FUEL CELL SYSTEM CONFIGURED TO OPERATE IN COLD CONDITIONS AND METHOD OF OPERATING THE SAME

A method of operating a fuel cell system includes providing an anode exhaust stream from a stack of fuel cells into an anode exhaust cooler, providing an air inlet stream into the anode exhaust cooler and heating the air inlet stream using heat extracted from the anode exhaust stream, providing a heated air inlet stream output from the anode exhaust cooler into the stack, providing a cooled anode exhaust stream at a temperature between 110° C. and 180° C. from the anode exhaust cooler into an anode recycle blower, and recycling at least a portion of the cooled anode exhaust stream into a fuel inlet stream provided into the stack.

FIELD

Aspects of the present invention relate to fuel cell systems, and more particularly, to fuel cell systems configured to operate in cold conditions.

BACKGROUND

Fuel cells, such as solid oxide fuel cells, are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels or hydrogen containing fuels such as ammonia. There are classes of fuel cells, such as the solid oxide regenerative fuel cells, that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input.

SUMMARY

According to various embodiments, a fuel cell system includes a stack of fuel cells, an anode exhaust cooler configured to heat an air inlet stream using heat extracted from an anode exhaust stream output from the stack, a first air conduit fluidly connected to an air inlet of the anode exhaust cooler and configured to provide an air inlet stream to the anode exhaust cooler, a second air conduit connected to an air outlet of the anode exhaust cooler and configured to receive a heated air inlet stream output from the anode exhaust cooler and to provide the heated air inlet stream into the stack, a first anode exhaust conduit fluidly connecting an anode exhaust outlet of the stack to an anode exhaust inlet of the anode exhaust cooler, a second anode exhaust conduit fluidly connecting an anode exhaust outlet of the anode exhaust cooler to a fuel inlet of the stack, and at least one component configured to maintain a temperature of an anode exhaust stream exiting the anode exhaust cooler into the second anode exhaust conduit at a temperature above 100° C.

According to various embodiments, a method of operating a fuel cell system includes providing an anode exhaust stream from a stack of fuel cells into an anode exhaust cooler, providing an air inlet stream into the anode exhaust cooler and heating the air inlet stream using heat extracted from the anode exhaust stream, providing a heated air inlet stream output from the anode exhaust cooler into the stack, providing a cooled anode exhaust stream at a temperature between 110° C. and 180° C. from the anode exhaust cooler into an anode recycle blower, and recycling at least a portion of the cooled anode exhaust stream into a fuel inlet stream provided into the stack.

DETAILED DESCRIPTION

FIG.1is a schematic representation of a SOFC system10, according to various embodiments of the present disclosure. Referring toFIG.1, the system10includes a hotbox100and various components disposed therein or adjacent thereto. The hot box100may contain fuel cell stacks102, such as a solid oxide fuel cell stacks containing alternating fuel cells and interconnects. One solid oxide fuel cell of the stack contains a ceramic electrolyte, such as yttria stabilized zirconia (YSZ), scandia stabilized zirconia (SSZ), scandia and ceria stabilized zirconia or scandia, yttria and ceria stabilized zirconia, an anode electrode, such as a nickel-YSZ, a nickel-SSZ or nickel-doped ceria cermet, and a cathode electrode, such as lanthanum strontium manganite (LSM). The interconnects may be metal alloy interconnects, such as chromium-iron alloy interconnects. The stacks102may be arranged over each other to create a single column with a plurality of columns contained in a single hot box, or each stack may comprise one large column with multiple columns contained in a single hot box.

The hot box100may also contain an anode recuperator heat exchanger110, a cathode recuperator heat exchanger120, an anode tail gas oxidizer (ATO)150, an anode exhaust cooler heat exchanger140, a splitter160, and a vortex generator162. The system10may also include a catalytic partial oxidation (CPOx) reactor200, a mixer210, a CPOx blower204(e.g., air blower), a system blower208(e.g., air blower), and an anode recycle blower212, which may be disposed outside of the hotbox100. However, the present disclosure is not limited to any particular location for each of the components with respect to the hotbox100.

The CPOx reactor200receives a fuel inlet stream from a fuel inlet300, through fuel conduit300A. The fuel inlet300may be a fuel tank or a utility natural gas line including a valve to control an amount of fuel provided to the CPOx reactor200. The CPOx blower204may provide air to the CPOx reactor202during system start-up. The fuel and/or air may be provided to the mixer210by fuel conduit300B. Fuel flows from the mixer210to the anode recuperator110through fuel conduit300C. The fuel is heated in the anode recuperator110by a portion of the fuel exhaust supplied by conduit308A and the fuel then flows from the anode recuperator110to the stacks102through fuel conduit300D.

The system blower208may be configured to provide an air stream (e.g., air inlet stream) to the anode exhaust cooler140through air conduit302A. Air flows from the anode exhaust cooler140to the cathode recuperator120through air conduit302B. The air is heated by the ATO exhaust in the cathode recuperator120. The air flows from the cathode recuperator120to the stacks102through air conduit302C.

An anode exhaust stream (e.g., the fuel exhaust stream described below with respect toFIGS.3A-3C) generated in the stacks102is provided to the anode recuperator110through anode exhaust conduit308A. The anode exhaust may contain unreacted fuel and may also be referred to herein as fuel exhaust. The anode exhaust may be provided from the anode recuperator110to the splitter160by anode exhaust conduit308B. A first portion of the anode exhaust may be provided from the splitter160to the anode exhaust cooler140through the anode exhaust conduit308C. A second portion of the anode exhaust may be provided from the splitter160to the ATO150through the anode exhaust conduit308D. The first portion of the anode exhaust heats the air inlet stream in the anode exhaust cooler140and may then be provided from the anode exhaust cooler140to the mixer210through the anode exhaust conduit308E. The anode recycle blower212may be configured to move anode exhaust though anode exhaust conduit308E.

Cathode exhaust generated in the stacks102flows to the ATO150through cathode exhaust conduit304A. The vortex generator162may be disposed in the exhaust conduit304A and may be configured to swirl the cathode exhaust. The anode exhaust conduit308D may be fluidly connected to the vortex generator162or to the cathode exhaust conduit304A or the ATO150downstream of the vortex generator162. The swirled cathode exhaust may mix with the second portion of the anode exhaust provided by the splitter160before being provided to the ATO150. The mixture may be oxidized in the ATO150to generate an ATO exhaust. The ATO exhaust flows from the ATO150to the cathode recuperator120through the cathode exhaust conduit304B. Exhaust flows from the cathode recuperator and out of the hotbox100through cathode exhaust conduit304C.

An optional water injector (not shown) may be provided on the anode exhaust conduit308C. The water injector may comprise a nozzle or pipe connected to a water source (e.g., water tank or municipal water supply pipe). The injector injects the water into the anode exhaust stream, where the water is vaporized and converted to steam. Alternatively or in addition, a steam generator (not shown inFIG.1) may be located in the hot box to provide steam into the mixer210. The steam generator may comprise one or more water pipes located in the path of the cathode exhaust stream, such that the cathode exhaust stream exiting the cathode recuperator120via conduit304C vaporizes the water in the one or more water pipes.

The system10may further contain a system controller225configured to control various elements of the system10. The controller225may include a central processing unit configured to execute stored instructions. For example, the controller225may be configured to control fuel and/or air flow through the system10, according to fuel composition data.

FIG.2Ais a sectional view showing components of the hot box100of the system10ofFIG.1, andFIG.2Bshows an enlarged portion ofFIG.2A.FIG.2Cis a three-dimensional cut-away view of a central column400of the system10, according to various embodiments of the present disclosure, andFIG.2Dis a perspective view of an anode hub structure600disposed in a hot box base101on which the column400may be disposed.

Referring toFIGS.2A-2D, the fuel cell stacks102may be disposed around the central column400in the hot box100. For example, the stacks102may be disposed in a ring configuration around the central column400and may be positioned on the hot box base101. The column400may include the anode recuperator110, the ATO150, and the anode exhaust cooler140. In particular, the anode recuperator110is disposed radially inward of the ATO150, and the anode exhaust cooler140is mounted over the anode recuperator110and the ATO150. In one embodiment, an oxidation catalyst112and/or the hydrogenation catalyst114may be located in the anode recuperator110(seeFIG.1). A reforming catalyst116may also be located at the bottom of the anode recuperator110as a steam methane reformation (SMR) insert. The ATO150may include an oxidation catalyst.

The anode hub structure600may be positioned under the anode recuperator110and ATO150and over the hot box base101. The anode hub structure600is covered by an ATO skirt1603. The vortex generator162and fuel exhaust splitter160are located over the anode recuperator110and ATO150and below the anode exhaust cooler140. An ATO glow plug1602, which initiates the oxidation of the stack fuel exhaust in the ATO during startup, may be located near the bottom of the ATO150.

The anode hub structure600is used to distribute fuel evenly from the central column to fuel cell stacks102disposed around the central column400. The anode flow hub structure600includes a grooved cast base602and a “spider” hub of fuel inlet conduits300D and outlet conduits308A. Each pair of conduits300D,308A connects to a fuel cell stack102. Anode side cylinders (e.g., anode recuperator110inner and outer cylinders and ATO150outer cylinder) are then welded or brazed into the grooves in the base602, creating a uniform volume cross section for flow distribution as discussed below.

A lift base1604is located under the hot box base101, as illustrated inFIG.2C. In an embodiment, the lift base1604includes two hollow arms with which the forks of a forklift can be inserted to lift and move the system, such as to remove the system from a cabinet (not shown) for repair or servicing.

As shown by the arrows inFIGS.2A and2B, air enters the top of the hot box100and flows through the anode exhaust cooler140where it is heated by anode exhaust and then flows into the cathode recuperator120where it is heated by ATO exhaust (not shown) from the ATO150. The heated air then flows inside the cathode recuperator120through a first vent or opening121. The air then flows through the stacks102and reacts with fuel (i.e., fuel inlet stream) provided from the anode hub structure600. Air exhaust flows from the stacks102, through a second vent or opening123. The air exhaust then passes through vanes of the vortex generator162and is swirled before entering the ATO150.

The splitter160may direct the second portion of the fuel exhaust exiting the top of the anode recuperator100through openings (e.g., slits) in the splitter into the swirled air exhaust (e.g., in the vortex generator162or downstream of the vortex generator in the cathode exhaust conduit304A or in the ATO150). At such the fuel and air exhaust may be mixed before entering the ATO150.

FIGS.3A and3Bare side cross-sectional views showing flow distribution through the central column400, and3C is a partial perspective view taken through the anode recuperator110. Referring toFIGS.2A,2B,3A, and3C, the anode recuperator110includes an inner cylinder110A, a corrugated plate110B, and an outer cylinder110C. Fuel from fuel conduit300C enters the top of the central column400. The fuel then bypasses the anode exhaust cooler140by flowing through its hollow core and then flows through the anode recuperator110, between the outer cylinder110C and the and the corrugated plate110B. The fuel then flows through the hub base602and conduits300D of the anode hub structure600shown inFIG.3B, to the stacks102.

Referring toFIGS.2A,2B,2C,3A, and3B, the fuel exhaust flows from the stacks102through conduits308A into the hub base602, and from the hub base602through the anode recuperator110, between in inner cylinder110A and the corrugated plate110B, and through conduit308B into the splitter160. A first portion of the fuel exhaust may flow from the splitter160to the anode exhaust cooler140through conduit308C, while a second portion may flow from the splitter160to the ATO150through conduit308D, as shown inFIG.1. The relative amounts of anode exhaust provided to the ATO150and the anode exhaust cooler140is controlled by the anode recycle blower212. The higher the blower212speed, the larger portion of the anode exhaust is provided into conduit308C and a smaller portion of the anode exhaust is provided to the ATO150via conduit308D, and vice-versa. Anode exhaust cooler inner core insulation140A may be located between the fuel conduit300C and bellows852/supporting cylinder852A located between the anode exhaust cooler140and the vortex generator162, as shown inFIG.3A. This insulation minimizes heat transfer and loss from the first portion of the anode exhaust stream in conduit308C on the way to the anode exhaust cooler140. Insulation140A may also be located between conduit300C and the anode exhaust cooler140to avoid heat transfer between the fuel inlet stream in conduit300C and the streams in the anode exhaust cooler140. In other embodiments, insulation140A may be omitted from inside the cylindrical anode exhaust cooler140.

FIG.3Balso shows air flowing from the air conduit302A to the anode exhaust cooler140(where it is heated by the first portion of the anode exhaust) and then from the anode exhaust cooler140through conduit302B to the cathode recuperator120. The first portion of the anode exhaust is cooled in the anode exhaust cooler140by the air flowing through the anode exhaust cooler140. The cooled first portion of the anode exhaust is then provided from the anode exhaust cooler140to the anode recycle blower212shown inFIG.1.

The anode exhaust provided to the ATO150is not cooled in the anode exhaust cooler140. This allows higher temperature anode exhaust to be provided into the ATO150than if the anode exhaust were provided after flowing through the anode exhaust cooler140. For example, the anode exhaust provided into the ATO150from the splitter160may have a temperature of above 350° C., such as from about 350 to about 500° C., for example, from about 375 to about 425° C., or from about 390 to about 410° C. Furthermore, since a smaller amount of anode exhaust is provided into the anode exhaust cooler140(e.g., not 100% of the anode exhaust is provided into the anode exhaust cooler due to the splitting of the anode exhaust in splitter160), the heat exchange area of the anode exhaust cooler140may be reduced. The anode exhaust provided to the ATO150may be oxidized by the stack cathode exhaust (i.e., air) and provided to the cathode recuperator120through the cathode exhaust conduit304B.

Cold Weather Configurations

Fuel cell systems are typically rated for operation in ambient air temperatures of about −20° C. or greater. Designing fuel cell systems, such as solid oxide fuel cell (SOFC) systems to work in extreme cold weather conditions (e.g., ambient temperatures less than negative 20° C.) is a challenging task both for outdoor rated as well as indoor rated systems, and particularly for systems that use high volumes of air flow. Conventionally, warming incoming air using one or more heaters to a desired temperature range may require a large amount of energy, which decreases the overall efficiency of the system. In some systems, it may not be possible to add localized heaters to certain components, for example motor bearings, and utilizing components designed for extremely low temperatures may be cost and/or size prohibitive.

In view of such problems, various embodiments provide fuel cell systems that utilize heat generated by exothermic fuel cell reactions to heat incoming ambient air to a desired operating temperature. Various embodiments provide improved efficiency for cold weather operation, as compared to conventional systems. These embodiments provide modifications and components to the fuel cell systems for operation in cold conditions, such as cold weather conditions in ambient air temperatures of less than −20° C., such as −21° C. to −40° C.

In cold weather conditions, the ambient air provided to the anode exhaust cooler140may excessively cool the anode exhaust stream, which may cause undesirable water condensation in the anode exhaust stream. Specifically, in the embodiments of the present disclosure, the temperature of the anode exhaust stream exiting the anode exhaust cooler140is maintained above about 100° C., such as a temperature of above about 105° C. For example, the anode exhaust may be output from the anode exhaust cooler140at a temperature ranging from about 110° C. to about 180° C., such as from about 110° C. to about 120° C., when ambient air temperatures are below −20° C. Therefore, water vapor in the anode exhaust is maintained above the water boiling temperature to prevent water condensation in the anode exhaust. Furthermore, the anode exhaust may be maintained below the maximum operating temperature rating of the anode exhaust blower212to prevent damage to the anode exhaust blower212. For example, if the anode exhaust blower is rated for a maximum operating temperature of 200° C., then the temperature of the anode exhaust entering the anode exhaust blower212from the anode exhaust cooler140may be maintained at 180° C. or less. Therefore, water condensation (and potential water freezing in the pipes at extreme cold temperatures) is avoided without damaging the anode exhaust blower212.

FIG.4Ais a partial perspective view showing fuel exhaust stream410and air inlet stream412flowing through an anode exhaust cooler140ofFIG.1, andFIG.4Bis a partial cross-sectional view of cold weather operation components that may be included in the system10ofFIG.1, according to various embodiments of the present disclosure. In the embodiment shown inFIG.4B, the system10may include the optional water evaporator402which includes coiled water pipes404which are heated by the cathode exhaust stream exiting the cathode recuperator120. Alternatively, the evaporator402may be omitted if a water injector is provided on the anode exhaust conduit308C.

Referring toFIGS.1,4A, and4B, the anode exhaust cooler140may include an inner cylinder140A, a corrugated plate140B, and an outer cylinder140C. Fuel exhaust from fuel exhaust conduit308C flows into the bottom of the anode exhaust cooler140and along a first side of the corrugated plate140B. The air inlet stream from air conduit302A enters the top of the anode exhaust cooler140and flows along an opposing second side of the corrugated plate140B. A shroud142may be disposed around the anode exhaust cooler140and may be configured to provide air received from the air conduit302A to the anode exhaust cooler140. For example, the shroud142may be a cylinder that surrounds at least a top portion of the anode exhaust cooler140. A bypass air conduit302D may fluidly connect the shroud142to the air conduit302B. A bypass valve305may be disposed in the bypass air conduit302D.

Accordingly, a portion412B of the air inlet stream412provided to the shroud142may be diverted into the bypass air conduit302D and may be provided to the air conduit302B, without passing through the anode exhaust cooler140. In particular, the air inlet stream412flowing into the shroud142may be divided into a first air stream412A that flows into the anode exhaust cooler140and exchanges heat with the anode exhaust stream, and a second (i.e., bypass) air stream412B that flows from the shroud142and directly into the air conduit302B, via the bypass air conduit302D.

The controller225may be configured to control the bypass valve305according to the temperature of the air in the air conduit302A, which may be detected by a temperature sensor309. For example, the controller225may be configured to provide a higher air flow rate (e.g., a higher air mass flow) through the bypass air conduit302D, in order to prevent excessive cooling of the anode exhaust, due to low ambient air temperatures of the air flowing through the air conduit302A. In some embodiments, the controller225may be configured to control the bypass valve305, such that the temperature of anode exhaust exiting the anode exhaust cooler140remains above about 100° C., such as at a temperature of 110° C. to 180° C., such when ambient air temperatures are below −20° C. As such, the system10may be configured to prevent water condensation in the anode exhaust when the system10is subjected to extremely cold ambient air, such as ambient air having a temperature of less than −20° C. In other words, if the air inlet stream flowing through the air conduit302A is determined to be too cold, then the bypass valve305is opened (or opened wider than before) to provide at least a part of the air inlet stream (or a greater part of the air inlet stream) directly into the air conduit302B bypassing the anode exhaust cooler140. Thus, the anode exhaust stream in the anode exhaust cooler140is cooled to a lesser degree than when the bypass valve305is closed (i.e., fully or partially closed). In contrast, if the controller225determines that the air inlet temperature is relatively high (e.g., at −20° C. or higher, such as a 0 to 25° C., then the bypass valve305may be closed or narrowed to provide additional cooling to the anode exhaust stream to maintain it below the rated temperature of the anode exhaust blower212to prevent damage to the blower.

In some embodiments, the system10may include multiple bypass air conduits302D connecting the shroud142to the air conduit302B, and additional bypass valves305to control air flow through each bypass air conduit302D. In other embodiments, multiple bypass air conduits302D may be controlled by a single bypass valve305. In the case of multiple bypass valves305, there may be modes of operation where the multiple valves are operated the same way (e.g., all opened or all closed) and modes of operation where the multiple valves are not operated the same way (e.g., some closed and some opened, or multiple valves configured with different degrees of partial openness).

FIGS.5A and5Bare partial cross-sectional views of modified cold weather operation components that may be included in the system10ofFIG.1, according to alternative embodiments of the present disclosure.

Referring toFIG.5A, the bypass air conduit302D may fluidly connect the air conduit302A to the air conduit302B, thereby bypassing both the anode exhaust cooler140and the shroud142. An additional air control valve307may optionally be disposed in the air conduit302A downstream of the bypass conduit302D. The air control valve307may be configured to control the air inlet stream flow into the shroud142and the anode exhaust cooler140. In some embodiments, the valve307may be actuated to force additional air into the bypass air conduit302D, in order to prevent water condensation from the anode exhaust in the bypass air conduit302D.

In this embodiment, if the air inlet stream flowing through the air conduit302A is determined to be too cold, then the bypass valve305is opened (or opened wider than before), while the air control valve307is fully or partially closed to provide at least a part of the air inlet stream (or a greater part of the air inlet stream or all of the air inlet stream) directly into the air conduit302B bypassing the anode exhaust cooler140. Thus, the anode exhaust stream in the anode exhaust cooler140is cooled to a lesser degree than when the bypass valve305is closed and the air control valve307is opened. In contrast, if the controller225determines that the air inlet temperature is relatively high (e.g., at −20° C. or higher, such as a 0 to 25° C., then the bypass valve305may be fully or partially closed while the air control valve307is fully or partially opened wider to provide additional cooling to the anode exhaust stream to maintain it below the rated temperature of the anode exhaust blower212to prevent damage to the blower.

In an alternative embodiment illustrated inFIG.5B, instead of including the bypass conduit302D, the shroud142is split into an upper portion142A and lower portion142B by a horizontal shroud plate142P. The lower portion142B of the shroud142functions as the bypass conduit (i.e., performs a similar function to conduit302D described above). Specifically, the bypass valve305may be located in the shroud plate142P, while the air control valve may be located in the upper portion142A of the shroud142. The anode exhaust cooler140may include an upper portion140C surrounded by the upper portion142A of the shroud142and a lower portion140D surrounded by the lower portion142B of the shroud142. The periphery of the anode exhaust cooler140is surrounded by a cylindrical baffle plate140E. The baffle plate140E includes an upper air inlet opening140F located above the shroud plate140P between the upper portion140C of the anode exhaust cooler140and the upper portion142A of the shroud142. The baffle plate140E also includes lower air inlet opening140G located below upper air inlet opening140F and below the shroud plate142P between the lower portion140D of the anode exhaust cooler140and the lower portion142B of the shroud142.

In this embodiment, if the air inlet stream flowing through the air conduit302A is determined to be too cold, then the bypass valve305is opened (or opened wider than before), while the air control valve307is fully or partially closed to provide at least a portion412B of the air inlet stream412(or a greater part of the air inlet stream or all of the air inlet stream) into the lower portion140D of the anode exhaust cooler140through the lower air inlet opening140G and the lower portion412B of the shroud412. In this embodiment, at least the portion412B of the air inlet stream412bypasses the upper portion140C of the anode exhaust cooler140. Thus, the anode exhaust stream in the anode exhaust cooler140is cooled to a lesser degree than when the bypass valve305is closed and the air control valve307is opened because the anode exhaust stream and at least the second portion412B of the air inlet stream412flow past each other in the anode exhaust cooler140along a shorter path for a shorter period of time.

In contrast, if the controller225determines that the air inlet temperature is relatively high (e.g., at −20° C. or higher, such as a 0 to 25° C.), then the bypass valve305may be fully or partially closed while the air control valve307is fully or partially opened wider to provide all or a larger portion412A of the air inlet stream412into the upper portion140C of the anode exhaust cooler140through the upper inlet opening140F and the upper portion412A of the shroud412. Thus, additional cooling is provided to the anode exhaust stream to maintain it below the rated temperature of the anode exhaust blower212to prevent damage to the blower, since the anode exhaust stream and at least the first portion412A of the air inlet stream412flow past each other in the anode exhaust cooler140along a longer path for a longer period of time.

FIG.6is a schematic view of a fuel cell system12, according to another embodiment of the present disclosure. The fuel cell system12may be similar to the fuel cell system10ofFIG.1. As such, only the differences therebetween will be discussed in detail.

Referring toFIG.6, the system12may include an exhaust heat exchanger170, an optional exhaust valve303, and a system exhaust conduit or chimney330. The exhaust heat exchanger170may be configured to preheat air in the air conduit302A by extracting heat from cathode exhaust output via the cathode exhaust conduit304C from the hotbox100. In particular, the exhaust valve303may divert all or a portion of the cathode exhaust from the cathode exhaust conduit304C into the system exhaust conduit330, which may provide all or a portion of the warm the cathode exhaust to the heat exchanger170. In some embodiments, the heat exchanger170and/or system exhaust conduit330may be fluidly connected to multiple hotboxes100.

The exhaust valve303may be a two-way valve or a proportional valve configured to selectively control an amount of cathode exhaust that is provided to the heat exchanger170. Cathode exhaust remaining in the cathode exhaust conduit304C may be provided to the system exhaust conduit330or may be separately vented from the system12. In particular, the controller225may be configured to control the exhaust valve303according to the temperature of the air in the air conduit302A, or the anode exhaust temperature in the anode exhaust conduit308E. For example, the controller225may be configured to provide a higher cathode exhaust flow rate (e.g., a higher exhaust mass flow) to the heat exchanger170by opening or opening wider the exhaust valve303, in order to heat the air inlet stream in the air conduit302A to compensate for lower ambient air temperatures. Alternatively, the controller225may be configured to fully or partially close the exhaust valve303, such that no cathode exhaust or less cathode exhaust is diverted from the cathode exhaust conduit304C to the heat exchanger170, when ambient air temperatures are high enough that no additional air inlet stream heating is required.

FIG.7Ais a schematic view of a fuel cell system14, according to various embodiments of the present disclosure, andFIG.7Bis a partial cross-sectional view showing exemplary components of system14ofFIG.7A. The fuel cell system14may be similar to the fuel cell system12ofFIG.6. As such, only the differences therebetween will be discussed in detail.

Referring toFIGS.7A and7B, the system14may include a cathode exhaust diversion conduit304E and an exhaust valve311. The diversion conduit304E may be configured to provide at least some of the cathode exhaust stream414flowing out of the cathode recuperator120(e.g., through the cathode exhaust conduit304C) into the air conduit302A. As such, the warm cathode exhaust may mix with the incoming cold air inlet stream412, thereby increasing the temperature of the air provided to the anode exhaust cooler140. Therefore, excessive cooling of anode exhaust in the anode exhaust cooler140may be prevented, which may improve overall system efficiency.

As shown inFIGS.7A and7B, the diversion conduit304F may be fluidly connected to the air conduit302A upstream of the air blower208. In an alternative configuration, the diversion conduit304E may be fluidly connected to the air conduit302A, downstream of the air blower208, as shown by the dashed arrow inFIG.7A. In the alternative configuration, a device, such as an additional blower, may be added to increase the pressure on the diversion conduit304E. Alternatively, the cold air in the air conduit302A may pass through a venturi located on the air conduit302A and suck in the hot cathode exhaust from the diversion conduit304E.

The exhaust valve311may be configured to control exhaust flow through the diversion conduit304E or304F. In particular, the controller225may be configured to control the exhaust valve311, based on the temperature of ambient air supplied to the air conduit302A. For example, the controller225may be configured to provide higher exhaust flow rates at lower ambient air temperatures, in order to heat the ambient air to a desired temperature, such as a temperature ranging from about 0° C. to about 20° C., such as a temperature ranging from about 5° C. to about 15° C., or about 10° C.

FIG.8is a schematic view of a fuel cell system16, according to various embodiments of the present disclosure. The fuel cell system16may be similar to the fuel cell system10ofFIG.1. As such, only the differences therebetween will be discussed in detail.

Referring toFIG.8, the system16may include an anode recycle heat exchanger180, an ATO feed valve313located on an anode exhaust conduit308G, and an anode exhaust export valve315located on an anode exhaust export conduit308F. The anode recuperator110may be fluidly connected to the anode exhaust cooler140by anode exhaust conduit308C, and the splitter160ofFIG.1may be omitted. The anode exhaust cooler140may be fluidly connected to the anode exhaust heat exchanger180and the mixer210by the anode exhaust conduit308E. The anode exhaust conduit308E may be fluidly connected to the vortex generator162by the anode exhaust conduit308G and may also be fluidly connected to anode exhaust export conduit308F.

The anode exhaust conduit308G fluidly connects the anode exhaust conduit308E to the ATO150. The ATO feed valve313may be configured to control the anode exhaust flow through the anode exhaust conduit308G from the anode exhaust conduit308E to the ATO150. The export valve315may control anode exhaust flow through the export conduit308F. In particular, during system startup, the ATO feed valve313may be opened such that at least a portion of the anode exhaust is provided to the ATO150via the anode exhaust conduit308G, and the export valve315may be closed. In addition, the air control valve307may be closed and the bypass valve305may be opened to provide air into the air bypass conduit302D to bypass the anode exhaust cooler140, in order to prevent excessive cooling of the anode exhaust during system startup.

During steady-state operation of the system, the ATO feed valve313may be closed such that the anode exhaust is provided to the mixer210via the anode exhaust conduit308E, after passing through the anode recycle heat exchanger180. In particular, the anode recycle heat exchanger180may be configured to maintain the anode exhaust to a temperature between 110° C. and 180° C., in order to prevent the condensation of water from the anode exhaust as well as to prevent damage to the anode exhaust recycle blower212. In some embodiments, the anode recycle heat exchanger180may be a passive finned tube heat exchanger configured to receive air flowing through a system cabinet containing the hot box100and various system components disposed outside of the hotbox100. For example, the anode recycle heat exchanger180may be positioned near the air intake of the cabinet. In another embodiment, the anode recycle heat exchanger180may be an active finned tube heat exchanger located adjacent to a fan which blows cabinet air onto the anode recycle heat exchanger180. In some embodiments, air conduit302D may be used to bypass the anode exhaust cooler140, in order to prevent water condensation in the anode exhaust due to excessive cooling of the anode exhaust in the anode exhaust cooler140. For example, the anode exhaust cooler140may be at least partially bypassed if the system16is provided with ambient air having a temperature of about 0° C. or less.

Furthermore, during the steady-state system operation, the export valve315may be opened after the ATO feed valve313is closed to divert at least a portion of the anode exhaust from the anode exhaust export conduit308F and out of the system16. For example, the export conduit308F may be fluidly connected to an external anode exhaust processor (e.g., a combined heat and power (CHP) generation assembly) or a containment vessel. If the export valve315is closed, the ATO feed valve313may be opened to divert at least a portion of the anode exhaust to the ATO150. During the opening and closing of the valves313,315, both valves313,315may remain open for one or more seconds in order to prevent deadheading (e.g., anode exhaust flow disruption).

According to various embodiments illustrated inFIGS.1and4B-8, a fuel cell system (10,12,14, and16) includes a stack102of fuel cells, an anode exhaust cooler140configured to heat an air inlet stream using heat extracted from an anode exhaust stream output from the stack102, a first air conduit302A fluidly connected to an air inlet of the anode exhaust cooler140and configured to provide an air inlet stream to the anode exhaust cooler140, a second air conduit302B connected to an air outlet of the anode exhaust cooler140and configured to receive a heated air inlet stream output from the anode exhaust cooler140and to provide the heated air inlet stream into the stack102(e.g., directly or via the cathode recuperator120), a first anode exhaust conduit308C (e.g., alone or in combination with combination with conduits308A and308B) fluidly connecting an anode exhaust outlet of the stack102to an anode exhaust inlet of the anode exhaust cooler140, a second anode exhaust conduit308fluidly connecting an anode exhaust outlet of the anode exhaust cooler140to a fuel inlet of the stack102(e.g., directly or via mixer210and fuel conduits300C and300D), and at least one component configured to maintain a temperature of an anode exhaust stream exiting the anode exhaust cooler140into the second anode exhaust conduit308E at a temperature above 100° C.

In some embodiments, an anode recycle blower212is located on the second anode exhaust stream conduit308E, and the at least one component is configured to maintain the temperature of the anode exhaust stream exiting the anode exhaust cooler140into the second anode exhaust conduit308E at a temperature between 110° C. and 180° C. to prevent water condensation and damage to the blower212.

In the embodiment ofFIGS.1,4B and5A, the at least one component comprises a bypass air conduit302D fluidly connecting the first air conduit302A and the second air conduit302B and bypassing the anode exhaust cooler140, and a bypass valve305configured to control the air inlet stream flow through the bypass air conduit302D. In the embodiments illustrated inFIGS.4B and5A, a shroud142surrounds the anode exhaust cooler140and fluidly connects the first air conduit302A to the air inlet of the anode exhaust cooler140. The bypass air conduit302D directly connects either the shroud412or the first air conduit302A to the second air conduit302B inFIGS.5A and4B, respectively.

In the embodiment ofFIG.5B, the at least one component comprises the shroud412surrounding the anode exhaust cooler140. The shroud412has an upper portion412A fluidly connecting the first air conduit302A to the air inlet140F of the anode exhaust cooler140located in an upper portion140C of the anode exhaust cooler140, and a lower portion412B fluidly connecting the first air conduit302A to a lower air inlet140G of the anode exhaust cooler140located in a lower portion140D of the anode exhaust cooler140.

In the embodiment ofFIG.6, the at least one component comprises the heat exchanger170fluidly connected to the first air conduit302A and the cathode exhaust conduit304C and configured to preheat the air inlet stream in the first air conduit by extracting heat from a cathode exhaust stream output from the stack102. As noted above, the cathode exhaust conduit304is fluidly connected to a cathode exhaust outlet of the stack102(e.g., directly or via the cathode recuperator120).

In the embodiment ofFIGS.7A and7B, the at least one component comprises a cathode exhaust diversion conduit304E or304F fluidly connecting the cathode exhaust conduit304C to the first air conduit302A. The cathode exhaust conduit304is fluidly connected to a cathode exhaust outlet of the stack102(e.g., directly or via the cathode recuperator120).

In the embodiment ofFIG.8, the at least one component may include the anode recycle heat exchanger180and/or the bypass air conduit302D, which may be used to prevent water from condensing out of the anode exhaust and/or damage to the anode recycle blower212.

In the embodiments ofFIGS.1and4B-8, a method of operating a fuel cell system (10,12,14, and16) includes providing an anode exhaust stream from a stack102of fuel cells into an anode exhaust cooler140, providing an air inlet stream412into the anode exhaust cooler140and heating the air inlet stream using heat extracted from the anode exhaust stream, providing a heated air inlet stream output from the anode exhaust cooler140into the stack102, providing a cooled anode exhaust stream at a temperature between 110° C. and 180° C. from the anode exhaust cooler140into an anode recycle blower212, and recycling at least a portion of the cooled anode exhaust stream into a fuel inlet stream provided into the stack102.

In one embodiment, the fuel cell system (10,12,14,16) is operated in an air temperature of less than negative 20° C., such as between negative 21° C. and negative 40° C.

In the embodiments ofFIGS.1,4B,5A and5B, at least a portion of the air inlet stream bypasses the anode exhaust cooler140prior to being provided into the stack102in order to provide the cooled anode exhaust stream at the temperature between 110° C. and 180° C. from the anode exhaust cooler140into the anode recycle blower102.

In the embodiment ofFIG.4B, the at least the portion of the air inlet stream bypasses the anode exhaust cooler140from a shroud142surrounding the anode exhaust cooler140. In the embodiment ofFIG.5A, the at least a portion of the air inlet stream may bypass the anode exhaust cooler140from the first air conduit302A into the second air conduit302B without entering the shroud142.

In the embodiment ofFIG.5B, a first portion412A of the air inlet stream412from an upper portion142A of the shroud142surrounding the anode exhaust cooler140is provided into an upper portion140C of the anode exhaust cooler140. A second portion412B of the air inlet stream412is provided from a lower portion142B of the shroud142into a lower portion140D of the anode exhaust cooler140in order to provide the cooled anode exhaust stream at the temperature between 110° C. and 180° C. from the anode exhaust cooler140into the anode recycle blower212.

In the embodiment ofFIGS.7A and7B, at least a portion of a cathode exhaust stream from the stack102is provided into the air inlet stream412in order to provide the cooled anode exhaust stream at the temperature between 110° C. and 180° C. from the anode exhaust cooler140into the anode recycle blower212.

In the embodiment ofFIG.6, at least a portion of the air inlet stream412is provided into a heat exchanger170upstream of the anode exhaust cooler140, and at least a portion of a cathode exhaust stream is provided from the stack102into the heat exchanger170to heat the air inlet stream in order to provide the cooled anode exhaust stream at the temperature between 110° C. and 180° C. from the anode exhaust cooler140into the anode recycle blower212.