loop such that steam is produced, as is in the cooling loop of the phosphoric acid fuel cell. Although the operating temperature of the PEM fuel cell reduces pressure in the cooling stream, thereby allowing for a simpler and less expensive cooling system, a source of steam required by the reformer to convert the hydrocarbon fuel into the fuel reactant gas is lost. What is needed is a power plant capable of operating at lower fuel cell temperatures and coolant pressures such that the overall size and manufacturing cost of the power plant is reduced while maintaining the advantages provided by an acid electrolyte fuel cell power plant that is fueled by hydrocarbon fuel.
  • the present invention relates to a hydrocarbon fueled power plant, which converts a hydrocarbon fuel to a hydrogen rich fuel reactant gas and delivers such fuel reactant gas, along with oxidant reactant gas, to a PEM fuel cell operating at about ambient pressure and producing electricity as a result of the electrochemical reaction between the anode and cathode.
  • the present invention receives hydrocarbon fuel that is converted to a to a hydrogen rich fuel reactant gas having a concentration of carbon monoxide less than about ten ppmv before it enters the anode of the PEM fuel cell.
  • the power plant of the present invention includes a reformer and a PEM fuel cell.
  • the present invention also includes a shift converter and a selective oxidizer located between the reformer and PEM fuel cell in order to reduce the concentration of carbon monoxide to an acceptable level.
  • the power plant of the present invention further includes a boiler.
  • the boiler provides steam to the reformer, which also receives the hydrocarbon fuel and converts the hydrocarbon fuel into a fuel reactant gas that consists mainly of hydrogen.
  • Incorporating the boiler into the PEM fuel cell power plant provides the reformer with a source of steam, which was lost when the PEM fuel cell replaced the acid electrolyte fuel cell.
  • Combining the boiler, reformer, shift converter, selective oxidizer, and a PEM fuel cell creates an ambient pressure power plant utilizing hydrocarbon fuel.
  • the operating pressure of the power plant, including the steam provided by the boiler is about 0.146 Kg/cm 2 (2 psig) to about 0.352 Kg/cm 2 (5 psig).
  • the hydrocarbon fueled PEM fuel cell power plant does not fall within the scope of some boiler code regulations, thereby reducing the cost of manufacturing and operating such a system.
  • the present invention therefore, maintains the advantages provided by an acid electrolyte fuel cell power plant while reducing the operating coolant stream pressure and fuel cell temperature of a power plant such that the overall size and manufacturing cost of the power plant is decreased.
  • Fig. 1 is a schematic diagram of a power plant, which includes a PEM fuel cell capable of operating at about ambient pressure and incorporating the features of the present invention.
  • Fig. 2 is a schematic diagram of an optional cooling loop for the PEM fuel cell.
  • FIG. 1 there is shown an PEM fuel cell (hereinafter referred to as a "fuel cell”) in a power plant 10 wherein the fuel cell is designated by the numeral 12.
  • a power plant 10 typically consists of a plurality of fuel cells, which are called a cell stack assembly and connected electrically in series, for the purposes of simplicity in explaining the present invention, the block representing the fuel cell 12 illustrates only one fuel cell.
  • Each fuel cell 12 includes a proton exchange membrane 20 disposed adjacent to and between an anode 14 and a cathode 16.
  • the electrochemical reaction results in an increase in temperature within the fuel cell 12, thereby necessitating a means for cooling the fuel cell 12.
  • One such means includes a cooler 18, which is disposed on the side of the cathode 16 opposite of the anode 14, and a cooling loop, which is indicated generally by numeral 22.
  • coolers There are various types of coolers known in the art, but the cooling system for a PEM fuel cell has different requirements in comparison to an acid electrolyte fuel cell because the PEM fuel cell operates with the coolant stream interconnected to the reactant gases through a porous graphite plate separating the reactant gas passages from the water coolant channels. These porous plates facilitate the addition or removal of water from the fuel cell.
  • Coolant fluid such as water is circulated through the cooling loop 22 via a pump 24, which can be a fixed or variable speed pump. As the coolant fluid passes through the cooler 18, it absorbs heat from the fuel cell 12. The temperature of the coolant fluid exits the fuel cell 12 at a range of about 60°C (140°F) to about 71 °C (160° F).
  • the coolant loop includes a heat exchanger 26 capable of reducing the temperature of the coolant fluid to about 130 °F.
  • the heat exchanger 26 can be a single pass heat exchanger or a dual pass heat exchanger.
  • the heat exchanger 26 will be controlled by a thermostat 28, which will sense the temperature of the cooling fluid exiting the heat exchanger 26.
  • the cooling loop 22 is essentially a closed loop system except for the addition of make-up water, which originates from a water treatment system 34.
  • the make-up water is introduced to the cooling loop 22 by line 32, which also serves as a bleed line for any excess product water produced in the fuel cell 12.
  • the controls and hardware required to maintain the cooling loop 22 at the appropriate pressure while bleeding out product water and bleeding in make-up water are commonly known in the art.
  • Oxidant reactant gas may be essentially pure oxygen or air.
  • the air source 36 will be ambient air delivered to the cathode 16 along line 38 by a blower or compressor 40. If the oxidant reactant gas is essentially pure oxygen, then the air source 36 will be a pressurized oxygen container (not illustrated). It may also be preferable to preheat the oxidant reactant gas prior entering the cathode 16. If so, a heat exchanger 44 may be inserted into line 38 between the air source 36 and the cathode 16. The gases entering the primary loop of the heat exchanger 44 along line 42 exit the heat exchanger 44 along line 46 and travel to a condenser 48 after which the gases are exhausted while the condensed water is fed to the water treatment system 34.
  • the cathode exhaust enters the secondary loop of the heat exchanger 44, thereby creating a heat exchange relationship between the oxidant reactant gas and the cathode exhaust, which increases the temperature of the oxidant reactant gas.
  • the anode 14 of the fuel cell 12 requires hydrogen gas as the fuel reactant gas.
  • the means for providing the fuel reactant gas to the anode 12 begins with a hydrocarbon fuel source 60, typically natural gas, which is mostly methane, but could include other hydrocarbon fuels such as methane, propane, or liquid fuel such as naphtha.
  • the hydrocarbon fuel enters a pump 64 along line 62 and exits along line 66.
  • the hydrocarbon fuel and the recycle stream enter the primary loop of a heat exchanger 68, which increases the temperature of the hydrocarbon fuel and recycle stream by creating a heat exchange relationship with the fuel reactant gas exiting the reformer 76 (discussed hereinafter) and entering the secondary loop of the heat exchanger along line 78.
  • Some of the heat exchangers illustrated in Fig. 1 are shown in duplicate locations in order to reduce the complexity of the schematic.
  • the heated hydrocarbon fuel and recycle stream collectively called the heated hydrocarbon fuel
  • the heated hydrocarbon fuel exit the heat exchanger 68 along line 70
  • the heated hydrocarbon fuel enters a hydro- desulfurizer 72.
  • the hydro-desulfurizer 72 may not be necessary, some hydrocarbon fuels include various amounts of sulfur, which may be damaging to the reformer 76 and shift converter 84.
  • hydro-desulfurizers which are commercially available and capable of removing the undesired sulfur.
  • the heated and desulfuhzed hydrocarbon fuel exits the hydro-desulfurizer 72 along line 74 and mixes with steam (e.g., heated water vapor) furnished to the power plant 10 by a boiler 56 along line 58.
  • the boiler 56 receives water along line 54 and converts the water to steam.
  • the steam is generated at a pressure ranging from about 0.146 Kg/cm 2 (2 psig) to 0.633 Kg/cm 2 (9 psig), which is a pressure sufficient to convey the steam through the fuel processing system.
  • the steam is generated at its saturation temperature and further heated to a higher temperature (i.e., superheated) to prepare it for use in reforming the hydrocarbon fuel and for preventing condensation in the process plumbing.
  • Incorporating the boiler into the power plant provides the reformer 76 with a source of steam, which was lost when the PEM fuel cell replaced the acid electrolyte fuel cell, because the PEM fuel cell operates at about ambient pressure and about 82°C (180°F) to about 93°C (200°F) while an acid electrolyte fuel cell operates at about 190°C (375°F) to about 218°C (400°F).
  • the water originates from a water treatment system 34 along line 50 and passes through the primary loop of a heat exchanger 52, which increases the temperature of the water before it reaches the boiler 56.
  • Fuel reactant gas exiting the reformer 76 enters the secondary loop of the heat exchanger 52 in line 80; thereby creating a heat exchange relationship between the two fluids and increasing the temperature of the water with the energy in the fuel reactant gas.
  • the steam and desulfuhzed fuel enter a reformer 76 along line 74.
  • the preferred ratio is about three moles of steam per atom of hydrocarbon fuel (e.g., 1 mole of methane (CH )).
  • thermal steam reformer is preferred when converting natural gas fuel to hydrogen.
  • a burner 100 fired by a mixture of the hydrocarbon fuel it receives along line 108 and the depleted fuel reactant gas along line 110 and humidified oxidant reactant gas along line 102, furnishes the reformer 76 with heat in order to convert the steam and desulfuhzed fuel into the fuel reactant gas.
  • a preferred type of reformer is the type shown in U.S. Patent Nos. 4,098,587 and 4,098,588.
  • the composition of the fuel reactant gas exiting the reformer 76 typically consists of hydrogen, water vapor, carbon monoxide and carbon dioxide.
  • the fuel reactant gas exiting the reformer 76 along line 78 enters the heat exchanger 68 (discussed hereinbefore), which creates a heat exchange relationship with the hydrocarbon fuel in line 66, thereby cooling the fuel reactant gas.
  • the fuel reactant gas exits the heat exchanger 68 along line 80 and enters the heat exchanger 52, which further cools the fuel reactant gas.
  • the heat exchanger 52 (discussed hereinbefore) creates a heat exchange relationship between the fuel reactant gas exiting the reformer 76 and the water exiting the water treatment system 34.
  • the heat exchangers within the power plant 10 are not required but are preferred because they increase the overall operating efficiency of the power plant.
  • the fuel reactant gas exits the heat exchanger 52 along line 82 and enters a shift converter 84, which converts a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide.
  • the shift converter 84 operates by the chemical reaction of CO + H 2 O ⁇ CO 2 + H 2 , thereby reducing the amount of carbon monoxide in the fuel reactant gas to about one percent (1 %).
  • shift converters There are a variety of shift converters commercially available to perform this task.
  • the composition of the fuel reactant gas includes an increased portion of hydrogen and carbon dioxide and a reduced portion of carbon monoxide.
  • a portion of the fuel reactant gas exiting the shift converter 84 is recycled along line 88 and mixed with the fuel in line 66, which both enter the heat exchanger 68.
  • the remainder of the fuel reactant gas enters a selective oxidizer 90 along line 86 which also receives oxidant reactant gas along line 104.
  • the selective oxidizer 90 further reduces the amount of carbon monoxide in the fuel reactant gas to a predetermined low level of about ten parts ppmv according to the following reaction: CO + 1 /2 ⁇ 2 ⁇ CO 2 .
  • a selective oxidizer 90 that includes two oxidation stages 92, 94 such as illustrated in U.S. Patent No. 5,330,727, which is hereby incorporated by reference.
  • a single stage selective oxidizer is capable of reducing the concentration of carbon monoxide in the fuel reactant gas to less than about ten ppmv, then only one oxidation stage is required. If, however, the selective oxidizer 90 does not reduce the level of carbon monoxide in the fuel reactant gas to the predetermined low level of about 10 ppmv of CO, then an additional oxidizer stage may be added to the power plant 10. This additional stage may be a separate selective oxidizer or an additional oxidizer bed as explained in U.S. Patent No. 5,330,727.
  • the fuel reactant gas exits the second selective oxidizer 90 along line 96 and enters the anode 14, thereby allowing the electrochemical reaction between the fuel reactant gas and the oxidant reactant gas to take place in the fuel cell 12 and produce electric power.
  • the depleted fuel reactant gas exits the anode 14 along line 110 and enters the burner 100, which consumes any remaining hydrogen in the fuel reactant gas to heat the reformer 76.
  • the cooling system 200 includes a fuel cell 12, a dual pass heat exchanger 26, a cooling tower 206, a pump 204, a condenser 202, a selective oxidizer 90 and a shift converter 84.
  • Cooling water which may include glycol (i.e., antifreeze), exits the cooling tower 206 along line 208 and enters a pump 204, which circulates the cooling water through the cooling system 200.
  • the cooling water thereafter, travels along line 210 and enters the condenser 202, which saturates the remainder of the cooling water.
  • the saturated cooling water exits the condenser 202 and enters the dual pass heat exchanger 26 along line 212.
  • the fuel cell cooling loop 22 can include either a single pass heat exchanger or a dual pass heat exchanger, and this options illustrates a dual pass heat exchanger.
  • the thermostat 28 senses the temperature of the cooling stream 22 upon exiting the heat exchanger 26 and controls the flow of cooling water entering the secondary loop of the heat exchanger along line 212 in order to maintain the temperature of the cooling stream 22 in the primary loop of the heat exchange 26 at a constant temperature.
  • the reactions occurring within the selective oxidizer 90 and the shift converter 84 are endothermic reactions, which require cooling. Therefore, the cooling system 200 passes through both devices.
  • the temperature of the selective oxidizer 90 and the shift converter 84 must be carefully controlled to ensure their efficient operation. It is preferable to cool the selective oxidizer 90 before cooling the shift converter 84 because the temperature of the cooling water increases as it passes through both devices, but the temperature of the cooling water entering the selective oxidizer 90, which reduces the concentration of carbon monoxide from about one percent (1%) to about ten ppmv, should be less than the temperature of the cooling water entering the shift converter 84, which reduces the concentration of carbon monoxide to about one percent (1%).
  • the cooling water should enter the last oxidation stage in the selective oxidizer 90 before entering any other oxidation stage in order to increase the efficiency of the selective oxidizer to reduce the concentration of carbon monoxide in the fuel reactant gas as much as possible prior to the fuel reactant gas entering the anode 14. Therefore, the cooling water exits the heat exchanger 26 along line 214 and enters the selective oxidizer 90. Within the selective oxidizer 90, the cooling water first passes through the second oxidation stage 94 and then passes through the first oxidation stage before exiting the selective oxidizer 90 along line 216. The cooling water, thereafter, cools the shift converter 84 and returns the cooling tower 206 along line 218.

Abstract

The present invention is a power plant (10) employing a proton exchange membrane (PEM) fuel cell (12). The PEM fuel cell power plant is fueled by a hydrocarbon fuel (60), which is converted to hydrogen rich fuel reactant gas stream by a reformer (76). A shift converter (84) and selective oxidizer (90) remove the majority of undesired carbon monoxide gases created by the reformer when converting the hydrocarbon fuel to hydrogen. The PEM fuel cell power plant also includes a boiler (56), which provides steam to the reformer, thereby allowing replacement of an acid electrolyte fuel cell in a power plant with a PEM fuel cell without compromising the advantages of the acid electrolyte fuel cell.

Description

DESCRIPTION
A Hydrocarbon Fueled Power Plant Employing a Proton Exchange
Membrane (PEM) Fuel Cell
Technical Field This invention relates to a power plant fueled by hydrocarbon fuel and employing a proton exchange membrane (PEM) fuel cell.
Background Art
Many industrial facilities utilize fuel cell power plants to satisfy both their daily and temporary need for electricity. The fuel cell itself consists of an anode, a cathode and an electrolyte that separates the two. Fuel reactant gas, which is typically a hydrogen rich stream, enters the anode of the fuel cell and oxidant reactant gas, which is commonly air, enters the cathode of the fuel cell. A catalyst in the anode causes the hydrogen to oxidize resulting in the creation of hydrogen ions, which pass through the electrolyte to the cathode, thereby creating an electric potential across the fuel cell.
There are several types of fuel cells, which vary according to their electrolyte. The electrolyte is the ionic conducting substance between the anode and the cathode. One type of fuel cell includes an acid electrolyte, such as phosphoric acid (H3P04), typically operating at a temperature range of about 190°C (375°F) to about 218°C (425 °F). Another type of electrolyte includes a membrane electrolyte, such as a solid polymer electrolyte or otherwise referred to as a proton exchange membrane (PEM). Fuel cells incorporating a proton exchange membrane will hereinafter be referred to as a PEM fuel cell, which typically operate at a temperature range of about 82°C (180°F) to about 93°C (200°F).
Utilizing a phosphoric acid electrolyte fuel cell that operates at a temperature range of about 190°C (375°F) to about 218°C (425°F) within a power plant offers two (2) advantages. One advantage includes the option of fueling the phosphoric acid electrolyte power plant with a hydrocarbon fuel, such as natural gas, rather than fueling it directly with pure hydrogen. In order to fuel the power plant with a hydrocarbon fuel, the power plant must include a fuel processor, such as a reformer, which converts the hydrocarbon fuel into a hydrogen rich stream. While converting hydrocarbon fuel to hydrogen, the fuel processor also produces carbon monoxide (CO) and carbon dioxide (CO2). Although the presence of CO2 in the fuel reactant gas may only affect the efficiency of the operation of the fuel cell, its presence will not inhibit the chemical reaction occurring in the anode. The presence of CO in the fuel reactant gas, however, will inhibit the chemical reaction and poison the anode if the fuel cell operates below a certain temperature and the percentage of CO is above a certain level. A phosphoric acid electrolyte fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F) can withstand up to about one percent (1 %) of carbon monoxide in the fuel reactant gas before its presence begins to inhibit the anode performance. As the operating temperature of the fuel cell decreases, while maintaining the same percentage of carbon monoxide in the fuel reactant gas, the carbon monoxide prevents the chemical reaction from occurring in the anode, thereby decreasing the performance of the fuel cell. For example, a PEM fuel cell can only withstand less than about ten parts per million per volume (ppmv) of CO in the fuel reactant gas before the CO inhibits the chemical reaction from occurring in the anode at an acceptable rate.
The other advantage of utilizing a phosphoric acid electrolyte fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F) is that the waste heat from the electrochemical reaction at the anode and cathode allows the fuel cell cooling system to generate the steam required by the reformer. It is known in the art that there are different types of reformers, such as thermal steam reformers, adiabatic reformers and hybrid reformers. A thermal steam reformer, as described in U.S. Patent Nos. 4,098,587 and 4,098,588 which are hereby incorporated by reference, is typically used to convert natural gas, which is mostly methane, to a hydrogen rich fuel reactant gas. The thermal steam reformer combines the hydrocarbon fuel and the steam, thereby initiating the chemical reaction of CH4 + 2H2O → CO2 + 4H and producing a hydrogen rich fuel reactant gas. A PEM fuel cell, however, fails to produce the steam required by the thermal steam reformer because the PEM fuel cell operates at about ambient pressure and at a temperature range of about 82°C (180°F) to about 93°C (200°F).
The operating temperature of a phosphoric acid electrolyte fuel cell power plant, however, increases the overall cost of the power plant because the power plant must include certain equipment constructed of materials that are capable of withstanding the detrimental effects associated with a fuel cell operating at a temperature range of about 190°C (375°F) to about 218°C (425°F). One detrimental effect includes the difficulty of managing steam at this temperature range within the coolant system. It is desirable, therefore, to design a fuel cell power plant that operates at a lower temperature while maintaining equivalent fuel cell performance. One such means includes replacing the phosphoric acid electrolyte fuel cell with a PEM fuel cell. The PEM fuel cell has many advantages related to its high performance characteristics at low operating temperatures and pressure. Namely, the PEM fuel cell has higher performance characteristics compared to the phosphoric acid fuel cell, thereby permitting the incorporation of smaller, less expensive fuel cells in order to produce an equivalent amount of power. In addition, the operating temperature of a PEM fuel cell permits the use of a greater variety of materials, thereby accomplishing construction of the fuel cell and the power plant with potentially less expensive material.
As mentioned above, the PEM fuel cell is susceptible to performance losses if the concentration of CO in the fuel reactant gas is greater than about ten ppmv. Therefore, current designs of power plants employing a PEM fuel cell are fueled by pure hydrogen rather than hydrocarbon fuel because fueling the PEM fuel cell with pure hydrogen provides assurance that the fuel reactant gas will not include CO. Furthermore, the low operating temperature of the PEM fuel cell fails to increase the temperature of the cooling loop such that steam is produced, as is in the cooling loop of the phosphoric acid fuel cell. Although the operating temperature of the PEM fuel cell reduces pressure in the cooling stream, thereby allowing for a simpler and less expensive cooling system, a source of steam required by the reformer to convert the hydrocarbon fuel into the fuel reactant gas is lost. What is needed is a power plant capable of operating at lower fuel cell temperatures and coolant pressures such that the overall size and manufacturing cost of the power plant is reduced while maintaining the advantages provided by an acid electrolyte fuel cell power plant that is fueled by hydrocarbon fuel.
Disclosure of Invention
Accordingly, the present invention relates to a hydrocarbon fueled power plant, which converts a hydrocarbon fuel to a hydrogen rich fuel reactant gas and delivers such fuel reactant gas, along with oxidant reactant gas, to a PEM fuel cell operating at about ambient pressure and producing electricity as a result of the electrochemical reaction between the anode and cathode. The present invention receives hydrocarbon fuel that is converted to a to a hydrogen rich fuel reactant gas having a concentration of carbon monoxide less than about ten ppmv before it enters the anode of the PEM fuel cell. Specifically, the power plant of the present invention includes a reformer and a PEM fuel cell. The present invention also includes a shift converter and a selective oxidizer located between the reformer and PEM fuel cell in order to reduce the concentration of carbon monoxide to an acceptable level.
The power plant of the present invention further includes a boiler. The boiler provides steam to the reformer, which also receives the hydrocarbon fuel and converts the hydrocarbon fuel into a fuel reactant gas that consists mainly of hydrogen. Incorporating the boiler into the PEM fuel cell power plant provides the reformer with a source of steam, which was lost when the PEM fuel cell replaced the acid electrolyte fuel cell. Combining the boiler, reformer, shift converter, selective oxidizer, and a PEM fuel cell creates an ambient pressure power plant utilizing hydrocarbon fuel. In addition, the operating pressure of the power plant, including the steam provided by the boiler, is about 0.146 Kg/cm2 (2 psig) to about 0.352 Kg/cm2 (5 psig). Because the operating pressure is below 1.055 Kg/cm2 (15 psig), the hydrocarbon fueled PEM fuel cell power plant does not fall within the scope of some boiler code regulations, thereby reducing the cost of manufacturing and operating such a system. The present invention, therefore, maintains the advantages provided by an acid electrolyte fuel cell power plant while reducing the operating coolant stream pressure and fuel cell temperature of a power plant such that the overall size and manufacturing cost of the power plant is decreased. The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.
Brief Description of Drawings
Fig. 1 is a schematic diagram of a power plant, which includes a PEM fuel cell capable of operating at about ambient pressure and incorporating the features of the present invention.
Fig. 2 is a schematic diagram of an optional cooling loop for the PEM fuel cell.
Best Mode for Carrying out the Invention
Referring to Fig. 1 , there is shown an PEM fuel cell (hereinafter referred to as a "fuel cell") in a power plant 10 wherein the fuel cell is designated by the numeral 12. Although a power plant 10 typically consists of a plurality of fuel cells, which are called a cell stack assembly and connected electrically in series, for the purposes of simplicity in explaining the present invention, the block representing the fuel cell 12 illustrates only one fuel cell. Each fuel cell 12 includes a proton exchange membrane 20 disposed adjacent to and between an anode 14 and a cathode 16. As a fuel reactant gas passes through the anode 14 hydrogen ions are produced and pass through the proton exchange membrane 20 to the cathode 16, which also receives oxidant gas, thereby creating an electrical connection across the fuel cell 12 and completing the circuit when an external load is applied.
The electrochemical reaction, however, results in an increase in temperature within the fuel cell 12, thereby necessitating a means for cooling the fuel cell 12. One such means includes a cooler 18, which is disposed on the side of the cathode 16 opposite of the anode 14, and a cooling loop, which is indicated generally by numeral 22. There are various types of coolers known in the art, but the cooling system for a PEM fuel cell has different requirements in comparison to an acid electrolyte fuel cell because the PEM fuel cell operates with the coolant stream interconnected to the reactant gases through a porous graphite plate separating the reactant gas passages from the water coolant channels. These porous plates facilitate the addition or removal of water from the fuel cell. This results in the coolant system being an integrated part of the fuel cell water management system, thereby further complicating the parameters of the cooling means. Removing product water from the fuel cell in conjunction with passing cooling fluid through the fuel cell 12 which operates at about ambient pressure requires careful control of the pressure in the cooling loop, oxidant reactant gas and fuel reactant gas. An exemplary type of management system for cooling a PEM is described in commonly owned U.S. Patent Nos. 5,503,944 and 5,700,595 which are both hereby incorporated by reference.
Coolant fluid such as water is circulated through the cooling loop 22 via a pump 24, which can be a fixed or variable speed pump. As the coolant fluid passes through the cooler 18, it absorbs heat from the fuel cell 12. The temperature of the coolant fluid exits the fuel cell 12 at a range of about 60°C (140°F) to about 71 °C (160° F). The coolant loop includes a heat exchanger 26 capable of reducing the temperature of the coolant fluid to about 130 °F. The heat exchanger 26 can be a single pass heat exchanger or a dual pass heat exchanger. The heat exchanger 26 will be controlled by a thermostat 28, which will sense the temperature of the cooling fluid exiting the heat exchanger 26. If the heat exchanger 26 is a single pass heat exchanger (as illustrated), then the thermostat 28 will control a fan 30, which will pass air over the heat exchanger 26. If the heat exchanger 26 is a dual pass heat exchanger, then the thermostat 28 will control the flow of an auxiliary cooling loop (not shown). The cooling loop 22 is essentially a closed loop system except for the addition of make-up water, which originates from a water treatment system 34. The make-up water is introduced to the cooling loop 22 by line 32, which also serves as a bleed line for any excess product water produced in the fuel cell 12. The controls and hardware required to maintain the cooling loop 22 at the appropriate pressure while bleeding out product water and bleeding in make-up water are commonly known in the art. Oxidant reactant gas may be essentially pure oxygen or air. As illustrated, if the oxidant reactant gas is air, then the air source 36 will be ambient air delivered to the cathode 16 along line 38 by a blower or compressor 40. If the oxidant reactant gas is essentially pure oxygen, then the air source 36 will be a pressurized oxygen container (not illustrated). It may also be preferable to preheat the oxidant reactant gas prior entering the cathode 16. If so, a heat exchanger 44 may be inserted into line 38 between the air source 36 and the cathode 16. The gases entering the primary loop of the heat exchanger 44 along line 42 exit the heat exchanger 44 along line 46 and travel to a condenser 48 after which the gases are exhausted while the condensed water is fed to the water treatment system 34. As the oxidant reactant gas passes through the primary loop, the cathode exhaust enters the secondary loop of the heat exchanger 44, thereby creating a heat exchange relationship between the oxidant reactant gas and the cathode exhaust, which increases the temperature of the oxidant reactant gas.
The anode 14 of the fuel cell 12 requires hydrogen gas as the fuel reactant gas. The means for providing the fuel reactant gas to the anode 12 begins with a hydrocarbon fuel source 60, typically natural gas, which is mostly methane, but could include other hydrocarbon fuels such as methane, propane, or liquid fuel such as naphtha. The hydrocarbon fuel enters a pump 64 along line 62 and exits along line 66. A recycle fuel stream 88 originating from the output of the shift converter 84 and indicated by a bullet marked "A" (discussed hereinafter), mixes with the hydrocarbon fuel in line 66. The hydrocarbon fuel and the recycle stream enter the primary loop of a heat exchanger 68, which increases the temperature of the hydrocarbon fuel and recycle stream by creating a heat exchange relationship with the fuel reactant gas exiting the reformer 76 (discussed hereinafter) and entering the secondary loop of the heat exchanger along line 78. Some of the heat exchangers illustrated in Fig. 1 are shown in duplicate locations in order to reduce the complexity of the schematic. As the heated hydrocarbon fuel and recycle stream, collectively called the heated hydrocarbon fuel, exit the heat exchanger 68 along line 70, the heated hydrocarbon fuel enters a hydro- desulfurizer 72. Although the hydro-desulfurizer 72 may not be necessary, some hydrocarbon fuels include various amounts of sulfur, which may be damaging to the reformer 76 and shift converter 84. There are a variety of hydro-desulfurizers, which are commercially available and capable of removing the undesired sulfur. The heated and desulfuhzed hydrocarbon fuel exits the hydro-desulfurizer 72 along line 74 and mixes with steam (e.g., heated water vapor) furnished to the power plant 10 by a boiler 56 along line 58. The boiler 56 receives water along line 54 and converts the water to steam. The steam is generated at a pressure ranging from about 0.146 Kg/cm2 (2 psig) to 0.633 Kg/cm2 (9 psig), which is a pressure sufficient to convey the steam through the fuel processing system. The steam is generated at its saturation temperature and further heated to a higher temperature (i.e., superheated) to prepare it for use in reforming the hydrocarbon fuel and for preventing condensation in the process plumbing. Incorporating the boiler into the power plant provides the reformer 76 with a source of steam, which was lost when the PEM fuel cell replaced the acid electrolyte fuel cell, because the PEM fuel cell operates at about ambient pressure and about 82°C (180°F) to about 93°C (200°F) while an acid electrolyte fuel cell operates at about 190°C (375°F) to about 218°C (400°F). The water originates from a water treatment system 34 along line 50 and passes through the primary loop of a heat exchanger 52, which increases the temperature of the water before it reaches the boiler 56. Fuel reactant gas exiting the reformer 76 enters the secondary loop of the heat exchanger 52 in line 80; thereby creating a heat exchange relationship between the two fluids and increasing the temperature of the water with the energy in the fuel reactant gas. The steam and desulfuhzed fuel enter a reformer 76 along line 74. The preferred ratio is about three moles of steam per atom of hydrocarbon fuel (e.g., 1 mole of methane (CH )). Although there are various types of reformers such as thermal steam reformers, adiabatic reformers, hybrid reformers and cyclic reformers which could all be used in the present invention, a thermal steam reformer is preferred when converting natural gas fuel to hydrogen. A burner 100, fired by a mixture of the hydrocarbon fuel it receives along line 108 and the depleted fuel reactant gas along line 110 and humidified oxidant reactant gas along line 102, furnishes the reformer 76 with heat in order to convert the steam and desulfuhzed fuel into the fuel reactant gas. A preferred type of reformer is the type shown in U.S. Patent Nos. 4,098,587 and 4,098,588. The composition of the fuel reactant gas exiting the reformer 76 typically consists of hydrogen, water vapor, carbon monoxide and carbon dioxide. The fuel reactant gas exiting the reformer 76 along line 78 enters the heat exchanger 68 (discussed hereinbefore), which creates a heat exchange relationship with the hydrocarbon fuel in line 66, thereby cooling the fuel reactant gas. The fuel reactant gas exits the heat exchanger 68 along line 80 and enters the heat exchanger 52, which further cools the fuel reactant gas. The heat exchanger 52 (discussed hereinbefore) creates a heat exchange relationship between the fuel reactant gas exiting the reformer 76 and the water exiting the water treatment system 34. The heat exchangers within the power plant 10 are not required but are preferred because they increase the overall operating efficiency of the power plant. The fuel reactant gas exits the heat exchanger 52 along line 82 and enters a shift converter 84, which converts a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide. The shift converter 84 operates by the chemical reaction of CO + H2O → CO2 + H2, thereby reducing the amount of carbon monoxide in the fuel reactant gas to about one percent (1 %). There are a variety of shift converters commercially available to perform this task. As the fuel reactant gas exits the shift converter along line 86, the composition of the fuel reactant gas includes an increased portion of hydrogen and carbon dioxide and a reduced portion of carbon monoxide. A portion of the fuel reactant gas exiting the shift converter 84 is recycled along line 88 and mixed with the fuel in line 66, which both enter the heat exchanger 68.
The remainder of the fuel reactant gas enters a selective oxidizer 90 along line 86 which also receives oxidant reactant gas along line 104. The selective oxidizer 90 further reduces the amount of carbon monoxide in the fuel reactant gas to a predetermined low level of about ten parts ppmv according to the following reaction: CO + 1/2θ2 → CO2. Although it is not necessary, it is preferable to use a selective oxidizer 90 that includes two oxidation stages 92, 94 such as illustrated in U.S. Patent No. 5,330,727, which is hereby incorporated by reference. If a single stage selective oxidizer is capable of reducing the concentration of carbon monoxide in the fuel reactant gas to less than about ten ppmv, then only one oxidation stage is required. If, however, the selective oxidizer 90 does not reduce the level of carbon monoxide in the fuel reactant gas to the predetermined low level of about 10 ppmv of CO, then an additional oxidizer stage may be added to the power plant 10. This additional stage may be a separate selective oxidizer or an additional oxidizer bed as explained in U.S. Patent No. 5,330,727. The fuel reactant gas exits the second selective oxidizer 90 along line 96 and enters the anode 14, thereby allowing the electrochemical reaction between the fuel reactant gas and the oxidant reactant gas to take place in the fuel cell 12 and produce electric power. The depleted fuel reactant gas exits the anode 14 along line 110 and enters the burner 100, which consumes any remaining hydrogen in the fuel reactant gas to heat the reformer 76. Referring to Fig. 2, there is shown a cooling system 200 for the power plant 10. The cooling system 200 includes a fuel cell 12, a dual pass heat exchanger 26, a cooling tower 206, a pump 204, a condenser 202, a selective oxidizer 90 and a shift converter 84. Cooling water, which may include glycol (i.e., antifreeze), exits the cooling tower 206 along line 208 and enters a pump 204, which circulates the cooling water through the cooling system 200. The cooling water, thereafter, travels along line 210 and enters the condenser 202, which saturates the remainder of the cooling water. The saturated cooling water exits the condenser 202 and enters the dual pass heat exchanger 26 along line 212. As mentioned above, the fuel cell cooling loop 22 can include either a single pass heat exchanger or a dual pass heat exchanger, and this options illustrates a dual pass heat exchanger. Therefore, the thermostat 28 senses the temperature of the cooling stream 22 upon exiting the heat exchanger 26 and controls the flow of cooling water entering the secondary loop of the heat exchanger along line 212 in order to maintain the temperature of the cooling stream 22 in the primary loop of the heat exchange 26 at a constant temperature.
The reactions occurring within the selective oxidizer 90 and the shift converter 84 are endothermic reactions, which require cooling. Therefore, the cooling system 200 passes through both devices. The temperature of the selective oxidizer 90 and the shift converter 84 must be carefully controlled to ensure their efficient operation. It is preferable to cool the selective oxidizer 90 before cooling the shift converter 84 because the temperature of the cooling water increases as it passes through both devices, but the temperature of the cooling water entering the selective oxidizer 90, which reduces the concentration of carbon monoxide from about one percent (1%) to about ten ppmv, should be less than the temperature of the cooling water entering the shift converter 84, which reduces the concentration of carbon monoxide to about one percent (1%). Furthermore, the cooling water should enter the last oxidation stage in the selective oxidizer 90 before entering any other oxidation stage in order to increase the efficiency of the selective oxidizer to reduce the concentration of carbon monoxide in the fuel reactant gas as much as possible prior to the fuel reactant gas entering the anode 14. Therefore, the cooling water exits the heat exchanger 26 along line 214 and enters the selective oxidizer 90. Within the selective oxidizer 90, the cooling water first passes through the second oxidation stage 94 and then passes through the first oxidation stage before exiting the selective oxidizer 90 along line 216. The cooling water, thereafter, cools the shift converter 84 and returns the cooling tower 206 along line 218.
Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made without departing from the spirit and scope of the invention.

Claims

Claims
1. An PEM fuel cell power plant, comprising:
(a) a cell stack assembly of PEM fuel cells, each fuel cell comprising a cathode, an anode and a proton exchange membrane disposed between said cathode and anode; (b) means for cooling said cell stack assembly;
(c) means for providing an oxidant reactant gas to said cathode;
(d) means for providing a fuel reactant gas to said anode, said fuel reactant gas means comprising:
(1 ) a boiler for producing steam; (2) a reformer for receiving the hydrocarbon fuel and the steam, said reformer producing a fuel reactant gas comprising hydrogen and carbon monoxide;
(3) a shift converter for receiving the fuel reactant gas from said reformer and converting a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide; and
(4) a selective oxidizer for receiving the fuel reactant gas from said shift converter and oxidant reactant gas from said oxidant reactant means, said first selective oxidizer converting a further portion of the carbon monoxide in the fuel reactant gas to carbon dioxide.
2. The PEM fuel cell power plant of claim 1 further comprising a second selective oxidizer for receiving the fuel reactant gas from said selective oxidizer and oxidant gas from said oxidant reactant means, said second selective oxidizer converting a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide.
3. The PEM fuel cell power plant of claim 1 wherein said selective oxidizer comprises one oxidizer stage.
4. The PEM fuel cell power plant of claim 1 wherein said selective oxidizer comprises at least two oxidizer stages.
5. The PEM fuel cell power plant of claim 1 wherein said means for providing a fuel reactant gas to said anode further comprises a burner for receiving the fuel reactant gas exiting said anode, said burner heating said reformer.
6. The PEM fuel cell power plant of claim 1 wherein said means for providing a fuel reactant gas to said anode further comprises:
(1) a hydro-desulfurizer located prior to said reformer;
(2) a heat exchanger located between said fuel source and said hydro-desulfurizer, said heat exchanger receiving the hydrocarbon fuel, said heat exchanger creating a heat exchange relationship between the hydrocarbon fuel and the fuel reactant gas exiting said reformer.
7. The PEM fuel cell power plant of claim 6 wherein said heat exchanger also receives a portion of the fuel reactant gas exiting said shift converter.
8. The PEM fuel cell power plant of claim 7 further comprising: (1 ) a water treatment system for supplying water to said boiler;
(2) a second heat exchanger located between said heat exchanger and said shift converter, said second heat exchanger creating a heat exchange relationship between the water exiting said water treatment system and the fuel reactant gas exiting said heat exchanger.
9. The PEM fuel cell power plant of claim 8 further comprising means for condensing water vapor emitted from said reformer and the condensed water vapor entering said water treatment system
10. The PEM fuel cell power plant of claim 9 further comprising a third heat exchanger in a heat exchange relationship between the water vapor emitted from said cathode of said fuel cell and the oxidant reactant gas.
11. A method for operating a PEM fuel cell power plant, said power plant having a cell stack assembly of polymer electrolyte fuel cells, each fuel cell having a cathode, an anode and a proton exchange membrane disposed between said cathode and anodes, said method comprising the steps of:
(a) providing an oxidant reactant gas to said cathode;
(b) supplying water to a boiler for producing heated water vapor;
(c) supplying a hydrocarbon fuel and the heated water vapor to a reformer for producing a fuel reactant gas comprising hydrogen and carbon monoxide;
(d) supplying the fuel reactant gas exiting the reformer to a shift converter for converting a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide and hydrogen;
(e) supplying the fuel reactant gas exiting the shift converter to a selective oxidizer for converting a portion of the carbon monoxide in the fuel reactant gas to carbon dioxide; (f) conveying the fuel reactant gas from the selective oxidizer to said anode; and (g) supplying cooling fluid to the cell stack assembly.
12. The method of claim 11 wherein said anode exhausts any unused fuel reactant gas to a burner which heats the reformer.
13. The method of claim 1 1 further comprising the steps of:
(a) heating the hydrocarbon fuel by creating a heat exchange relationship with the fuel reactant gas exiting the reformer; (b) removing at least a portion of sulfur in the hydrocarbon fuel before the hydrocarbon fuel enters the reformer;
14. The method of claim 13 further comprising the step of adding a portion of the fuel reactant gas to the hydrocarbon fuel before heating the hydrocarbon fuel.
15. The method of claim 14 further comprising the step of further comprising the step of cooling the fuel reactant gas exiting the reformer by creating a heat exchange relationship with water exiting a water treatment system.
16. The method of claim 15 further comprising the step of further comprising the step of condensing water vapor emitted from the reformer.
17. The method of claim 16 further comprising the step of further comprising the step of cooling the water vapor emitted from the cathode of the fuel cell by creating a heat exchange relationship with the oxidant reactant gas.
PCT/US1999/030263 1998-12-23 1999-12-17 A hydrocarbon fueled power plant employing a proton exchange membrane (pem) fuel cell WO2000039875A1 (en)

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WO2004106226A1 (en) * 2003-05-23 2004-12-09 Exxonmobil Research And Engineering Company Method for producing electricity using temperature swing reforming and solid oxide fuel cell
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FR2876500A1 (en) * 2004-10-08 2006-04-14 Renault Sas ELECTRICITY GENERATOR FOR MOTOR VEHICLE
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