Fuel cell system including anode exhaust diversion and method of operating same

Abstract

To provide a method of operating a fuel cell system.SOLUTION: The method of operating a fuel cell system comprises: providing fuel and air to a stack (102) of fuel cells located in a hotbox (100); operating the stack to generate anode exhaust and cathode exhaust; in a startup mode, providing a first amount of the anode exhaust and the cathode exhaust to an anode tail gas oxidizer (130) located in the hotbox to oxidize the anode exhaust and to generate heat to be provided to the stack; and, in a steady-state mode, stopping providing the anode exhaust to the anode tail gas oxidizer (130) or providing the anode tail gas oxidizer (130) with a second amount of the anode exhaust which is less than the first amount, and providing the anode exhaust and the cathode exhaust to an outside of the hotbox (100).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Aspects of the invention relate to fuel cell systems and methods, and more particularly to fuel cell systems that include anode exhaust diversion elements. [Background technology]

[0002] Fuel cells, such as solid oxide fuel cells, are electrochemical devices that can convert energy stored in a fuel into electrical energy with high efficiency. High-temperature fuel cells include solid oxide fuel cells and molten carbonate fuel cells. These fuel cells can operate using hydrogen and / or hydrocarbon fuels. There are classes of fuel cells, such as solid oxide regenerative fuel cells, that also allow for reverse operation, such that oxidized fuel can be re-reduced to unoxidized fuel using electrical energy as an input. Summary of the Invention

[0003] According to various embodiments, a fuel cell system includes a stack of fuel cells, an anode tail gas oxidizer (ATO) configured to oxidize anode exhaust output from the stack, an exhaust conduit configured to output the anode exhaust from the fuel cell system, a bypass conduit configured to divert the anode exhaust output from the stack to the exhaust conduit, a bypass valve configured to control anode exhaust flow through the bypass conduit, and an ATO conduit configured to supply the anode exhaust to the anode tail gas oxidizer.

[0004] According to various embodiments, a method of operating a fuel cell system includes supplying fuel and air to a stack of fuel cells located within a hot box, operating the stack to generate an anode exhaust and a cathode exhaust, and in a start-up mode, supplying a first amount of the anode exhaust and the cathode exhaust to an anode tail gas oxidizer (ATO) located within the hot box to oxidize the anode exhaust and generate heat that is supplied to the stack, and in a steady-state mode, stopping the supply of the anode exhaust to the anode tail gas oxidizer or supplying a second amount of the anode exhaust to the anode tail gas oxidizer that is less than the first amount, while supplying the anode exhaust and the cathode exhaust outside the hot box.

[0005] According to various embodiments, a method of operating a fuel cell system includes supplying fuel and air to a stack of fuel cells located within a hot box, operating the stack to generate an anode exhaust and a cathode exhaust, and in a low current draw steady state mode in which insufficient current is drawn from the stack to maintain a predetermined steady state stack operating temperature, supplying a first amount of the anode exhaust and the cathode exhaust to an anode tail gas oxidizer (ATO) located within the hot box to oxidize the anode exhaust and generate heat that is supplied to the stack, and in a normal steady state mode in which sufficient current is drawn from the stack to maintain the predetermined steady state stack operating temperature, either ceasing to supply the anode exhaust to the anode tail gas oxidizer or supplying a second amount of the anode exhaust to the anode tail gas oxidizer that is less than the first amount, while supplying the anode exhaust and the cathode exhaust outside the hot box.

[0006] The accompanying drawings, which are incorporated in and constitute a part of this specification, and together with the general description above and the detailed description below, illustrate exemplary embodiments of the invention. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of a solid oxide fuel cell (SOFC) system according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of a SOFC system according to a second embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram of a SOFC system according to a third embodiment of the present disclosure. [Figure 4] FIG. 4 is a cross-sectional view of a portion of a central column 101 that may be included in the SOFC systems of FIGS. [Figure 5] FIG. 5 is a schematic diagram of a combined heat and power (CHP) system connected to a fuel cell system according to various embodiments of the present disclosure. [Figure 6] FIG. 6 is a flow diagram illustrating a method of using a SOFC system according to various embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] Various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References to specific examples and implementations are made for illustrative purposes and are not intended to limit the scope of the invention or the claims.

[0009] In solid oxide fuel cell (SOFC) systems, the fuel inlet stream can be humidified to promote fuel reforming reactions, such as steam reforming and the water-gas shift reaction. Additionally, water can be added to the fuel inlet stream to prevent coking of system components, such as catalysts, during system startup, shutdown, and power grid interruption events. Traditionally, such humidification is accomplished by evaporating water in a steam generator containing corrugated tubing. The water flows through the corrugated tubing and is heated by the cathode recuperator exhaust stream, which flows around the outside of the tubing. However, utilizing the relatively low temperature of the cathode recuperator exhaust stream typically requires a significant length of corrugated tubing to absorb enough heat to vaporize the water. Furthermore, steam generators are relatively large and bulky, thereby increasing the size, complexity, and manufacturing costs of the system.

[0010] In contrast, embodiments of the present disclosure provide a water injector configured to inject water directly into the anode exhaust recirculation stream, thereby providing heat to evaporate the water into water vapor and / or aerosolize the water into droplets small enough to be entrained in the anode exhaust stream. The anode exhaust recirculation stream is recirculated into the fuel inlet stream that is fed into the fuel cell stack, providing humidified fuel to the fuel cells in the fuel cell stack. Thus, prior art steam generators can be eliminated to reduce system size, complexity, and cost. Additionally, embodiment systems can operate using relatively short, non-corrugated water conduits, thereby improving system response time and reducing system size and cost.

[0011] FIG. 1 is a schematic diagram of a SOFC system 10 according to a first embodiment of the present disclosure. Referring to FIG. 1, the system 10 includes a hot box 100 and various components disposed within or adjacent thereto. The hot box 100 can include at least one stack 102 of fuel cells, such as a solid oxide fuel cell stack including alternating fuel cells and interconnects. Each solid oxide fuel cell in the stack includes 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 nickel-YSZ, nickel-SSZ, or nickel-doped ceria cermet; and a cathode electrode, such as lanthanum strontium manganite (LSM). The interconnect can be a metal alloy interconnect, such as a chromium-iron alloy interconnect. The stacks 102 can be arranged one on top of the other in multiple columns.

[0012] Hot box 100 may also include an anode recuperator heat exchanger 110, a cathode recuperator heat exchanger 120, an anode tail gas oxidizer (ATO) 130, an anode exhaust cooling heat exchanger 140, an optional splitter 170, and a water injector 160. System 10 may also include a catalytic partial oxidation (CPOx) reactor 200, a mixer 210, a CPOx blower 204 (e.g., an air blower), a system blower 208 (e.g., an air blower), and an anode recirculation blower 212, which may be located outside hot box 100. However, the present disclosure does not limit each of the components to a particular location with respect to hot box 100.

[0013] The CPOx reactor 200 receives a fuel inlet flow from fuel inlet 300 through fuel conduit 300A. Fuel inlet 300 may be a fuel tank or a utility natural gas line with a valve controlling the amount of fuel supplied to the CPOx reactor 200. A CPOx blower 204 may supply air to the CPOx reactor 200 during system startup. Fuel and / or air may be supplied to the mixer 210 by fuel conduit 300B. Fuel flows from the mixer 210 through fuel conduit 300C to the anode recuperator 110. The fuel is heated in the anode recuperator 110 by the fuel exhaust, and then the fuel flows from the anode recuperator 110 through fuel conduit 300D to the stack 102.

[0014] The system blower 208 can be configured to supply an air flow (e.g., an air inlet flow) to the anode exhaust cooler 140 through air conduit 302A. The air flows from the anode exhaust cooler 140 through air conduit 302B to the cathode recuperator 120. The air is heated by the ATO exhaust in the cathode recuperator 120. The air flows from the cathode recuperator 120 to the stack 102 through air conduit 302C.

[0015] Anode exhaust (e.g., a fuel exhaust stream) generated within the stack 102 is supplied to the anode recuperator 110 through an anode exhaust conduit 308. The anode exhaust may include unreacted fuel and may also be referred to herein as fuel exhaust. The anode exhaust may be supplied from the anode recuperator 110 to the mixer 210 by a recirculation conduit 310, which may include a first recirculation conduit 310A and a second recirculation conduit 310B. In particular, the first recirculation conduit 310A may fluidly connect an outlet of the anode recuperator 110 to an inlet of the anode exhaust cooler 140. The second recirculation conduit 310B may fluidly connect an outlet of the anode exhaust cooler 140 to an inlet of the mixer 210.

[0016] Water flows from a water source 206, such as a water tank or water pipe, through a water conduit 306 to the water injector 160. The water injector 160 can be configured to inject water into the anode exhaust flowing through a first recirculation conduit 310A. Heat from the anode exhaust (also referred to as the recirculated anode exhaust stream) evaporates the water to generate water vapor, thereby humidifying the anode exhaust. The humidified anode exhaust is supplied to the anode exhaust cooler 140. Heat from the anode exhaust supplied to the anode exhaust cooler 140 can be transferred from the system blower 208 to the air inlet stream supplied to the cathode recuperator 120. The cooled, humidified anode exhaust can then be supplied from the anode exhaust cooler 140 to the mixer 210 via a second recirculation conduit 310B. An anode recirculation blower 212 can be configured to move the anode exhaust through the second recirculation conduit 310B.

[0017] The mixer 210 is configured to mix the humidified anode exhaust with fresh fuel (i.e., the fuel inlet stream). This humidified fuel mixture may then be heated in the anode recuperator 110 by the anode exhaust before being delivered to the stack 102. The system 10 may also include one or more fuel reforming catalysts 112, 114, and 116 located within and / or downstream of the anode recuperator 110. The reforming catalyst(s) reform the humidified fuel mixture before it is delivered to the stack 102.

[0018] The splitter 170 can be operatively connected to the first recirculation conduit 310A and can be configured to divert a portion of the anode exhaust to the ATO 130 via the ATO conduit 312A. The ATO conduit 312A can be fluidly connected to the cathode exhaust conduit 304A or the ATO 130.

[0019] Cathode exhaust generated in the stack 102 is supplied to the ATO 130 by cathode exhaust conduit 304A. The cathode exhaust can be mixed with the anode exhaust before or after being supplied to the ATO 130. The mixture of anode exhaust and cathode exhaust can be oxidized in the ATO 130 to generate ATO exhaust. The ATO exhaust flows from the ATO 130 through cathode exhaust conduit 304B to the cathode recuperator 120. The exhaust flows from the cathode recuperator 120 out of the hot box 100 through cathode exhaust conduit 304C.

[0020] The system 10 may further include a system controller 225 configured to control various elements of the system 10. The controller 225 may include a central processing unit configured to execute stored instructions. For example, the controller 225 may be configured to control fuel and / or air flow through the system 10 according to fuel composition data.

[0021] The inventors have determined that during steady-state operation when a sufficient electrical load is applied to the fuel cell stack, the heat generation of the ATO may not be required to maintain the desired steady-state operating temperature of the SOFC stack 102 (e.g., above 700°C, e.g., 750°C-900°C). However, in conventional systems, during steady-state mode, the ATO may still operate to oxidize carbon monoxide present in the anode exhaust that is supplied to the ATO. However, this oxidation may result in the release of a significant amount of heat that may not be required for steady-state operation.

[0022] Conventionally, the flow rate of the system airflow (i.e., the air inlet flow) supplied by the system blower 208 can be increased to compensate for such ATO heat dissipation. However, as the airflow rate increases, the temperature range of the fuel cells in the stack may also increase. For example, a higher airflow rate may result in certain fuel cells operating at a less-than-optimal temperature, thereby reducing total power production. In addition, a higher airflow rate may also result in more pressure drop along the airflow path. Both a higher airflow rate and a higher pressure drop may result in a higher total balance-of-plant power consumption for the system and a lower overall system efficiency.

[0023] In view of these and / or other problems of conventional systems, in some embodiments of the present disclosure, at least during steady-state operation of the system, the anode exhaust can be mixed with the cathode exhaust exiting the hot box 100 or with an alternative fresh air stream, instead of being fed to the ATO. In some embodiments, a catalyst is utilized to assist in the oxidation of carbon monoxide, hydrocarbon fuel, and / or hydrogen remaining in the anode exhaust. In alternative embodiment systems using only hydrogen fuel, the anode exhaust can be vented directly from the hot box 100, if desired. In combined heat and power (CHP) configurations, the anode exhaust can be vented into the cathode exhaust conduit upstream of the CHP heat exchanger, providing heat that is recovered in the CHP heat exchanger.

[0024] 1 , the SOFC system 10 may include a bypass conduit 316, a bypass valve 320, and an exhaust oxidizer 330. The bypass conduit 316 fluidly connects the second recirculation conduit 310B to the cathode exhaust conduit 304C. In some embodiments, the bypass conduit 316 may be connected to the second recirculation conduit 310B downstream of the anode recirculation blower 212 with respect to the anode exhaust flow direction through the second recirculation conduit 310B to provide additional exhaust flow pressure to the cathode exhaust conduit 304C. However, in other embodiments, the bypass conduit 316 may be fluidly connected to the second recirculation conduit 310B upstream of the anode recirculation blower 212.

[0025] The exhaust oxidizer 330 may be configured to oxidize the ATO exhaust output from the ATO 130 and / or the anode exhaust output from the bypass conduit 316. For example, the exhaust oxidizer 330 may include tubes or conduits containing a catalyst that promotes the oxidation of carbon monoxide and / or hydrogen to carbon dioxide and / or water, respectively. In one embodiment, the exhaust oxidizer 330 is located outside the hot box 100. Thus, heat generated by the exhaust oxidizer 330 is not used to heat the SOFC stack 102.

[0026] The ATO conduit 312A supplies the anode exhaust (e.g., ATO fuel stream) output from the splitter 170 to the ATO 130. The anode exhaust flow from the splitter 170 through the ATO conduit 312A can be controlled by controlling the speed of the anode recirculation blower 212. For example, a faster anode recirculation blower 212 can result in less anode exhaust flow to the ATO 130, and a slower anode recirculation blower 212 can result in more anode exhaust flow to the ATO 130. In some embodiments, the speed of the anode recirculation blower 212 can be limited to prevent backflow of cathode exhaust through the ATO conduit 312A and into the splitter 170.

[0027] The bypass valve 320 can be located outside the hot box 100 to prevent damage to the bypass valve 320 due to exposure to high temperatures inside the hot box 100. The bypass valve 320 can be configured to control the flow of anode exhaust from the anode exhaust conduit 310 through the bypass conduit 316. In particular, during start-up of the system 10, the bypass valve 320 can be closed to prevent the anode exhaust from being provided to the exhaust oxidizer 330 and the cathode exhaust conduit 304C, and the anode recirculation blower 212 can be operated at a speed that does not draw all of the anode exhaust from the hot box 100 so that the ATO fuel flow can be provided to the ATO 130. Thus, the ATO 130 operates to oxidize the anode exhaust using the cathode exhaust to generate heat during the start-up mode of the system 10. The heat of the ATO is used to raise the temperature of the stack 102 during start-up mode before the stack 102 reaches its steady-state operating temperature (eg, above 700°C, e.g., 750°C to 900°C).

[0028] In contrast, during steady-state operation after the stack 102 has reached its steady-state operating temperature (e.g., a temperature above 700°C, e.g., 750°C to 900°C), the bypass valve 320 can be opened so that at least a portion of the anode exhaust is supplied to the cathode exhaust conduit 304C and the exhaust oxidizer 330 via the bypass conduit 316, and the speed / flow rate of the anode recirculation blower 212 can be increased to minimize the amount of anode exhaust supplied to the ATO 130 via conduit 312A while preventing backflow of the cathode exhaust.

[0029] Thus, if sufficient current is drawn from the stack 102 (i.e., if the stack outputs power above a threshold specific to the stack 102), the stack 102 generates enough heat to maintain a desired steady-state operating temperature during steady-state mode, and the stack 102 does not require the heat of the ATO. In some embodiments, the anode exhaust is supplied to the ATO 130 during start-up mode and / or during a low current draw steady-state mode when insufficient current is drawn from the stack 102 to maintain a desired steady-state operating temperature.

[0030] For example, when the system controller 225 detects that the current drawn from the stack 102 is below a predetermined current threshold necessary to maintain a desired steady-state operating temperature (i.e., a stack operating temperature value above the temperature threshold (e.g., a temperature above 700°C, e.g., 750°C to 900°C)), a portion of the anode exhaust is supplied to the ATO 130 to generate heat within the ATO 130. The ATO heat is supplied to the stack 102 to maintain the stack above the temperature threshold. The current threshold depends on the size of the stack, the configuration of the fuel cells, the composition of the fuel supplied to the stack, the cumulative level of stack degradation, etc. In one embodiment, the current threshold may include 10 amps to 30 amps, e.g., 20 amps to 25 amps. The anode exhaust may or may not be supplied to the exhaust oxidizer 330 during the low current draw steady-state mode.

[0031] When the system controller 225 detects that sufficient current is being drawn in the stack 102 that equals or exceeds the current threshold required to maintain the stack above the temperature threshold, the system 10 exits the low current draw steady state mode and enters normal steady state mode. In normal steady state mode, the flow rate of anode exhaust through the anode recirculation blower 212 is increased, and a minimal amount of the anode exhaust is provided to the ATO 130. For example, during normal steady state mode, the anode recirculation blower 212 may operate at a relatively high speed, such that a majority of the anode exhaust is drawn from the hot box 100 and provided to the exhaust oxidizer 330, with none or only a small amount (e.g., less than 20 weight percent, e.g., 1 weight percent to 10 weight percent) of the anode exhaust being provided to the ATO 130.

[0032] In one embodiment, the bypass valve 320 can be a proportional valve configured to control the anode exhaust flow rate through the bypass conduit 316. In some embodiments, the system controller 225 can be configured to gradually open the bypass valve 320 and gradually increase the speed of the anode recirculation blower 212 during the transition from startup to steady-state operation and / or during steady-state operation. Additionally, the system controller 225 can be configured to gradually reduce the speed of the system blower 208 to compensate for the reduction in heat output of the ATO 130.

[0033] The exhaust oxidizer 330 can be located outside the hot box 100 so that the heat generated by the oxidation reaction does not unnecessarily heat the system components. As a result, the overall system airflow can be reduced. In particular, the system air blower 208 can be operated at a slower speed during steady-state operation compared to when the anode exhaust is supplied to the ATO 130. In other words, the steady-state power consumption of the system blower 208 can be significantly reduced. In addition, cell-to-cell temperature fluctuations can be reduced, thereby increasing cell voltage and efficiency.

[0034] In some embodiments, system 10 may optionally include a cabinet air blower 209 configured to supply cabinet air to cathode exhaust conduit 304C or system exhaust conduit 332. In particular, system 10 may be located within a cabinet, and cabinet air blower 209 may be configured to supply cabinet air to cool the exhaust air output from system 10 in embodiments where a chiller system exhaust is required.

[0035] In various other embodiments, the system 10 may include a system exhaust conduit 332 configured to supply the exhaust gas output from the exhaust gas oxidizer 330 to a combined heat and power (CHP) system 400, as described below with respect to Figure 5. In one embodiment shown in Figure 1, additional air may be supplied to the cathode exhaust conduit 304C by the cabinet air blower 209 to reduce the exhaust gas temperature.

[0036] In some embodiments, during start-up and steady-state operating modes, a portion of the anode exhaust may be supplied to the ATO 130. In other embodiments, shown in Figures 2 and 3, the splitter 170 and ATO conduit 312A may be omitted. In these embodiments, the anode exhaust is not supplied directly from within the hot box 100 to the ATO 130 during any operating mode.

[0037] Figure 2 is a schematic diagram of a SOFC system 12 according to a second embodiment of the present disclosure. The SOFC system 12 is similar to the SOFC system 10 of Figure 1. Therefore, only the differences from the SOFC system 10 will be described in detail.

[0038] 2 , the SOFC system 12 may include a bypass conduit 316A, an ATO conduit 312B, and an ATO valve 324. The bypass conduit 316A may fluidly connect the second recirculation conduit 310B to the cathode exhaust conduit 304C upstream of the anode recirculation blower 212. However, in other embodiments, if more anode exhaust flow is required, the bypass conduit 316A may be connected to the second recirculation conduit 310B downstream of the anode recirculation blower 212. The ATO conduit 312B may fluidly connect the bypass conduit 316A to the ATO 130.

[0039] Bypass valve 320 can be configured to control the flow of anode exhaust through bypass conduit 316A, and ATO valve 324 can be configured to control the flow of anode exhaust (e.g., ATO fuel flow) through ATO conduit 312B to ATO 130. In some embodiments, valves 320 and 324 can be proportional valves configured to provide different flow rates through the respective conduits 316A and 312B. In particular, during system startup, system controller 225 can close bypass valve 320 and open ATO valve 324, thereby providing anode exhaust to ATO 130 but not to cathode exhaust conduit 304C and exhaust oxidizer 330.

[0040] During steady-state operation, the system controller 225 can open the bypass valve 320 and close the ATO valve 324, thereby diverting a portion of the anode exhaust in the second recirculation conduit 310B into the cathode exhaust conduit 304C and supplying it to the exhaust oxidizer 330, but preventing the anode exhaust from being supplied to the ATO 130 via the ATO conduit 312B.

[0041] In some embodiments, the system controller 225 can be configured to gradually open the bypass valve 320 and gradually close the ATO valve 324 during the transition from startup to steady-state operation and / or during steady-state operation. Additionally, the system controller 225 can be configured to gradually reduce the speed of the system blower 208 to compensate for the reduced thermal output of the ATO 130 as the ATO fuel flow decreases and / or after the ATO fuel flow is stopped.

[0042] Figure 3 is a schematic diagram of a SOFC system 14 according to a third embodiment of the present disclosure. The SOFC system 14 is similar to the SOFC system 12 of Figure 2. Therefore, only the differences from the SOFC system 12 will be described in detail.

[0043] 3 , the SOFC system 14 may include a bypass conduit 316B fluidly connecting the first recirculation conduit 310A to the cathode exhaust conduit 304C. In other words, the bypass conduit 316B may be configured to divert anode exhaust flowing from the anode recuperator 110 to the anode exhaust cooler 140 to the cathode exhaust conduit 304C, thereby diverting a portion of the anode exhaust to the exhaust oxidizer 330 upstream of the anode exhaust cooler 140. The optional ATO conduit 312B fluidly connects the bypass conduit 316B to the ATO 130.

[0044] Bypass valve 320 can be configured to control the flow of anode exhaust through bypass conduit 316B, and ATO valve 324 can be configured to control the flow of anode exhaust through ATO conduit 312B to ATO 130. In particular, during system startup, system controller 225 can close bypass valve 320 and open ATO valve 324, thereby providing anode exhaust to ATO 130 but not to cathode exhaust conduit 304C and exhaust oxidizer 330. During steady-state operation, system controller 225 can open bypass valve 320 and close ATO valve 324, thereby providing anode exhaust to exhaust oxidizer 330 and not to ATO 130.

[0045] In some embodiments, the system controller 225 can be configured to gradually open the bypass valve 320 and gradually close the ATO valve 324 during the transition from startup to steady-state operation and / or during steady-state operation. Additionally, the system controller 225 can be configured to gradually reduce the speed of the system blower 208 to compensate for the reduced thermal output of the ATO 130 as the ATO fuel flow decreases and / or after the ATO fuel flow is stopped.

[0046] FIG. 4 is a cross-sectional view of a portion of a central column 101 that may be included in the SOFC systems 10, 12, and / or 14. Referring to FIGS. 1-4, the central column 101 may include an anode recuperator 110, an ATO 130, and an anode exhaust cooler 140. The anode recuperator 110 is located within the core of the central column 101. The ATO 130 may include a toroidal manifold containing an ATO catalyst that surrounds the anode recuperator 110. The anode exhaust cooler 140 may be located above the anode recuperator 110 and the ATO 130. A stack of fuel cells 102 may surround the ATO 130, and a cathode recuperator 120 may surround the stack of fuel cells 102.

[0047] The ATO conduit 312, which may be any of the ATO conduits 312A, 312B, and 312C described above, may be divided into two or more column conduits (e.g., two to six manifold tubes) 314 extending from the top of the central column 101 to the ATO injector 172. The ATO injector 172 may comprise an annular space having a radially inner wall 174 connected to the outlet of the column conduit 314 and an outer wall 176 projecting into the top of the ATO 130. In one embodiment, the outer wall 176 may have a curved vertical profile with a central section projecting radially outward from tapered top and bottom sections. The outer wall 176 includes one or more openings 178, such as slits, located in the central section. The openings 178 fluidly connect the interior space of the ATO injector 172 to the interior space of the ATO 130. In particular, the column conduit 314 can be configured to deliver multiple anode exhaust streams from the ATO conduit 312 to the ATO 130 through openings 178 in the ATO injector 172, as shown by the dashed arrows in Figure 4. Radial separation of the anode exhaust stream into multiple anode exhaust streams in the ATO injector improves the radial flow and mixing of the anode exhaust within the ATO 130.

[0048] 1-3 for the first through third embodiments, the exhaust oxidizer 330 may be omitted from the SOFC systems 10, 12, 14 if the system operates using hydrogen as the fuel source. In one embodiment shown in FIG. 1, if the exhaust oxidizer 330 is omitted, additional air may be supplied to the cathode exhaust conduit 304C by the cabinet air blower 209 to reduce the exhaust temperature.

[0049] In various embodiments, the exhaust oxidizer 330 can include an oxidation catalyst such as that described in U.S. Provisional Patent Application No. 63 / 220,659, filed July 12, 2021, which is incorporated herein by reference in its entirety. For example, the oxidation catalyst can include a D-block metal, such as gold (Au), and / or one or more platinum group metals, such as platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os), ruthenium (Ru), or a combination thereof. In some embodiments, Au, Pt, Pd, and Rh can exhibit the highest catalytic activity. In some embodiments, the oxidation catalyst can include Au and / or a platinum group metal stabilized with another metal, such as manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and / or copper (Cu).

[0050] In various embodiments, the anode exhaust may be diverted from the anode exhaust stream flowing from the anode recuperator 110 to the anode exhaust cooler 140 or from the anode exhaust stream output from the anode exhaust cooler 140 and supplied to an exhaust oxidizer 330 located outside the hot box 100. The anode exhaust flow to the ATO 130 may be reduced and / or shut off during steady-state operation to reduce heat generation in the ATO 130, and system airflow may be correspondingly reduced, thereby increasing temperature uniformity and performance throughout the system.

[0051] In some embodiments, the SOFC systems 10, 12, 14 may operate under low current load conditions or in response to transients in current load conditions (e.g., in steady-state mode), which may require additional heat to maintain stack operating temperatures. In such conditions, anode exhaust may be periodically supplied to the ATO 130 to periodically increase the temperature within the hot box 100. For example, the anode exhaust may be supplied to the ATO on a schedule based on the amount of additional heating required to maintain stack operating temperatures, such as 5 to 20 seconds per minute, 30 seconds to 3 minutes every 10 minutes, 5 to 15 minutes per hour, etc. In these embodiments, valve 320 may be periodically closed and / or valve 324 (if present) may be periodically opened to supply a portion of the anode exhaust to the ATO 130 during steady-state mode. After the anode exhaust is supplied to the ATO via conduit 312A or 312B, valve 320 may be opened and / or valve 324 (if present) may be closed. These steps of opening and closing valve(s) 320 and / or 324 may be repeated periodically. Alternatively or additionally, the speed / flow rate of the anode recirculation blower 212 may be varied periodically to control the amount of anode exhaust delivered to the ATO 130. For example, the speed may be decreased for a first period of time to supply or increase the amount of anode exhaust delivered to the ATO 130. The speed may then be increased for a second period of time to stop or reduce the amount of anode exhaust flowing to the ATO 130. The above steps may be repeated periodically in response to low output current or transient currents, which may be detected by measuring the current output by the stack and / or by measuring the temperature of the stack using a thermocouple or another suitable temperature sensor.

[0052] 5 is a schematic diagram of a CHP system 400 according to various embodiments of the present disclosure. Referring to FIG. 5, the CHP system 400 may include a heat exchanger 410, a boiler 420, a steam turbine 422, and a generator 424. The boiler 420 provides steam to operate the turbine 422, which rotates the generator 424 to generate electricity.

[0053] The heat exchanger 410 may be configured to receive water from the water inlet conduit 412 and the hot exhaust stream output from the exhaust oxidizer 330 via conduit 332 of the SOFC system 10, 12, or 14, as described above. In particular, the heat exchanger 410 may be configured to extract heat from the exhaust stream to heat the water provided from the water inlet conduit 412 and produce steam and / or hot water. The heated water (or a mixture of heated water and steam) may be supplied to the boiler 420. Alternatively, a fully evaporated (and possibly superheated) steam stream may be supplied to the turbine 422. The hot exhaust stream is cooled within the heat exchanger 410 and exhausted from the heat exchanger 410 through outlet conduit 414. Thus, the heat exchanger 410 may reduce the fuel consumption of the boiler 420 for a given amount of power output from the generator 424 by utilizing the heat output from the SOFC system.

[0054] Additional water and fuel may be supplied to the boiler 420, which boils water and supplies steam to a steam turbine 422. The steam and / or hot water may be supplied from the steam turbine 422 to a cooling or heating system 430 of a structure 432 (e.g., a building or facility such as a factory). Electricity generated by a generator 424 is supplied to the structure 432 and / or a power grid 434. In some embodiments, a steam superheater 421 may be fluidly connected between the boiler 420 and the steam turbine 422. The steam superheater 421 may be configured to superheat steam output from the boiler 420 by extracting heat from flue gas generated by the combustion of the boiler fuel.

[0055] 6 is a flowchart illustrating steps of a method of operating a fuel cell system according to various embodiments of the present disclosure. The method is described with respect to a generic SOFC system, which may include components as described with respect to any of the fuel cell systems 10, 12, 14 disclosed herein.

[0056] 1-6, in step 502, the SOFC system operates in start-up mode. In particular, fuel may be supplied to the stack 102 through the fuel inlet 300, and air may be supplied to the stack by the system air blower 208. In addition, anode exhaust and cathode exhaust generated by the stack 102 may be supplied to the ATO 130 for oxidation, which may provide heat and increase the temperature of the stack 102.

[0057] For example, the speed of the anode recycle blower 212 can be reduced and / or the ATO valve 324 can be opened to provide anode exhaust to the ATO 130 via the respective ATO conduit 312A or 312B. Additionally, the bypass valve 320 can be closed to prevent anode exhaust from flowing through the bypass conduit 316. In some embodiments, the CPOx reactor 200 can be operated to partially reform the fuel during start-up mode.

[0058] Once the stack 102 reaches the set steady-state operating temperature, the SOFC system may transition to steady-state mode. In particular, in step 504, the anode exhaust flow to the ATO 130 may be stopped or reduced. For example, the speed of the anode recirculation blower 212 may be increased and / or the ATO valve 324 may be closed to stop the anode exhaust flow to the ATO 130 through the respective ATO conduit 312A or 312B.

[0059] In step 506, a portion of the anode exhaust generated by stack 102 can be diverted to exhaust oxidizer 330, where a mixture of anode exhaust and cathode exhaust can react to oxidize carbon monoxide and / or hydrogen. For example, bypass valve 320 can be opened to divert a portion of the anode exhaust to exhaust oxidizer 330. For example, the anode exhaust can be diverted from either conduit 310A or 310B upstream or downstream of anode exhaust cooler 140.

[0060] The anode exhaust can be diverted by closing the ATO valve 324, and a portion of the anode exhaust generated by the stack 102 can be diverted to the exhaust oxidizer 330 for oxidizing the cathode exhaust. For example, the bypass valve 320 can be opened so that a portion of the anode exhaust is diverted from conduit 310A or 310B to the exhaust oxidizer 330 via bypass conduit 316, 316A, or 316B. In various embodiments, the flow rate of anode exhaust to the exhaust oxidizer 330 during steady-state operation can be less than the anode exhaust flow rate to the ATO 130 during start-up operation.

[0061] In step 508, the system air flow rate may optionally be adjusted based on changes in the temperature of the SOFC system. For example, the speed of the system air blower 208 may be adjusted based on the temperature of the stack 102. In particular, if the temperature of the stack 102 decreases due to a reduction in the thermal output of the ATO 130, the air flow rate of the system air blower 208 may be correspondingly reduced.

[0062] In some embodiments, in step 510, the method may optionally include supplying the exhaust air output from the exhaust air oxidizer 330 to a combined heat and power (CHP) system 400. For example, the exhaust air may be supplied to a heat exchanger 410 to provide steam and / or hot water.

[0063] In some embodiments, the method can operate the SOFC system in a low-current-draw steady-state mode. For example, if the current load applied to the stack is insufficient to maintain a predetermined steady-state stack operating temperature, step 504 can include periodically supplying the anode exhaust to the ATO 130 to generate heat that is supplied to the stack 102 so that the temperature of the stack 102 can be maintained within a selected operating temperature range. For example, the anode exhaust can be periodically supplied to the ATO 130, where it is mixed with the cathode exhaust and continuously supplied to the ATO 130. For example, the anode exhaust can be supplied according to a schedule that can be based on the amount of heating required to maintain the stack 102 at a particular operating temperature or temperature range. For example, the anode exhaust can be supplied over X minutes for a period of Y, where X can be in a range from about 10 seconds to about 5 minutes, e.g., from about 30 seconds to about 3 minutes, and Y can be in a range from about 5 minutes to about 1 hour, e.g., from about 10 minutes to about 30 minutes.

[0064] Thus, in a start-up mode and / or a low current draw steady state mode in which insufficient current is drawn from the stack to maintain a predetermined steady state stack operating temperature, a first amount (e.g., a first volume or flow rate) of anode exhaust and cathode exhaust is supplied to the ATO 130 located within the hot box 100 to oxidize the anode exhaust and generate heat that is supplied to the stack 102. In contrast, in a normal steady state mode in which sufficient current is drawn from the stack to maintain a predetermined steady state stack operating temperature, the anode exhaust flow to the ATO is stopped, or a second amount (e.g., a second volume or flow rate) of anode exhaust that is less than the first amount is supplied to the ATO 130, while another portion (i.e., amount) of the anode exhaust and cathode exhaust is supplied to the exhaust oxidizer 330 located outside the hot box 100.

[0065] The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art. Furthermore, the general principles defined herein may be applied to other embodiments without departing from the scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. 1. A fuel cell system, comprising: a stack of fuel cells configured to output an anode exhaust and a cathode exhaust; an anode tail gas oxidizer configured to oxidize the anode exhaust from the stack of fuel cells; a cathode exhaust conduit configured to output the cathode exhaust and the anode exhaust from the fuel cell system; a bypass conduit configured to divert the anode exhaust from the stack of fuel cells to the cathode exhaust conduit; a bypass valve configured to control the flow of the anode exhaust through the bypass conduit; an ATO conduit configured to deliver the anode exhaust from the fuel cell stack to the anode tail gas oxidizer; an anode recuperator configured to use the anode exhaust from the fuel cell stack to heat fuel supplied to the fuel cell stack; an anode exhaust conduit configured to supply anode exhaust output from the fuel cell stack to the anode recuperator; an anode exhaust cooler configured to use the anode exhaust from the anode recuperator to heat air supplied to the fuel cell stack; Equipped with The fuel cell system, wherein the bypass conduit is configured to divert the anode exhaust from the stack of fuel cells after it has passed through the anode recuperator or after it has passed through both the anode recuperator and the anode exhaust cooler.

2. a hot box containing the stack, the anode tail gas oxidizer, the anode recuperator, and the anode exhaust cooler; an exhaust oxidizer configured to oxidize the anode exhaust received from the cathode exhaust conduit; Further provided with The fuel cell system of claim 1 , wherein the exhaust oxidizer is located outside the hot box.

3. an ATO injector comprising an annular space having a radially inner wall and an outer wall extending into the anode tail gas oxidizer, the ATO injector including one or more openings fluidly connecting the interior space of the ATO injector to the interior space of the anode tail gas oxidizer; at least one column conduit fluidly connecting the ATO conduit to the interior space of the ATO injector and extending through a central column of the fuel cell system to the ATO injector; a mixer configured to mix the anode exhaust with fresh fuel; a first recirculation conduit fluidly connecting an outlet of the anode recuperator to an inlet of the anode exhaust cooler; a second recirculation conduit fluidly connecting an outlet of the anode exhaust cooler to the mixer; an anode recirculation blower operatively connected to the second recirculation conduit; The fuel cell system of claim 1 further comprising:

4. the bypass conduit is fluidly connected to the second recirculation conduit upstream of the anode recirculation blower with respect to a flow direction of the anode exhaust through the second recirculation conduit; The fuel cell system of claim 3 , wherein the ATO conduit is fluidly connected to the bypass conduit.

5. the bypass conduit is fluidly connected to the second recirculation conduit downstream of the anode recirculation blower with respect to a flow direction of the anode exhaust through the second recirculation conduit; a splitter configured to split a portion of the anode exhaust flowing through the first recirculation conduit; The fuel cell system of claim 4 , wherein the ATO conduit fluidly connects the splitter to the ATO injector.

6. the bypass conduit is fluidly connected to the first recirculation conduit; The fuel cell system of claim 3 , wherein the ATO conduit fluidly connects the bypass conduit to the ATO injector.

7. a system air blower configured to supply air to the stack through the anode exhaust cooler; an ATO valve located outside the hot box and configured to control the flow of the anode exhaust through the ATO conduit; a system controller configured to control the bypass valve, the ATO valve, and the system air blower; Further provided with The system controller During a start-up mode of the fuel cell system, the ATO valve is opened and the bypass valve is closed; configured to close the ATO valve and open the bypass valve during a steady state mode of the fuel cell system after the fuel cell stack has reached a steady state operating temperature; 10. The fuel cell system of claim 1, wherein the system controller is configured to gradually reduce the operating speed of the system air blower during the steady state mode to maintain the fuel cell stack at the steady state operating temperature.

8. a system exhaust conduit fluidly connecting an outlet of the exhaust oxidizer to a combined heat and power system; The cogeneration system comprises: a heat exchanger configured to use heat extracted from the exhaust air provided by the system exhaust conduit to produce hot water or steam; Boiler and The turbine and A generator and The fuel cell system of claim 2 , comprising:

9. The fuel cell system of claim 1 , wherein the stack comprises a solid oxide fuel cell stack.

10. In a start-up mode, the fuel cell system is configured to supply a first amount of the anode exhaust and the cathode exhaust to the anode tail gas oxidizer located within a hot box to oxidize the anode exhaust and generate heat that is supplied to the stack; In a steady-state mode, the fuel cell system is configured to stop supplying the anode exhaust to the anode tail gas oxidizer, or to supply the anode exhaust to the anode tail gas oxidizer at a second amount less than the first amount, and to supply the anode exhaust and the cathode exhaust outside the hot box. The fuel cell system according to claim 1 .

11. in a low current draw steady state mode in which insufficient current is drawn from the stack to maintain a predetermined steady state stack operating temperature, the fuel cell system is configured to supply a first amount of the anode exhaust and the cathode exhaust to the anode tail gas oxidizer located within a hot box to oxidize the anode exhaust and generate heat that is supplied to the stack; and in a normal steady-state mode in which sufficient current is drawn from the stack to maintain the predetermined steady-state stack operating temperature, the fuel cell system is configured to either stop supplying the anode exhaust to the anode tail gas oxidizer or supply a second amount of the anode exhaust to the anode tail gas oxidizer, the second amount being less than the first amount, and supply the anode exhaust and the cathode exhaust outside the hot box. The fuel cell system according to claim 1 .

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