Fuel cell system with air inlet baffle and method of operation thereof

Abstract

To provide an air inlet baffle intended to heat air using cathode exhaust output from a stack.SOLUTION: A fuel cell system includes a stack 102 of fuel cells, a cathode recuperator 500 configured to heat air using cathode exhaust output from the stack 102, and an air inlet baffle 550 which is disposed between the cathode recuperator 500 and the stack 102, has at least two rows of apertures separated along a vertical direction, and is configured to provide the heated air output from the cathode recuperator to multiple areas of the stack.SELECTED DRAWING: Figure 2A2B

Description

Technical Field

[0001] Aspects of the present invention relate to an electrochemical cell system, and more particularly to a fuel cell system comprising an air inlet baffle having an aperture.

Background Art

[0002] A fuel cell, such as a solid oxide fuel cell, is an electrochemical device capable of efficiently converting the energy stored in a fuel into electrical energy. 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 can also operate in reverse so that, by using electrical energy as an input, oxidized fuel can be re-reduced to unoxidized fuel.

Summary of the Invention

[0003] According to various embodiments, a fuel cell system includes a stack of fuel cells, a cathode reheater configured to heat air using cathode exhaust discharged from the stack, and an air inlet baffle disposed between the cathode reheater and the stack and having at least two rows of apertures separated along a vertical direction and configured to supply heated air discharged from the cathode reheater to multiple regions of the stack.

[0004] According to various embodiments, a method for operating a fuel cell system includes supplying heated air and fuel to a stack of fuel cells; operating the stack in a steady-state mode to discharge fuel exhaust and air exhaust; supplying the fuel exhaust and air exhaust to an anode tail gas oxidizer for oxidizing the fuel exhaust; supplying the exhaust from the anode tail gas oxidizer to a cathode reheater; supplying air to the cathode reheater; heating the air using the exhaust from the anode tail gas oxidizer and discharging the heated air from the cathode reheater onto an air inlet baffle located between the cathode reheater and the stack and having at least two rows of openings separated vertically; and supplying the heated air to multiple regions of the stack through at least two rows of openings.

[0005] Exemplary embodiments of the present invention are illustrated by the accompanying drawings, which are incorporated herein and form part herein. The accompanying drawings, together with the above general description and the following detailed description, serve to illustrate the features of the present invention. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic diagram of a fuel cell system according to various embodiments of the present disclosure. [Figure 2A2B] Figure 2A is a cross-sectional view showing the components of the hotbox of the system of Figure 1 according to various embodiments of the present disclosure, and Figure 2B is a diagram showing an enlarged portion of the system of Figure 2A according to various embodiments of the present disclosure. [Figure 2C] Figure 2C is a three-dimensional cutaway view of the central column of the system shown in Figure 2A, according to various embodiments of the present disclosure. [Figure 2D] Figure 2D is a perspective view of an anode hub structure located below the central column of the system in Figure 2A, according to various embodiments of the present disclosure. [Figure 3A] Figure 3A is a cross-sectional view showing the fuel and airflow through the central column of the system in Figure 2A according to various embodiments of the present disclosure. [Figure 3B]Figure 3B is a cross-sectional view showing the fuel and airflow through the central column of the system of Figure 2A according to various embodiments of the present disclosure. [Figure 3C] Figure 3C is a cross-sectional view showing the fuel and airflow through the central column of the system in Figure 2A according to various embodiments of the present disclosure. [Figure 4A] Figure 4A is a cross-sectional view showing the air inlet baffle located inside the cathode reheater. [Figure 4B] Figure 4B is a simplified partial cross-sectional view showing the air and exhaust flow through the cathode regenerator, stack, and central column. [Figure 4C] Figure 4C is a side view of the air inlet baffle shown in Figure 4A. [Figure 5] Figure 5 is a simplified cross-sectional view showing the distribution of air from the cathode regenerator 500 to the stack in a comparative fuel cell system without an air inlet baffle. [Figure 6] Figure 6 is a graph showing the predicted mean vertical temperature profile of the cell fuel distribution (CFD) of a beginning-of-life (BOL) stack operating at 51 amperes in a fuel cell system equipped with the air inlet baffle shown in Figure 4A. [Figure 7] Figure 7 is a graph showing the average vertical fuel utilization profile from CFD, corresponding to the thermal profile of the stack tested under 51 amperes of BOL operating conditions. [Figure 8] Figure 8 is a graph showing the average vertical temperature profiles of an early-life (BOL) stack operating at 51 amperes and a middle-life (MOL) stack operating at 66 amperes (e.g., when cell conditions have deteriorated) in a fuel cell system equipped with the air inlet baffle shown in Figure 4A. [Modes for carrying out the invention]

[0007] As described herein, various aspects of this disclosure are described with reference to exemplary embodiments and / or accompanying drawings illustrating exemplary embodiments of the invention. However, the invention can be embodied in many different forms and should not be construed as being limited to the exemplary embodiments shown in the drawings or described herein. It will be understood that the various embodiments disclosed may involve specific features, elements, or steps described in relation to that particular embodiment. It will also be understood that specific features, elements, or steps described in relation to one particular embodiment may be interchangeable with alternative embodiments or combined with alternative embodiments in various unexemplified combinations or permutations.

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

[0009] In this specification, ranges can be expressed as "about" one specific value and / or "about" another specific value. An example of such a range expression is "from one specific value and / or to another specific value." Similarly, it will be understood that when a value is expressed as an approximation by using "about" or "substantially" at the beginning, a specific value takes on a different appearance. In some embodiments, the value "about X" may include the value + / -1%X. It will be further understood that each endpoint of a range is important, whether in relation to the other endpoint or independently of the other endpoint.

[0010] In a solid oxide fuel cell (SOFC) system, air and fuel can be supplied to one or more fuel cell stacks to generate electricity. During operation, the stack may experience vertical temperature gradients due to cell heat generation, convective cooling due to incoming air, and / or radiative coupling between the stack and / or other system components. For example, the temperature of a fuel cell may be lower at the top and / or bottom of the stack than at the central cell of the stack, and / or the central cell may be overcooled or overheated. Excessive vertical temperature gradients can lead to reduced voltage performance, thermal stress, cell degradation, and uneven fuel delivery, which may reduce overall system performance and / or efficiency. This may further lead to fuel depletion and associated failure of some fuel cells in the stack. Accordingly, embodiments of the present disclosure provide an SOFC system including a perforated air inlet baffle that helps improve stack temperature fluctuations and optimize the vertical stack temperature profile for uniform fuel flow to individual cells in the stack.

[0011] Figure 1 is a schematic diagram of SOFC system 10 according to various embodiments of the present disclosure. Referring to Figure 1, system 10 comprises a hot box 100 and various components arranged inside or adjacent to it. The hot box 100 may include a stack 102 that alternately includes fuel cells, such as solid oxide fuel cells, and interconnects. One solid oxide fuel cell in stack 102 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 interconnects may be metal alloy interconnects such as chromium-iron alloy interconnects. The stack 102 may be manifolded internally or externally for fuel.

[0012] The hot box 100 may also include an anode reconstitution heat exchanger 110, a cathode reconstitution heat exchanger 500, an anode tail gas oxidizer (ATO) 150, an anode exhaust cooling heat exchanger 140, a splitter 158, a vortex generator 159, and a water injector 160. The 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 main air blower 208 (e.g., a system blower), and an anode recirculation blower 212, which may be located outside the hot box 100. However, this disclosure does not limit each of the components to a specific location relative to the hot box 100.

[0013] The CPOx reactor 200 receives the fuel inlet flow from the fuel inlet 300 through the fuel conduit 300A. The fuel inlet 300 can be a fuel tank or utility natural gas line equipped with a valve that controls the amount of fuel supplied to the CPOx reactor 200. A CPOx blower 204 can supply air to the CPOx reactor 200 at system startup. Fuel and / or air can be supplied to the mixer 210 by the fuel conduit 300B. The fuel (e.g., the fuel inlet flow) flows from the mixer 210 through the fuel conduit 300C to the anode reconverter 110. The fuel is heated in the anode reconverter 110 by a portion of the fuel exhaust, and then the fuel flows from the anode reconverter 110 through the fuel conduit 300D to the stack 102.

[0014] The main air blower 208 can be configured to supply an airflow (e.g., an air inlet flow) to the anode exhaust cooler 140 through the air conduit 302A. Air flows from the anode exhaust cooler 140 through the air conduit 302B to the cathode regenerator 500. The air is heated by the ATO exhaust within the cathode regenerator 500. Air flows from the cathode regenerator 500 through the air conduit 302C to the stack 102.

[0015] The anode exhaust flow (e.g., fuel exhaust flow) generated within the stack 102 is supplied to the anode reconverter 110 through the anode exhaust conduit 308A. The anode exhaust may contain unreacted fuel and may be referred to herein as fuel exhaust. The anode exhaust can be supplied from the anode reconverter 110 to the splitter 158 through the anode exhaust conduit 308B. A first portion of the anode exhaust can be supplied from the splitter 158 to the anode exhaust cooler 140 through the water injector 160 and the anode exhaust conduit 308C. A second portion of the anode exhaust is supplied from the splitter 158 to the ATO 150 through the anode exhaust conduit 308D. The first portion of the anode exhaust heats the air inlet flow in the anode exhaust cooler 140 and can then be supplied from the anode exhaust cooler 140 to the mixer 210 through the anode exhaust conduit 308E. The anode recirculation blower 212 can be configured to move the anode exhaust through the anode exhaust conduit 308E, as will be described later.

[0016] The cathode exhaust generated within the stack 102 flows through the exhaust conduit 304A to the ATO 150. A vortex generator 159 can be positioned within the exhaust conduit 304A and configured to swirl the cathode exhaust. An anode exhaust conduit 308D can be fluidly connected to the vortex generator 159, or to the cathode exhaust conduit 304A or ATO 150 downstream of the vortex generator 159. The swirled cathode exhaust can be mixed with a second portion of the anode exhaust supplied by the splitter 158 before being supplied to the ATO 150. This mixture can be oxidized within the ATO 150 to generate ATO exhaust. The ATO exhaust flows from the ATO 150 through the exhaust conduit 304B to the cathode reconverter 500. The exhaust flows out of the hot box 100 through the exhaust conduit 304C from the cathode reconverter.

[0017] Water flows from a water source 206, such as a water tank or a water supply pipe, through a water conduit 306 to a water injector 160. The water injector 160 directly injects water into a first portion of the anode exhaust supplied into an anode exhaust conduit 308C. Due to the heat from the first portion of the anode exhaust (also referred to as the recirculated anode exhaust flow) supplied into the anode exhaust conduit 308C, the water evaporates to generate water vapor. The water vapor mixes with the anode exhaust, and the resulting mixture is supplied to an anode exhaust cooler 140. Next, this mixture is supplied from the anode exhaust cooler 140 through an anode exhaust conduit 308E to a mixer 210. The mixer 210 is configured to mix the water vapor and the first portion of the anode exhaust with a fresh fuel (i.e., the fuel inlet flow). Next, this humidified fuel mixture can be heated in an anode reheater 110 by the anode exhaust before being supplied to the stack 102. The system 10 can also include one or more fuel reforming catalysts 112, 114, and 116 located inside and / or downstream of the anode reheater 110. The reforming catalyst(s) reform the humidified fuel mixture before it is supplied to the stack 102.

[0018] The system 10 can further include a system controller 225 configured to control various elements of the system 10. The controller 并25 can include a central processing unit configured to execute stored instructions. For example, the controller 225 can be configured to control the fuel and / or air flow through the system 10 according to fuel composition data. <^

[0019] FIG. 2A is a cross-sectional view showing the components of the hot box 100 of the system 10 of FIG. 1, and FIG. 2B shows an enlarged portion of FIG. 2A. FIG. 2C is a three-dimensional cutaway view of the central column 400 of the system 10 according to various embodiments of the present disclosure, and FIG. 2D is a perspective view of an anode hub structure 600 disposed within a hot box base 101 in which the column 400 can be disposed.

[0020] Referring to Figures 2A to 2D, the fuel cell stack 102 can be arranged around the central column 400 within the hot box 100. For example, the stack 102 can be arranged in a ring configuration around the central column 400 and can be positioned on the hot box base 101. The column 400 may comprise an anode reconverter 110, an ATO 150, and an anode exhaust cooler 140. In particular, the anode reconverter 110 is positioned radially inward of the ATO 150, and the anode exhaust cooler 140 is mounted above the anode reconverter 110 and ATO 150. In one embodiment, an oxidation catalyst 112 and / or a hydrogenation catalyst 114 can be located within the anode reconverter 110. A reforming catalyst 116 may also be located at the bottom of the anode reconverter 110 as a steam methane reforming (SMR) insert.

[0021] The ATO 150 comprises an outer cylinder 152 positioned around the outer wall of the anode regenerator 110. Optionally, the ATO insulation 156 can be surrounded by an inner ATO cylinder 154. Thus, the insulation 156 can be located between the anode regenerator 110 and the ATO 150. The ATO oxidation catalyst can be located in the space between the outer cylinder 152 and the ATO insulation 156. A fuel inlet path bellows 854 can be located between the anode exhaust cooler 140 and the inner ATO cylinder 154. An ATO thermocouple feedthrough 1601 extends through the anode exhaust cooler 140 to the top of the ATO 150. This allows the temperature of the ATO 150 to be monitored by inserting one or more thermocouples (not shown) through this feedthrough 1601.

[0022] The anode hub structure 600 can be positioned below the anode reheater 110 and ATO 150 and above the hot box base 101. The anode hub structure 600 is covered by the ATO skirt 1603. The vortex generator 159 and fuel exhaust splitter 158 are positioned above the anode reheater 110 and ATO 150 and below the anode exhaust cooler 140. An ATO glow plug 1602, which initiates oxidation of the stacked fuel exhaust in the ATO during startup, can be positioned near the bottom of the ATO 150.

[0023] The anode hub structure 600 is used to uniformly distribute fuel from the central column to the fuel cell stack 102, which is arranged around the central column 400. The anode flow hub structure 600 comprises a grooved cast base 602 and a "spider" hub consisting of a fuel inlet conduit 300D and an anode exhaust conduit 308A. Each pair of conduits 300D, 308A connects to the fuel cell stack 102. In addition, the anode side cylinders (e.g., the inner and outer cylinders of the anode reconverter 110, and the ATO outer cylinder 152) are welded or brazed into the grooves of the base 602 to provide a uniform volume cross-section for the flow distribution described later.

[0024] As indicated by the arrows in Figures 2A and 2B, air enters from the top of the hot box 100 and then flows into the cathode regenerator 500, where it is heated by the ATO exhaust discharged from the ATO 150. The heated air then flows through the cathode regenerator 500 and exits the cathode regenerator 500 through the air outlet 530. An air inlet baffle 550 can be placed between the stack 102 and the cathode regenerator 500. As will be described in detail later, the air inlet baffle 550 can be configured to control the airflow to the stack 102.

[0025] In the case of a solid oxide fuel cell, air then flows through the stack 102, and oxygen ions diffuse from the cathode electrode through the fuel cell electrolyte to the anode electrode, where they react with the fuel supplied from the anode hub structure 600 at the anode electrode of the fuel cell (i.e., the fuel inlet flow). The exhaust air flows out of the stack 102, then swirls through the blades of the vortex generator 159, and enters the ATO 150.

[0026] The splitter 158 can direct a second portion of the fuel exhaust exiting the top of the anode reconverter 100 through an opening (e.g., a slit) in the splitter to a swirling air exhaust (e.g., into the vortex generator 159, or into the exhaust conduit 304A downstream of the vortex generator 159, or into the ATO 150). Thus, the fuel and air exhaust can be mixed before entering the ATO 150.

[0027] Figures 3A and 3B are side cross-sectional views showing the flow distribution through the central column 400, and Figure 3C is a top cross-sectional view through the anode reconverter 110. Referring to Figures 2A, 2B, 3A, and 3C, the anode reconverter 110 comprises an inner cylinder 110A, a corrugated plate 110B, and an outer cylinder 110C which can be covered by ATO insulation material 156. Fuel from the fuel conduit 300C enters from the top of the central column 400. The fuel then bypasses the anode exhaust cooler 140 by flowing through the hollow core of the anode exhaust cooler 140, and then flows between the outer cylinder 110C and the corrugated plate 110B of the anode reconverter 110. The fuel then flows to the stack 102 through the hub base 602 and conduit 300D of the anode hub structure 600 shown in Figure 3B.

[0028] Referring to Figures 2A, 2B, 2C, 3A, and 3B, the fuel exhaust flows from the stack 102 through the anode exhaust conduit 308A to the hub base 602, from the hub base 602 through the anode reheater 110 between the inner cylinder 110A and the corrugated plate 110B, and through the anode exhaust conduit 308B into the splitter 158. As shown in Figure 1, the first portion of the fuel exhaust flows from the splitter 158 through the anode exhaust conduit 308C to the anode exhaust cooler 140, while the second portion flows from the splitter 158 through the anode exhaust conduit 308D to the ATO 150. An inner core insulation material 140A of the anode exhaust cooler can be located between the fuel conduit 300C and the bellows 852 / support cylinder 852A, where the bellows 852 / support cylinder 852A is located between the anode exhaust cooler 140 and the vortex generator 159, as shown in Figure 3A. This insulation material minimizes heat transfer and heat loss from the first portion of the anode exhaust flow in the anode exhaust conduit 308C on its way to the anode exhaust cooler 140. The insulation material 140A can also be located between the conduit 300C and the anode exhaust cooler 140 to avoid heat transfer between the fuel inlet flow in the fuel conduit 300C and the flow in the anode exhaust cooler 140. In other embodiments, the insulation material 140A can be omitted from within the cylindrical anode exhaust cooler 140.

[0029] Figure 3B also shows that air flows from air conduit 302A to the anode exhaust cooler 140 (where the air is heated by the first portion of the anode exhaust), and then from the anode exhaust cooler 140 through conduit 302B to the cathode reheater 500. The first portion of the anode exhaust is cooled in the anode exhaust cooler 140 by the air flowing through the anode exhaust cooler 140. The cooled first portion of the anode exhaust is then supplied from the anode exhaust cooler 140 to the anode recirculation blower 212 shown in Figure 1.

[0030] As described in more detail below and as shown in Figures 2A and 3B, the anode exhaust exits the anode reconverter 110 and is supplied into the splitter 158 through the anode exhaust conduit 308B. The splitter 158 divides the anode exhaust into a first and second part (i.e., flow). The first flow is supplied into the anode exhaust cooler 140 through the anode exhaust conduit 308C. The second flow is supplied to the ATO 150 through the anode exhaust conduit 308D.

[0031] The relative amounts of anode exhaust supplied to ATO150 and anode exhaust cooler 140 are controlled by anode recirculation blower 212. The faster the blower 212 is, the more anode exhaust is supplied into anode exhaust conduit 308C, and the less anode exhaust is supplied to ATO150 via anode exhaust conduit 308D, and vice versa. The anode exhaust supplied to ATO150 can be oxidized by stack cathode (i.e., air) exhaust and supplied to cathode reconverter 500 through conduit 304B.

[0032] Figure 4A is a cross-sectional view showing the air inlet baffle 550 located inside the cathode regenerator 500; Figure 4B is a simplified partial cross-sectional view showing the air and exhaust flow through the cathode regenerator 500, stack 102, and central column 400; and Figure 4C is a side view of the air inlet baffle 550.

[0033] Referring to Figures 4A to 4C, the cathode reconverter 500 can surround one or more of the stacks 102 and the central column 400, which is shown in detail in Figure 2A. The cathode reconverter 500 may comprise a cover 510 with an air inlet 510A and an air exhaust outlet 510B, an upper cover 514, an optional fin assembly 518, a lower cylinder 524, and an outer shell 528. The fin assembly 518 may comprise a cylindrical corrugated plate 520 and an inner wall 522 positioned inside the corrugated plate 520. The corrugated plate 520 may be configured to transfer heat between the incoming air and the outgoing cathode exhaust. The inner surface of the inner wall 522 may be covered with a thermal insulation material.

[0034] The annular air outlet 530 can be formed between the inner wall 522 and the lower cylinder 524. In particular, the air outlet 530 can be formed where the lower cylinder 524 and the inner wall 522 overlap. The annular ATO exhaust inlet 532 can be formed between the outer shell 528 and the lower cylinder 524.

[0035] As shown in Figures 4A and 4B, air enters the cathode regenerator 500 through the air inlet 510A, flows along the inner surface of the corrugated plate 520 beneath the upper cover 514, and can exit through the air outlet 530. The air then passes through the air inlet baffle 550 and can be supplied to the fuel cell stack 102 surrounded by the cathode regenerator 500. The cathode exhaust discharged from the stack 102 flows into the central column 400, is mixed with anode exhaust (not shown) in the vortex generator 159, and can then be supplied to the ATO 150. The ATO exhaust discharged from the ATO 150 (i.e., oxidized fuel exhaust) is supplied to the ATO exhaust inlet 532 of the cathode regenerator 500, flows along the outer surface of the corrugated plate 520, crosses the upper surface of the upper cover 514, and can then exit through the exhaust outlet 510B. Thus, the air is heated by the heat extracted from the ATO exhaust.

[0036] The air inlet baffle 550 is located inside the cathode regenerator 500 and can be a cylindrical component surrounding the fuel cell stack 102. The air inlet baffle can form a barrier between the cathode regenerator 500 and the fuel cell stack 102. The air inlet baffle 550 can be configured to control the flow of heated air to the fuel cell stack 102 in order to limit vertical temperature fluctuations along the height of the fuel cell stack 102 and optimize it to favorably achieve a uniform fuel utilization rate across the cells. For example, during steady-state operation of the system (which occurs after the system startup operation), the air inlet baffle 550 can be configured to result in vertical inter-cell temperature fluctuations in the fuel cell stack 102 of less than about 40°C, for example, between about 30°C and about 40°C. In some embodiments, during steady-state operation of the system, the air inlet baffle 550 can be configured to control the temperature of the fuel cell stack 102 such that the maximum fuel utilization rate of the fuel cells in the stack 102 exceeds the average fuel utilization rate of the entire fuel cell stack 102 by about 1% or less, for example, 0.1% to 1% above the average fuel utilization rate. In some embodiments, the air inlet baffle 550 can be configured to control the temperature of the stack 102 such that the fuel utilization rate of the fuel cells in the stack 102 is in the range of about 86% to about 91%. Thus, the difference between the minimum and maximum fuel utilization rates between two different fuel cells in the same stack is 10% or less, for example, 5% or less, for example, 4% to 6%.

[0037] The air inlet baffle 550 may comprise an array of openings 552 configured to direct heated air toward a specific portion of the stack 102. For example, in some embodiments, the openings 552 may be positioned on the air inlet baffle 550 such that the air inlet baffle directs more of the air discharged from the cathode reconverter 500 toward the top of the stack 102 than toward the bottom of the stack 102.

[0038] In some embodiments, the opening 552 can be a circular through-hole, as shown in Figure 4C. However, in other embodiments, the opening 552 can have other shapes, such as horizontal or vertical slits. The location, size, and / or number of the openings 552 can be set according to the desired stack 102 and / or system characteristics affected by the air supplied through the air inlet baffle 550.

[0039] In one embodiment, the air inlet baffle 550 does not have an opening 552 at the vertical level of the air outlet 530. Therefore, the air exiting the air outlet 530 collides with the continuous plate portion 553 of the air inlet baffle 550 and is not supplied directly to the fuel cell stack 102. Thus, a portion of the fuel cell stack 102 located at the vertical level of the air outlet 530 is not overcooled by the direct collision of the airflow supplied from the air outlet 530. Thus, the continuous plate portion 553 of the air inlet baffle 550 spreads (i.e., deflects) the air exiting the air outlet 530 vertically (i.e., up and down), and the air then reaches the fuel cell stack 102 through the opening 552. Thus, the air achieves a more uniform temperature by flowing vertically before reaching the stack 102. Furthermore, since the air collides with several vertical portions of the stack 102 located at the vertical level of the opening, no single region of the stack 102 is overcooled by the airflow. This results in a more uniform vertical temperature distribution along the height of stack 102.

[0040] Fuel supplied to the fuel cell flows from the bottom of the stack to the top of stack 102, and fuel exhaust from the fuel cell flows in the opposite direction through stack 102 via riser tubes or integrated fuel channels within the fuel cell stack 102. The fuel distribution may depend on the geometry of stack 102 and variations in the fuel properties associated with stack 102 due to local temperature fluctuations in stack 102. For example, higher fuel temperatures may increase fuel flow resistance, thus reducing fuel flow rate. Vertical stack temperature fluctuations may result from variations in heat generation by the fuel cell, convective cooling of the stack by incoming air, and radiative coupling between the stack and other heat-generating components of the SOFC system.

[0041] For example, Figure 5 is a simplified cross-sectional view showing the distribution of air from the cathode reconverter 500 to the stack 102 in a comparative fuel cell system without an air inlet baffle. As shown in Figure 5, the air exits the cathode reconverter 500 through the air outlet 530 and is first directed to the fuel cell in the central portion CP of the stack 102. As a result, the stack 102 may undergo a non-uniform vertical temperature profile due to the cooling of the fuel cell in the central portion CP by the incoming air.

[0042] In contrast, as described above with respect to Figures 4A to 4C, in one embodiment, a portion of the fuel cell stack 102 located at the vertical level of the air outlet 530 is not overcooled by the direct impact of the airflow supplied from the air outlet 530. Thus, the continuous plate portion 553 of the air inlet baffle 550 spreads (i.e., redirects) the air exiting the air outlet 530 vertically (i.e., up and down), and the air then passes through the opening 552 to reach the fuel cell stack 102. Thus, the air reaches a more uniform temperature by flowing vertically before reaching the stack 102. Furthermore, even when the opening 552 is at the vertical level of the air outlet 5230, no single region of the stack 102 is overcooled by the airflow because the air impacts several vertical portions of the stack 102 located at the vertical level of the opening 552. This results in a more uniform vertical temperature distribution along the height of the stack 102.

[0043] The inventors have found that reducing vertical temperature fluctuations within the stack can lead to better cell temperature control, voltage performance, and voltage uniformity across various operating conditions, thereby reducing cell degradation and thermal stress. In addition, an optimal vertical stack temperature profile improves the vertical uniformity of fuel flow to the fuel cell within the stack. Fuel cells may degrade and / or fail at excessively high fuel utilization rates due to fuel cell depletion. The maximum fuel utilization rate in the cells within the stack can be a determining factor in overall fuel utilization and system efficiency.

[0044] For example, referring again to Figure 4C, the numerous small-diameter openings 552 minimize pressure drop and parasitic losses caused by the air blower supplying air to the cathode regenerator 500. The numerous small-diameter openings 552 can also prevent and / or reduce direct impact of high-speed air jets on the stack 102, thereby reducing damage to the stack and allowing for smoother distribution of incoming air to the air inlet plenum surrounding the stack 102.

[0045] Accordingly, the number, diameter, and / or spacing of the openings 552 in each array 554, and / or the arrangement of the arrays 554 can be selected to provide desired stack characteristics such as the stack temperature profile and the corresponding fuel utilization rate. For example, the openings 552 of the air inlet baffle 550 can be arranged in one or more annular arrays 554 separated vertically from each other by continuous plate portions 553 that do not have openings. For example, the openings 552 can be arranged in a first array 554A, a second array 554B, a third array 554C, and a fourth array 554D. However, the disclosure is not limited to a specific number of arrays 554. For example, each array 554 may include at least one row of openings 552, e.g., 1 to 10 rows of openings 552, 2 to 8 rows of openings 552, or 2 to 5 rows of openings 552.

[0046] In some embodiments, the first array 554A and the second array 554B are positioned below the annular air outlet 530, and the third array 554C and the fourth array 554D are positioned above the annular air outlet 530. In some embodiments, the third array 554C and the fourth array 554D may include more rows of openings 552 than the first array 554A and the second array 554B, and the third array 554C may include more rows of openings 552 than the fourth array 554D. Thus, the air inlet baffle 550 can supply more airflow to the upper end of the stack than to the lower end.

[0047] The openings 552 can have a diameter in the range of approximately 2 mm to approximately 20 mm, for example, approximately 5 mm to approximately 15 mm. The openings 552 in each row can have a horizontal center-to-center spacing in the range of approximately 2 mm to approximately 20 mm, for example, approximately 5 mm to approximately 15 mm. The openings 552 in adjacent rows can have a vertical center-to-center spacing in the range of approximately 2 mm to approximately 20 mm, for example, approximately 5 mm to approximately 14 mm.

[0048] In some embodiments, the first array 554A can be positioned approximately 130 mm to 150 mm from the bottom of the air inlet baffle plate 550. The second array 554B can be positioned approximately 240 mm to 265 mm from the bottom of the air inlet baffle plate 550. The third array 554C can be positioned approximately 410 mm to 435 mm from the bottom of the air inlet baffle plate 550. The fourth array 554D can be positioned approximately 500 mm to 525 mm from the bottom of the air inlet baffle plate 550.

[0049] Initial column / stack fuel distribution (CFD) modeling predicts improved uniformity of fuel delivery through a linear temperature profile with a difference of approximately 20°C, where the temperature is higher at the bottom of the stack or column than at the top. To achieve high fuel utilization, low inter-cell fuel utilization variability, and high overall system efficiency in the fuel cell, the maximum fuel utilization in any cell within the stack should preferably be kept within approximately 1% of the average stack fuel utilization. Air inlet baffles can be designed to obtain a stack temperature profile with a slightly negative slope in the vertical direction (e.g., from the bottom to the top of the stack), thereby improving the vertical fuel distribution along the stack.

[0050] For example, more openings 552 can be located at the top of the air inlet baffle 550 than at the bottom of the air inlet baffle 550, thereby supplying more heated air to the top of the stack 102 located above the annular air outlet 530 than to the bottom of the stack 102 located below the annular air outlet 530, and maintaining the top of the stack 102 at a lower temperature than the bottom of the stack 102 and the middle section of the stack 102 located at the level of the annular air outlet 530. Furthermore, the bottom of the stack 102 can be maintained at a lower temperature than the middle section of the stack 102 located at the level of the annular air outlet 530.

[0051] Figure 6 is a graph showing the average vertical temperature profile of a lifetime initial (BOL) stack operating at 51 amperes, and the vertical temperature profile predicted based on the optimal cell fuel distribution (CFD), when used in a fuel cell system equipped with the air inlet baffle shown in Figure 4C.

[0052] Referring to Figure 6, each stack tested contained 256 fuel cells numbered sequentially, with cell 1 located at the bottom of the stack and cell 256 at the top. The temperatures from cell 1 to approximately cell 32 can gradually increase, with cell 1 having the lowest temperature and cell 32 having the highest. The temperatures from cells 33 to 224 can gradually decrease at a relatively constant rate, with cell 33 having the highest temperature and cell 224 having the lowest, thereby having a substantially linear negative slope for the vertical temperature gradient from cells 33 to 224. The air inlet baffle plate was shown to result in a vertical stack temperature profile that roughly matches the predicted temperature profile. Therefore, the air inlet baffle plate results in an improvement in fuel distribution.

[0053] Figure 7 is a graph showing the average vertical fuel utilization profile of a stack tested under 51 amperes of BOL operating conditions. Referring to Figure 7, the graph shows that the maximum fuel utilization of a cell in the stack is 91%, which is within 1% of the average stack fuel utilization of 90%. Thus, the air inlet baffle design is shown to strictly maintain both the vertical fuel utilization spread and the heat distribution.

[0054] Figure 8 is a graph showing the average vertical temperature profiles of an early-life (BOL) stack operating at 51 amps and a mid-life (MOL) stack operating at 66 amps (e.g., under degraded cell conditions) when used in a fuel cell system equipped with the air inlet baffle shown in Figure 4C. As can be seen in Figure 6, the air inlet baffle strictly maintains vertical heat distribution at higher currents and degraded cell conditions. In addition, although the thermal profile shifted to a lower temperature for the 66-amp MOL operation, the slope and nature of the temperature profile roughly matched those of the 51-amp BOL profile, thus indicating an improvement in fuel distribution.

[0055] The above-described embodiments of the disclosure are provided to enable those skilled in the art to practice 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 can be applied to other embodiments without departing from the scope of the invention. Accordingly, the present invention is not intended to be limited to the embodiments shown herein, but rather to be given the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. Fuel cell stack and A cathode reheater having an annular air outlet configured to heat air using cathode exhaust discharged from the stack and to discharge the heated air radially inward in the horizontal direction toward the stack, An air inlet baffle positioned between the cathode reheater and the stack and extending annularly around the stack, comprising at least two rows of openings arranged horizontally, the at least two rows of openings being separated vertically, and configured to supply the heated air discharged from the cathode reheater radially inward in the horizontal direction to multiple regions of the stack, A fuel cell system equipped with the following features.

2. The system according to claim 1, wherein during steady-state operation of the system, the air inlet baffle is configured to control the vertical temperature profile of the stack such that the temperature fluctuation between fuel cells is 40°C or less.

3. The system according to claim 1, wherein during steady-state operation of the system, the air inlet baffle is configured to control the vertical temperature profile of the stack such that the maximum fuel utilization rate of any given fuel cell in the stack exceeds the average fuel utilization rate of the stack of fuel cells by about 1% or less.

4. The system according to claim 3, wherein during steady-state operation of the system, the fuel cell has a fuel utilization rate in the range of 86% to 91%, and the fuel cell includes a solid oxide fuel cell.

5. The opening is a through-hole having a diameter in the range of 5 mm to 15 mm, passing through the continuous plate portion of the air inlet baffle. The system according to claim 1, wherein adjacent openings in each row are separated by a center-to-center distance in the range of 5 mm to 15 mm.

6. The aforementioned air inlet baffle is cylindrical, The system according to claim 1, wherein the air inlet baffle is configured to redirect the heated air discharged from the annular air outlet vertically.

7. The openings are arranged as an array extending around the circumference of the air inlet baffle, The system according to claim 6, wherein each array includes at least two rows of the openings.

8. The openings are arranged in the first array, the second array, the third array, and the fourth array. The first array and the second array are arranged below the annular air outlet. The system according to claim 7, wherein the third and fourth arrays are positioned above the annular air outlet.

9. A fuel cell stack, A cathode reheater configured to heat air using cathode exhaust discharged from the stack, Displaced between the cathode reheater and the stack, and comprising at least two rows of openings arranged horizontally, the at least two rows of openings being separated vertically, and configured to supply heated air discharged from the cathode reheater to multiple regions of the stack, A fuel cell system comprising, The aforementioned air inlet baffle is cylindrical, The cathode reheater is provided with an annular air outlet configured to discharge the heated air horizontally toward the stack, The air inlet baffle is configured to redirect the heated air discharged from the annular air outlet vertically. The openings are arranged as an array extending around the circumference of the air inlet baffle, Each array includes at least two rows of the openings, The openings are arranged in the first array, the second array, the third array, and the fourth array. The first array and the second array are arranged below the annular air outlet. The third and fourth arrays are positioned above the annular air outlet. A system wherein the third and fourth arrays include a larger number of the openings than the first and second arrays.

10. The continuous plate portion of the air inlet baffle is located at the vertical level of the annular air outlet. The air inlet baffle does not have the opening at the vertical level of the annular air outlet. The system according to claim 6, wherein the continuous plate portion of the air inlet baffle is configured to redirect the heated air discharged from the annular air outlet vertically.

11. To supply heated air and fuel to the fuel cell stack, The stack is operated in a steady-state mode to discharge fuel exhaust and cathode exhaust, The fuel exhaust and the cathode exhaust are supplied to an anode tail gas oxidizer that oxidizes the fuel exhaust. The exhaust gas from the anode tail gas oxidizer is supplied to the cathode reheater, Supplying air to the cathode reheater, Heat the air using the exhaust from the anode tail gas oxidizer, including the cathode exhaust from the stack, and discharge the heated air from the annular air outlet of the cathode reheater to an air inlet baffle, which is located between the cathode reheater and the stack, radially inward in the horizontal direction toward the stack, and extends annularly around the stack, having at least two rows of openings arranged horizontally, the at least two rows of openings separated along the vertical direction. To supply the heated air to multiple regions of the stack through the at least two rows of openings in the radially inward direction in the horizontal direction, including, How to operate a fuel cell system.

12. The method according to claim 11, wherein, during the steady-state mode, the air inlet baffle controls the vertical temperature profile of the stack such that the temperature fluctuation between fuel cells is 40°C or less.

13. The method according to claim 11, wherein, during operation in the steady-state mode, the air inlet baffle controls the vertical temperature profile of the stack such that the maximum fuel utilization rate of any fuel cell in the stack exceeds the average fuel utilization rate of the stack of fuel cells by about 1% or less.

14. The method according to claim 13, wherein during operation in the steady-state mode, the fuel cell has a fuel utilization rate in the range of 86% to 91%.

15. The opening is a through-hole having a diameter in the range of 5 mm to 15 mm, passing through the continuous plate portion of the air inlet baffle. The method according to claim 11, wherein adjacent openings in each row are separated by a center-to-center distance in the range of 5 mm to 15 mm.

16. The aforementioned air inlet baffle is cylindrical, The method according to claim 11, wherein the air inlet baffle redirects the heated air discharged from the annular air outlet vertically.

17. The openings are arranged as an array extending around the circumference of the air inlet baffle, The method according to claim 16, wherein each array includes at least two rows of the openings.

18. Supplying heated air and fuel to the stack of a fuel cell, The stack is operated in a steady-state mode to discharge fuel exhaust and cathode exhaust, The fuel exhaust and the cathode exhaust are supplied to an anode tail gas oxidizer that oxidizes the fuel exhaust. The exhaust gas from the anode tail gas oxidizer is supplied to the cathode reheater, Supplying air to the cathode reheater, The air is heated using the exhaust from the anode tail gas oxidizer, including the cathode exhaust from the stack, and the heated air is discharged from the cathode reheater onto an air inlet baffle located between the cathode reheater and the stack, comprising at least two rows of openings arranged horizontally, the at least two rows of openings separated vertically. The heated air is supplied to multiple regions of the stack through the at least two rows of openings, A method for operating a fuel cell system including, The aforementioned air inlet baffle is cylindrical, The cathode reheater is equipped with an annular air outlet that discharges the heated air horizontally toward the stack, The air inlet baffle redirects the heated air discharged from the annular air outlet vertically. The openings are arranged as an array extending around the circumference of the air inlet baffle, Each array includes at least two rows of the openings, The openings are arranged in the first array, the second array, the third array, and the fourth array. The first array and the second array are arranged below the annular air outlet. The third and fourth arrays are positioned above the annular air outlet. The method wherein the third and fourth arrays include more openings than the first and second arrays so that more heated air is supplied to the upper part of the stack than to the lower part of the stack.

19. The continuous plate portion of the air inlet baffle is located at the vertical level of the annular air outlet. The air inlet baffle does not have the opening at the vertical level of the annular air outlet. The method according to claim 16, wherein the continuous plate portion of the air inlet baffle redirects the heated air discharged from the annular air outlet toward the opening vertically.

20. Supplying heated air and fuel to the stack of a fuel cell, The stack is operated in a steady-state mode to discharge fuel exhaust and cathode exhaust, The fuel exhaust and the cathode exhaust are supplied to an anode tail gas oxidizer that oxidizes the fuel exhaust. The exhaust gas from the anode tail gas oxidizer is supplied to the cathode reheater, Supplying air to the cathode reheater, The air is heated using the exhaust from the anode tail gas oxidizer, including the cathode exhaust from the stack, and the heated air is discharged from the cathode reheater onto an air inlet baffle located between the cathode reheater and the stack, comprising at least two rows of openings arranged horizontally, the at least two rows of openings separated vertically. The heated air is supplied to multiple regions of the stack through the at least two rows of openings, A method for operating a fuel cell system including, The aforementioned air inlet baffle is cylindrical, The cathode reheater is equipped with an annular air outlet that discharges the heated air horizontally toward the stack, The air inlet baffle redirects the heated air discharged from the annular air outlet vertically. The continuous plate portion of the air inlet baffle is located at the vertical level of the annular air outlet. The air inlet baffle does not have the opening at the vertical level of the annular air outlet. The continuous plate portion of the air inlet baffle redirects the heated air discharged from the annular air outlet toward the opening vertically. A larger volume of heated air is supplied to the upper part of the stack, which is located above the annular air outlet, than to the lower part of the stack, which is located below the annular air outlet. A method wherein the upper part of the stack is maintained at a lower temperature than both the lower part of the stack and the middle part of the stack located at the vertical level of the annular air outlet.

Images