Patent Application
20080248369
1. Field of the Invention
The present invention relates generally to fuel cell systems, and, more particularly, to a fuel cell system comprising a flame arresting recombiner.
2. Description of the Related Art
Electrochemical fuel cells convert reactants, namely fuel and oxidant fluid streams, to generate electric power and reaction products. Electrochemical fuel cells generally employ an electrolyte disposed between two electrodes, namely a cathode and an anode. An electrocatalyst, disposed at the interfaces between the electrolyte and the electrodes, typically induces the desired electrochemical reactions at the electrodes. The location of the electrocatalyst generally defines the electrochemically active area.
One type of electrochemical fuel cell is the polymer electrolyte membrane (PEM) fuel cell. PEM fuel cells generally employ a membrane electrode assembly (MEA) comprising a solid polymer electrolyte or ion-exchange membrane disposed between two electrodes. Each electrode typically comprises a porous, electrically conductive substrate, such as carbon fiber paper or carbon cloth, which provides structural support to the membrane and serves as a fluid diffusion layer. The membrane is ion conductive (typically proton conductive), and acts both as a barrier for isolating the reactant streams from each other and as an electrical insulator between the two electrodes. A typical commercial PEM is a sulfonated perfluorocarbon membrane sold by E.I. Du Pont de Nemours and Company under the trade designation NAFION®. The electrocatalyst is typically a precious metal composition (e.g., platinum metal black or an alloy thereof) and may be provided on a suitable support (e.g., fine platinum particles supported on a carbon black support).
In a fuel cell, a MEA is typically interposed between two separator plates that are substantially impermeable to the reactant fluid streams. The plates typically act as current collectors and provide support for the MEA. In addition, the plates may have reactant channels formed therein and act as flow field plates providing access for the reactant fluid streams to the respective porous electrodes and providing for the removal of reaction products formed during operation of the fuel cell.
In a fuel cell stack, a plurality of fuel cells are connected together, typically in series, to increase the overall output power of the assembly. In such an arrangement, one side of a given separator plate may serve as an anode flow field plate for one cell and the other side of the plate may serve as the cathode flow field plate for the adjacent cell. In this arrangement, the plates may be referred to as bipolar plates. Typically, a plurality of inlet ports, supply manifolds, exhaust manifolds and outlet ports are utilized to direct the reactant fluid to the reactant channels in the flow field plates. In addition, further inlet ports, supply manifolds, exhaust manifolds and outlets ports are utilized to direct a coolant fluid to interior passages within the fuel cell stack to absorb heat generated by the exothermic reaction in the fuel cells. The supply and exhaust manifolds may be internal manifolds, which extend through aligned openings formed in the flow field plates and MEAs, or may comprise external or edge manifolds, attached to the edges of the flow field plates.
A broad range of reactants can be used in PEM fuel cells. For example, the fuel stream may be substantially pure hydrogen gas, a gaseous hydrogen-containing reformate stream, or methanol in a direct methanol fuel cell. The oxidant may be, for example, substantially pure oxygen or a dilute oxygen stream such as air.
During normal operation of a PEM fuel cell, fuel is electrochemically oxidized on the anode side, typically resulting in the generation of protons, electrons, and possibly other species depending on the fuel employed. The protons are conducted from the reaction sites at which they are generated, through the membrane, to electrochemically react with the oxidant on the cathode side. The electrons travel through an external circuit providing useable power and then react with the protons and oxidant on the cathode side to generate water reaction product.
Fuel cell stacks are often enclosed in a housing which is suitable for isolating the fuel cell stack from the surrounding environment. As a result, in the event of a leak originating from the fuel cell stack, a fuel cell therein, or any of the manifolds or conduits, the leaked fluid (e.g., the hydrogen-rich gas) will accumulate within the volume of the housing. Typically, there are small accumulations of hydrogen in the housing, as hydrogen leaks cannot in most cases be entirely prevented, hydrogen being a permeating gas. However, as the level of hydrogen accumulation increases, the risk of explosions or fire resulting from the resulting mixture of such hydrogen and the oxygen in the housing increases.
German Patent Application DE 100 31 238 discloses a fuel cell system equipped with a ventilated housing, wherein fans, designed so as not to constitute an ignition source, are used as ventilating means. The ventilated housing addresses the potential safety hazard which can be posed by the accumulation of explosive mixtures of hydrogen and oxygen within the fuel cell system environment.
With respect to the use of recombiners with fuel cell systems, U.S. Patent Application Publication No. 2003/0082428 discloses a fuel cell system comprising a housing containing a recombiner and at least one other component of the fuel cell system, wherein the housing is capable of containing leaked fluids originating from a component of the fuel cell system and the recombiner is capable of converting the leaked fluid into a non-explosive mixture. As disclosed, the recombiner comprises a catalyst coating applied to an interior surface of the housing or to an appropriate support material, which is attached to an interior surface of the housing.
In addition, U.S. Patent Application Publication No. 2005/0014037 discloses a fuel cell or fuel cell stack having a recombination catalyst disposed in the hydrogen and/or oxygen distribution system (e.g., flow fields, manifolds, etc. . . . ) of the fuel cell or fuel cell stack. Again, the recombination catalyst is simply applied as a coating to interior surfaces of the hydrogen and/or oxygen distribution system.
German Patent Application DE 10 2004 020 705 discloses a fuel cell comprising an anode, a cathode and a membrane interposed there between for use as a recombiner in a fuel cell system. During operation of the system, hydrogen transferred to the system's coolant loop is first separated from the coolant in a gas separator and then fed to the fuel cell serving as the recombiner where it is recombined with fresh air in a low temperature reaction. Except for such general disclosure, no further details are given about the design of the fuel cell used as the recombiner.
Accordingly, while advances have been made in this field, there remains a need for systems to address potential accumulation of reactive mixtures, such as hydrogen and oxygen mixtures, within a fuel cell stack environment, particularly within a housing enclosing a stack. The present invention fulfills this need and provides further related advantages.
In brief, the present invention is directed to a fuel cell system comprising a flame arresting recombiner. More specifically, the present invention is directed to a fuel cell system comprising a housing having an interior space fluidly containing a fuel cell stack and a flame arresting recombiner.
In one embodiment, a fuel cell system is provided comprising a housing having an interior space fluidly containing a fuel cell stack and a flame arresting recombiner, wherein: (1) the flame arresting recombiner comprises at least one fuel cell having at least one anode supply channel fluidly connecting the fuel cell and the interior space of the housing; and (2) the anode supply channel of the fuel cell of the flame arresting recombiner is configured to prevent flame propagation. In a more specific embodiment, the anode supply channel of the fuel cell of the flame arresting recombiner has a depth less than about 0.6 mm and a length of at least about 3.0 mm.
In a further embodiment, the fuel cell of the flame arresting recombiner comprises: (1) an anode and a cathode; (2) an anode plate having an active surface facing the anode and an oppositely facing non-active surface, wherein a plurality of anode flow field channels are formed on the active surface of the anode plate; and (3) a cathode plate having an active surface facing the cathode and an oppositely facing non-active surface.
In another further embodiment, the fuel cell of the flame arresting recombiner may further comprise a membrane disposed between the anode and the cathode.
In another further embodiment, the anode supply channel of the fuel cell of the flame arresting recombiner is formed on the active surface of the anode plate and is fluidly connected to the anode flow field channels.
In another further embodiment, the anode supply channel of the fuel cell of the flame arresting recombiner comprises: (1) at least one anode supply backfeed channel at least partially formed on the non-active surface of the anode plate and configured to prevent flame propagation; (2) an anode supply backfeed port extending through the anode plate; and (3) an anode supply transition region formed on the active surface of the anode plate of the fuel cell and fluidly connected to the anode flow field channels. In a more specific embodiment, the anode supply backfeed channel has a depth less than about 0.6 mm and a length of at least about 3.0 mm.
In another further embodiment, the fuel cell of the flame arresting recombiner further comprises at least one cathode supply channel. In certain embodiments the cathode supply channel of the fuel cell of the flame arresting recombiner may fluidly connect the fuel cell and an oxidant supply. In other embodiments, the cathode supply channel of the fuel cell of the flame arresting recombiner may fluidly connect the fuel cell and the interior space of the housing, and the cathode supply channel of the fuel cell of the flame arresting recombiner may be configured to prevent flame propagation. In a more specific embodiment, the cathode supply channel of the fuel cell of the flame arresting recombiner may have a depth less than about 0.6 mm and a length of at least about 3.0. mm.
In another further embodiment, the fuel cell of the flame arresting recombiner comprises: (1) an anode and a cathode; (2) an anode plate having an active surface facing the anode and an oppositely facing non-active surface, wherein a plurality of anode flow field channels are formed on the active surface of the anode plate; and (3) a cathode plate having an active surface facing the cathode and an oppositely facing non-active surface, wherein a plurality of cathode flow field channels are formed on the active surface of the cathode plate.
In another further embodiment, the fuel cell of the flame arresting recombiner may further comprise a membrane disposed between the anode and the cathode.
In certain embodiments, the anode supply channel of the fuel cell of the flame arresting recombiner is formed on the active surface of the anode plate and is fluidly connected to the anode flow field channels, and the cathode supply channel of the fuel cell of the flame arresting recombiner is formed on the active surface of the cathode plate and is fluidly connected to the cathode flow field channels.
In other embodiments, the anode supply channel of the fuel cell of the flame arresting recombiner comprises: (a) at least one anode supply backfeed channel at least partially formed on the non-active surface of the anode plate and configured to prevent flame propagation; (b) an anode supply backfeed port extending through the anode plate; and (c) an anode supply transition region formed on the active surface of the anode plate of the fuel cell and fluidly connected to the anode flow field channels, and the cathode supply channel of the fuel cell of the flame arresting recombiner comprises: (a) at least one cathode supply backfeed channel at least partially formed on the non-active surface of the cathode plate and configured to prevent flame propagation; (b) a cathode supply backfeed port extending through the cathode plate; and (c) a cathode supply transition region formed on the active surface of the cathode plate of the fuel cell and fluidly connected to the cathode flow field channels. In more specific embodiments, each of the anode and cathode supply backfeed channels has a depth less than about 0.6 mm and a length of at least about 3.0 mm.
In another embodiment, the fuel cell system further comprises a ventilation inlet line fluidly connected to the housing, and a ventilation outlet line fluidly connected to an outlet of the flame arresting recombiner.
In another embodiment, the fuel cell system further comprises a cooling subsystem capable of cooling the flame arresting recombiner. In a further embodiment, the fuel cell of the flame arresting recombiner comprises: (1) an anode and a cathode; (2) an anode plate having an active surface facing the anode and an oppositely facing non-active surface; and (3) a cathode plate having an active surface facing the cathode and an oppositely facing non-active surface, and the cooling subsystem comprises a plurality of coolant flow field channels formed on the non-active surfaces of the anode and cathode plates of the fuel cell.
In another embodiment, the flame arresting recombiner comprises more than one fuel cell.
In another embodiment, the fuel cell of the flame arresting recombiner comprises more than one anode supply channel.
In a further embodiment, the fuel cell of the flame arresting recombiner comprises: (1) an anode and a cathode; (2) an anode plate having an active surface facing the anode and an oppositely facing non-active surface, wherein a plurality of anode flow field channels are formed on the active surface of the anode plate; and (3) a cathode plate having an active surface facing the cathode and an oppositely facing non-active surface; and each of the anode supply channels is fluidly connected to one of the anode flow field channels. In a more specific embodiment, each of the anode supply channels has a depth less than about 0.6 mm and a length of at least about 3.0 mm.
In another further embodiment, the fuel cell of the flame arresting recombiner further comprises more than one cathode supply channel fluidly connecting the fuel cell and the interior space of the housing, and the cathode supply channels of the fuel cell of the flame arresting recombiner are configured to prevent flame propagation.
In yet a further embodiment, the fuel cell of the flame arresting recombiner comprises: (1) an anode and a cathode; (2) an anode plate having an active surface facing the anode and an oppositely facing non-active surface, wherein a plurality of anode flow field channels are formed on the active surface of the anode plate; and (3) a cathode plate having an active surface facing the cathode and an oppositely facing non-active surface, wherein a plurality of cathode flow field channels are formed on the active surface of the cathode plate; each of the anode supply channels is fluidly connected to one of the anode flow field channels; and each of the cathode supply channels is fluidly connected to one of the cathode flow field channels. In a more specific embodiment, each of the anode and cathode supply channels has a depth less than about 0.6 mm and a length of at least about 3.0 mm.
As one of skill in the art will appreciate, further embodiments may be provided by combining the recited elements from one or more of the foregoing embodiments. These and other aspects of the invention will be evident upon reference to the following detailed description and attached drawings.
In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the art will understand that the invention may be practiced without these details. In other instances, well-known structures associated with fuel cells, fuel cell stacks, and fuel cell systems have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to”.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
As noted above, the present invention provides a fuel cell system comprising a housing for containing leaked fluids originating from a fuel cell stack and a flame arresting recombiner for converting the leaked fluids into a non-explosive mixture or material.
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In conventional recombiners currently employed in fuel cell systems, high temperatures resulting from the recombination of hydrogen and oxygen can cause autoignition of the hydrogen-oxygen fluid mixture, which can lead to dangerous backburning into other components of the fuel cell system. The flame arresting recombiner 130 of the present invention, on the other hand, comprises at least one fuel cell having at least one anode supply channel 132 (not shown in detail in
As one of skill in the art will appreciate, the terms “configured to prevent flame propagation” mean that the aperture through which the burning hydrogen/air mixture enters is narrow enough such that the heat generated by the flame is conducted to the surrounding walls to make the combustion process cease. For example, in more specific embodiments, anode supply channel 132 has a depth less than about 0.6 mm (the flame quench distance for a stoichiometric hydrogen-air mixture) and a length of at least about 3.0 mm.
In addition, as one of skill in the art will appreciate, the terms “fluidly connected” mean that the described elements (e.g., the fuel cell of flame arresting recombiner 130 and interior space 115 of housing 110 of
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As one of skill in the art will appreciate, in embodiments comprising cooling subsystem 150, flame arresting recombiner 130 could be used as a “micro-heating loop” wherein heat from the recombination reaction occurring within flame arresting recombiner 130 may be used to pre-warm coolant in cooling subsystem 150 thereby aiding in the start-up of fuel cell stack 120 from cold or sub-zero temperatures.
Anode plate 240 has at least one anode flow field channel 246 formed on its active surface 242 facing anode 220. Similarly, cathode plate 250 has at least one cathode flow field channel 256 formed on its active surface 252 facing cathode 230. When assembled against the cooperating surfaces of anode and cathode 220 and 230, respectively, anode and cathode flow field channels 246 and 256 form reactant flow field passages to anode 220 and cathode 230, respectively.
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In a flame arresting recombiner comprising more than one fuel cell (for example, a flame arresting recombiner comprising a fuel cell stack), a plurality of fuel cells 200 are arranged in series, such that, with respect to a single fuel cell 200, anode plate 240 is adjacent to the cathode plate 250 of one of the two adjacent fuel cells 200 and cathode plate 250 is adjacent to the anode plate 240 of the other adjacent fuel cell 200 (i.e., anode 220 faces the cathode 230 of one adjacent fuel cell 200 and cathode 230 faces the anode 220 of the other adjacent fuel cell 200).
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Reactant supply channels 520 may fluidly connect reactant flow field channels 510 to a reactant source (such as the interior space 115 of housing 110 in
A 20-cell liquid cooled fuel cell stack, wherein each fuel cell included an anode, a cathode and a polymer electrolyte membrane there between, was used to recombine the hydrogen from an incoming air-hydrogen mixture into water. The stack was placed on a test bench and was not enclosed in a casing. The stack was not connected to a load. A hydrogen/air mixture over a range of 0 to 67% H2 by volume in the input air flow was fed to both the cathode and anode of the recombining stack. The H2 concentration at the stack outlet was measured, as well as the O2 concentration and the temperature rise across the stack at a fixed coolant flow rate (around 2 lpm of water through the coolant channels). Tests were conducted at an air flow of 50 slpm.
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While particular steps, elements, embodiments and applications of the present invention have been shown and described herein for purposes of illustration, it will be understood, of course, that the invention is not limited thereto since modifications may be made by persons skilled in the art, particularly in light of the foregoing teachings, without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
