SOFC-Conduction

Abstract

To provide an improved SOFC system for thermal energy management. A primary enclosure wall assembly (8045) for temperature balancing includes a combustion region wall defining a cathode chamber (8055) in which a SOFC stack (8005) is disposed and a first sidewall extending from the combustion region wall along a gas flow axis. Heat generated in the combustion region around the outlet end of the SOFC stack is transferred to the combustion region wall. A cathode input manifold (9070) is disposed outside the primary enclosure wall assembly, the wall including the combustion region wall and the first sidewall, the inner surface of the first sidewall defining the cathode chamber, the outer surface of the first sidewall facing the cathode input manifold. Heat absorbed by the combustion region wall is thermally conducted to the distal end of the first sidewall, and the heat is radiated from the inner surface of the first sidewall through the cathode chamber to the inlet end of the SOFC stack to the outer surface of the cells of the SOFC stack. The heat is then transferred by convection and radiation to the cathode airflow in the cathode input manifold, lowering the temperature of the combustion region wall and raising the surface temperature of the first sidewall.

Description

[Technical Field]

[0001] Exemplary specific technology herein relates to solid oxide fuel cell (SOFC) systems, methods of use, and methods of manufacturing SOFC systems. In particular, exemplary specific technology relates to improved systems and methods for thermal energy management within SOFC systems. [Background technology]

[0002] Conventional SOFC systems include a hot zone that includes or at least partially surrounds system components maintained at higher operating temperatures (e.g., greater than 350°C or 500°C during operation, depending on the SOFC technology). The hot zone houses the SOFC energy generator or solid oxide fuel cell stack. A conventional SOFC fuel cell stack is formed by one or more fuel cells, each participating in an electrochemical reaction that generates electrical current. The fuel cells are electrically interconnected in series or parallel as needed to provide the desired output voltage of the cell stack. Each fuel cell includes three primary layers: an anode layer or fuel electrode, a cathode layer or air electrode, and an electrolyte layer that separates the anode layer from the cathode layer.

[0003] The anode layer is exposed to a gaseous or vaporous fuel containing at least hydrogen gas (H2) and / or carbon monoxide (CO). At the same time, the cathode layer is exposed to a cathode gas or vaporous oxygen (O2) source, such as air or other gas. At the cathode layer, the oxygen (air) supplied to the cathode layer accepts electrons and forms oxygen ions (O -2) Oxygen ions pass from the cathode layer through the ceramic electrolyte layer to the anode layer. At the three-phase boundary, hydrogen (H2) and / or carbon monoxide (CO) supplied to the anode layer by the fuel react with the oxide ions to produce water and carbon dioxide, and electrons released during this reaction produce electricity and heat. Other reaction products in the fuel stream may include methane, ethane, or ethylene. Electricity produced by the electrochemical reaction is drawn off to the DC power terminals to power an electrical load.

[0004] Common anode materials include cermets such as nickel-doped zirconia (Ni-YSZ), nickel-doped ceria (Ni-SDC and / or Ni-GDC), and copper-doped ceria. 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3-δ Perovskite anode materials such as lanthanum strontium cobalt oxide (LSCM) and other ABO3 structures can also be used. Common cathode materials include lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), and lanthanum strontium manganite (LSM). The electrolyte layer is an ion-conducting ceramic, typically an oxygen-ion conductor such as yttria-doped zirconia or gadolinium-doped ceria. Alternatively, the electrolyte layer can be a proton-conducting ceramic such as barium cerate or barium zirconate. The electrolyte layer acts as a nearly hermetic barrier to prevent the fuel and air from mixing and burning. Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional SOFC systems use cross-flow or parallel-flow heat exchangers, commonly called recuperators, to heat the cathode gas (air) entering the SOFC system. The gas-flow heat exchanger heats the cold air entering the hot zone by exchanging thermal energy between the cold air entering the hot zone and the hot exhaust gas exiting the hot zone. Air-to-air cross-flow heat exchangers are inefficient compared to heat energy transfer via conduction. Conventional SOFC power generation systems rely heavily on the incoming cathode air flow to manage thermal energy distribution. However, the cathode air flow rate is traditionally selected to redistribute thermal energy rather than to optimize the SOFC reaction. When selecting the volumetric or mass flow rate (e.g., liters / second) of cathode air to optimize the SOFC reaction, the required volumetric or mass flow rate is significantly less than that required to redistribute thermal energy. In some cases, the distribution of thermal energy requires a cathode air flow rate 300% greater than that required for the SOFC reaction. One consequence of using higher volumetric airflow rates in SOFC systems is a decrease in power generation efficiency due to the energy required to move the excess airflow. Also, the thermal energy used to heat the excess airflow is unavailable to heat the SOFC stack and other surfaces, especially during start-up.

[0006] In conventional SOFC systems, a recuperator, or gas counterflow heat exchanger, is positioned to receive the hot gases exiting the tail gas combustion chamber and the cold gases entering the SOFC system in counterflow conduits separated by a common wall. Again, convection and radiation are the primary heat energy transfer mechanisms as the hot gases from the combustor heat conduit walls pass to the exit port, where they heat the incoming air. In short, heat energy exchange within both the tail gas combustion chamber and the recuperator is inefficient. As a result, conventional SOFC systems are notoriously difficult to control, often resulting in hot spots within the combustion enclosure, for example, that can become too hot and even burn through the walls, potentially damaging the enclosure walls. Alternatively, when the temperature of an SOFC system is reduced, for example by reducing the fuel input flow rate and increasing the input cathode air flow rate to cool hot spots, the SOFC reactions can change, often leading to undesirable behavior such as reduced power output, incomplete fuel processing resulting in carbon formation on the anode surface, which ultimately leads to reduced electrical output and eventual failure.

[0007] To adequately address hot and cold spots, conventional SOFC systems often include multiple thermocouples or thermistors placed at various system points to monitor temperatures and adjust operation to avoid hot spots and prevent cold spots. However, temperature sensing and monitoring systems are costly and prone to failure due to the high operating temperatures of SOFC systems (e.g., 350–1200°C near the tail gas combustion chamber). Furthermore, the need to adjust fuel input as a means to avoid SOFC system damage leads to inefficient and fluctuating power output. Therefore, there is a need in the art to avoid temperature gradients and eliminate hot spots to avoid SOFC system damage, deliver more stable power output, and improve power generation efficiency. There is also a need to provide a more efficient, passive method for thermal energy management in SOFC systems that does not rely on modifying fuel and air flow rates to manage thermal energy distribution, for example, to reduce hot spot temperatures.

[0008] Conventional SOFC systems use heat- and corrosion-resistant materials to withstand the effects of prolonged operation at high temperatures and the harsh corrosive environment that continually oxidizes metal surfaces, sometimes to the point of destruction. The use of specialized high-temperature, corrosion-resistant nickel-chromium alloys, such as Inconel, Monel, and Hastelloy, is common in SOFC systems. However, while these materials perform well in the high-temperature, corrosive environment of SOFC generators, they tend to have very low thermal conductivity coefficients compared to materials with higher thermal conductivity, such as copper, aluminum, or molybdenum. As an example, the thermal conductivity of Inconel ranges from 17 to 35 W / (m·K) over a temperature range of 150 to 875 °C, compared to copper, which has a thermal conductivity ranging from approximately 370 W / (m·K) at 500 °C to 332 W / m·K at 1027 °C. Thus, the thermal conductivity of copper is more than 10 times that of Inconel. Although copper offers higher thermal conductivity than high-temperature non-corrosive metal alloys, copper is highly susceptible to breakdown by oxidation at high temperatures and has therefore been avoided so far as a material for SOFC enclosures. [Means for solving the problem]

[0009] The present technology overcomes problems associated with conventional SOFC systems by providing various embodiments of improved SOFC systems, including configurations of a hot zone enclosure assembly (8042) formed by a U-shaped primary enclosure wall assembly (8045) and a hot zone enclosure assembly (12042) including two L-shaped primary enclosure wall assemblies (12045), as well as other hot zone enclosure assembly embodiments (14042, 15042) utilizing one or more U-shaped and L-shaped primary enclosure wall assemblies. Each primary enclosure wall assembly is formed to enclose a SOFC stack (8005), a cathode chamber (8055, 12055), and a combustion region (8030) located above the fuel output end (8025) of each individual fuel cell. Each primary enclosure wall assembly includes a combustion region wall (8060, 12060) formed to bound the combustion region and at least one opposing primary enclosure side wall (8065, 8070, 12070) each extending from an edge of the combustion region wall (8060, 12060) to the cathode input end of an individual fuel cell, such that the SOFC stack is surrounded by the primary enclosure wall assembly along at least the entire longitudinal length (x) of the SOFC stack along the input end (8020).

[0010] Each primary enclosure wall (8060, 12060), (8065), and (8070, 12070) includes a thermally conductive core (8200) protected from oxidation by an outer layer applied to its exposed surface. The thermally conductive core (8200) includes one or more materials having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K). The thermally conductive core is formed from copper or molybdenum, or an aluminum-copper or copper-nickel alloy, or a combination thereof. The thickness of the thermally conductive core ranges from 0.127 to 6.0 mm (0.005 to 0.24 in).

[0011] To prevent oxidation of the thermally conductive core (8200), each of the core segments (8205, 8210, 8215, 12010, 12015, 12017) is protected by a protective layer applied over or attached to the exposed surface of the thermally conductive core. The protective layer may include a nickel plating applied to the surface of each core segment by an electroplating process to a thickness ranging from at least 0.0005 inches to a maximum of 0.002 inches. Alternatively, or additionally, the protective layer may include one or more metal sheets positioned in mating contact with each exposed surface of the three core segments (8205), (8210, 12010), and (8215, 12015, 12017). The metal sheets may be applied directly to the uncoated surface of the thermally conductive core or to the electroplated surface of the thermally conductive core. The inner protective sheet metal layer (8220) is fabricated as a U-shaped structure formed to adhere to the inner surfaces of each of the three core sections (8205), (8210), and (8215), with the inner surface of the inner protective layer (8220) facing the SOFC stack. The outer protective layer (8250) includes two substantially identical outer sidewall sections (8255) and (8260) and an outer top section (8265). When the three outer protective layer sections are bonded together and with the corresponding outer surfaces of the thermally conductive core, they form a U-shaped sheet metal structure shaped to attach to the outer surface of the thermally conductive core (8200) and protect the outer surface of the thermally conductive core (8200) from exposure to the oxygen-rich cathode airflow. Preferably, the inner surface of the outer protective layer is in mating contact with the corresponding outer surface of the thermally conductive core facing away from the SOFC stack. A second embodiment of the inner protective layer (12220) and the outer protective layer (12250) is also described herein.

[0012] The wall portions of each of the inner and outer protective layers are fabricated from a ferritic steel, such as Alloy 18 SR® stainless steel, available from Rolled Metal Products, Alsip, Illinois. Alloy 18 SR® stainless steel is an aluminum-stabilized ferritic stainless steel designed for high-temperature applications, with improved scaling and corrosion resistance achieved through the addition of aluminum in the range of 1.5 to 2.5 weight percent. Alloy 18 SR® stainless steel is preferred because, under the operating temperatures and conditions of SOFC systems (8000), the added aluminum content advantageously forms an aluminum oxide surface layer that prevents oxidation of the exposed surfaces of the inner and outer protective layers, which prevents oxidation and leaching of chromium from Alloy 18 SR® stainless steel.

[0013] Each hot zone enclosure assembly (8042, 12042, 14042, 15042) optionally includes end walls (8080, 8085) and a bottom wall (8075) that further surround the cathode chamber (8055, 12055), or the cathode chamber is further surrounded by an intermediate enclosure (9000) that includes end walls (9020, 9025) and a bottom wall (9010). The end walls (8080, 8085) and base wall (8075) can include a thermally conductive core with a protective layer provided to prevent oxidation damage to the core material.

[0014] The configuration of the present technology will be best understood from the exemplary embodiments thereof selected for purposes of detailed description and illustration of the technology and illustrated in the accompanying drawings. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows a schematic diagram of a first exemplary SOFC system according to the present technique. [Figure 2] 1 shows a schematic diagram of an exemplary hot zone of a SOFC system according to the present technology. [Figure 3]1 shows a schematic diagram of an exemplary fuel flow path of a SOFC system according to the present technique. [Figure 4] 1 shows a schematic diagram of an exemplary air flow path of a SOFC system according to the present technique. [Figure 5A] 1 shows a cross section through a first exemplary hot zone outer wall of a SOFC system according to the present technique. [Figure 5B] 1 shows a cross section through a second exemplary hot zone outer wall of a SOFC system according to the present technique. [Figure 5C] 1 shows a cross section through an exemplary bottom tube support wall including a thermally conductive mass of a SOFC system according to the present technology. [Figure 5D] 1 shows a cross section through an exemplary combustion section end wall including thermally conductive masses of a SOFC system according to the present technique. [Figure 5E] 1 shows a cross section through an exemplary combustion zone bottom wall including a thermally conductive mass of a SOFC system according to the present technology. [Figure 6] 1 shows a schematic cross-sectional top view of a SOFC system having multiple rod-shaped fuel cells arranged in two concentric circular patterns according to the present technology. [Figure 7A] 1 shows a schematic diagram of a first improved fuel cell system including a first U-shaped primary enclosure wall assembly disposed on a single SOFC stack in accordance with the present technique; [Figure 7B] 7A is a schematic diagram of a first improved fuel system in accordance with the present technique, with dashed lines with arrows indicating syngas flow and conductive heat flow through the U-shaped primary enclosure, and solid lines with arrows indicating cathode gas flow and radiative emissions from the high temperature region. [Figure 8A] FIG. 1 shows an isometric view of an intermediate enclosure of a hot zone assembly in accordance with the present technology. [Figure 8B] FIG. 1 shows a cross section through a primary enclosure wall assembly in accordance with the present technology. [Figure 9A] 1 shows an isometric side view of an improved hot zone configuration in accordance with the present technology. [Figure 9B] 1 shows a detailed isometric side view of a cathode flow passage for receiving a cathode within a hot zone enclosure assembly according to the present technique. [Figure 9C] FIG. 1 shows an exploded isometric view of a primary enclosure assembly in accordance with the present technology. [Figure 10A] Test Fixture FIG. 1 shows a schematic of the SOFC stack test fixture used to measure fuel cell temperature at five points along the SOFC stack axis when the fuel cell is operated to produce a DC current output. [Figure 10B] The graph shows a comparison of fuel cell temperatures at five points along the SOFC stack axis when the test fixture is operated without a thermally conductive core (shown in black) and when the test fixture is operated with a thermally conductive core layer installed (shown in diagonal lines). [Figure 11A] 10 graphically illustrates temperature measurements at five locations along the SOFC stack axis over a 2.5 hour start-up and shutdown cycle without the use of the thermally conductive core of the present technology. [Figure 11B] 10 graphically illustrates temperature measurements at five locations along the SOFC stack axis over a 2.5 hour start-up and shutdown cycle using the thermally conductive core of the present technology. [Figure 12] 1 illustrates a schematic diagram of a fuel cell system including a T-shaped primary enclosure wall assembly disposed on two SOFC stacks according to an embodiment of the present technology. [Figure 13] FIG. 1 shows an isometric side view of a hot zone enclosure assembly including two halves of a T-shaped primary enclosure wall, each half surrounding a SOFC stack and other cathode chamber portions, according to one embodiment of the present technology. [Figure 13A] FIG. 14 shows an isometric side view of an assembled L-shaped primary enclosure wall assembly in accordance with an aspect of the present technology. [Figure 13B] FIG. 14 shows an exploded isometric side view of one half of a T-shaped primary enclosure wall assembly in accordance with an aspect of the present technology. [Figure 14] 1 illustrates a schematic diagram of a fuel cell system including an L-shaped primary enclosure wall assembly disposed on one SOFC stack, according to one aspect of the present technique. [Figure 15]1 illustrates a schematic diagram of a fuel cell system including two SOFC stacks each surrounded by a U-shaped primary enclosure wall assembly, according to one aspect of the present technology. [Figure 16A] FIG. 16 shows a side isometric view of an outer enclosure for enclosing the hot zone assembly of FIGS. 12, 14, and 15 in accordance with an aspect of the present technology. [Figure 16B] FIG. 16 shows an exploded side isometric view of an outer enclosure and an intermediate enclosure for enclosing the hot zone assembly of FIGS. 12, 14, and 15 in accordance with an aspect of the present technology. [Figure 17] FIG. 16 shows an exploded side isometric view of an intermediate enclosure for enclosing the hot zone assembly of FIGS. 12, 14, and 15 in accordance with an aspect of the present technology. DETAILED DESCRIPTION OF THE INVENTION

[0016] definition Unless otherwise stated, the following definitions are used throughout: [Table 1]

[0017] Unless otherwise stated, the following symbols are used throughout: [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4]

[0018] Referring to FIG. 1, a schematic diagram of a first embodiment of the present technology illustrates a solid oxide fuel cell (SOFC) system (100). The system (100) includes a hot zone (105) containing at least one SOFC fuel cell, preferably multiple fuel cells forming an SOFC stack maintained at an elevated operating temperature, and a cold zone (110) containing a fuel input and exhaust module, a DC power output module, and other control elements. A hot zone enclosure wall (115) is positioned to enclose a hot zone cavity (120) therein. A thermal insulation layer (130) surrounds the enclosure wall (115) and insulates the hot zone (105). An air gap (125) is provided between the thermal insulation layer (130) and the sidewall of the hot zone enclosure wall (115), providing a gas flow conduit for gas to flow over the exterior surface of the hot zone enclosure wall.

[0019] According to an important aspect of the present technology, the hot zone enclosure walls (115) and associated thermal energy management elements described below are in thermal communication with one another to provide a heat conduction path for the transfer of thermal energy to all regions of the hot zone by heat conduction through the hot zone enclosure walls (115). More specifically, the hot zone enclosure walls (115) and any thermal energy management elements described below comprise a material having a high thermal conductivity coefficient, e.g., 100-300 W / (m·K), preferably greater than 200 W / (m·K), at temperatures ranging from 350-1200°C. Accordingly, the hot zone enclosure outer walls and other thermal energy management elements described below are fabricated from one or more of copper, molybdenum, aluminum-copper, copper-nickel alloy, or combinations thereof. Specifically, the hot zone enclosure walls (115) and associated thermal energy management elements are configured to provide a heat conduction path for the rapid transfer of thermal energy from one region of the hot zone to another. More specifically, the hot zone enclosure walls (115) and associated thermal energy management elements are configured to manage thermal energy within the hot zone by rapidly conducting thermal energy from higher temperature regions of the hot zone to lower temperature regions of the hot zone, such that the entire hot zone is maintained at a more uniform temperature than is typical in conventional SOFC systems.

[0020] An electrochemical energy generator or fuel cell stack (135), including one or more solid oxide fuel cells (SOFCs) or other types of fuel cells, is enclosed within the hot zone (105) and supported against the enclosure walls (115) by one or more support elements, described below. The fuel cell stack (135) includes one or more fuel cells, each participating in an electrochemical reaction that generates an electric current. The fuel cells are electrically interconnected in series or parallel as needed to provide the desired output voltage for the cell stack (135). Each fuel cell includes three primary layers: an anode layer or fuel electrode (150), a cathode layer or air electrode (155), and an electrolyte layer (145) that separates the anode layer from the cathode layer.

[0021] The anode layer (150) is exposed to a reactant, such as a gaseous or vaporous reformate containing at least hydrogen gas (H) and / or carbon monoxide (CO). At the same time, the cathode layer (155) is exposed to a source of air or vaporous oxygen (O) or any other oxidizing gas. At the cathode layer (155), oxygen (air) supplied to the cathode layer accepts electrons and forms oxygen ions (O -2 ) The cathode reaction is 1 / 2O2 + 2e - =O -2 and O II It is sometimes written as:

[0022] Oxygen ions pass from the cathode layer through the electrolyte layer (145) to the anode layer (150). In the anode layer, hydrogen (H2) and / or carbon monoxide (CO) supplied to the anode layer by the fuel react with the oxide ions to produce water and carbon dioxide, with electrons released during this reaction producing electricity and heat. The electricity produced by the electrochemical reaction is drawn off to the DC current output terminals (140) to power an electrical load.

[0023] Common anode materials include cermets such as nickel-doped zirconia, nickel-doped ceria, and copper-ceria. 1-x Mn x MoO 6-δ or La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3-δPerovskite anode materials such as lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), and lanthanum strontium manganite (LSM) can also be used. Common cathode materials include lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), and lanthanum strontium manganite (LSM). The electrolyte layer is an ion-conducting ceramic, typically an oxygen-ion conductor such as yttria-doped zirconia or gadolinium-doped ceria. Alternatively, the electrolyte layer is a proton-conducting ceramic such as barium cerate or barium zirconate. The electrolyte layer acts as a nearly hermetic barrier to prevent the fuel and air from mixing and combusting. The electrolyte layer acts as a nearly hermetic barrier to prevent the fuel and air from mixing and combusting.

[0024] Typically, each fuel cell is constructed with one of an anode layer (150), a cathode layer (155), or an electrolyte layer (145) formed as a support or mechanical structural element, with the other two layers coated onto the support element by, for example, dipping, spraying, etc. A variety of support element configurations are available, including one non-limiting exemplary embodiment shown in Figure 2, in which each fuel cell includes an anode support element configured as a hollow tube forming a cylindrical gas conduit, with the anode layer (150) forming the inner diameter of the cylindrical conduit, a ceramic electrolyte layer (145) coated on the outer diameter of the structural anode layer (150), and a cathode layer (155) coated on the outer diameter of the electrolyte layer (145).

[0025] Fuel, including at least hydrogen (H) and / or carbon monoxide (CO), flows through a hollow ceramic tube in contact with the anode layer, and air flows over and around the surface of the hollow tube in contact with the cathode layer. Electric current is generated as described above.

[0026] While the particular cell stack of Figure 2 includes multiple tubular fuel cells, other cell stacks formed with fuel cells having different known form factors can be used without departing from the present technology, including a fuel cell stack (135) formed from multiple flat sheet fuel cells formed in a stack, each cell including a support layer in sheet form with other layers coated on the support layer, and separators disposed between adjacent flat support layers with other layers coated on the support layer.

[0027] The supply fuel input line (160) delivers a supply fuel (8050) comprising a gaseous or vaporized hydrocarbon fuel received from a supply fuel container stored in the cold zone (110) or an external supply fuel source. A supply fuel delivery controller (197), in communication with the electronic controller (190), is disposed along the supply fuel input line (160) within the cold zone to control the supply fuel input rate and adjust the supply fuel input volume or mass flow rate as needed to mix the supply fuel with air. The supply fuel input line (160) delivers a supply fuel-air mixture (2025) to a fuel reformer (165) for fuel processing. The supply fuel-air mixture (2025) flows to the fuel reformer (165), which cracks the mixture (2025) to form a reformate, hereafter referred to as fuel (2027). The fuel (2027) is a reactant suitable for chemical reaction with the anode surface of the SOFC stack. The fuel (2027), or reformate, typically contains a mixture of H, CO, CO, and H0 with trace amounts of CH and other hydrocarbons. Other reformate contents may include methane, ethane, or ethylene. In an alternative embodiment, the feed fuel (8050) contains primarily hydrogen (H) with few or no additional components, and a reformer (165) is not required. Fuel received from a fuel reformer or directly from a feed fuel source passes over the surface of the anode layer (150) for electrochemical reaction with the anode layer (150).

[0028] The cathode gas input line (170) delivers gaseous or vaporous oxygen, such as ambient air or another oxygen source, to the cold zone (110) via, for example, an intake fan. An air delivery controller (198) in communication with the electronic controller (190) is optionally disposed along the cold zone air input line (170) to adjust the air input volume or mass flow rate as needed. The air input line (170) delivers room temperature air to a recuperator (175), which heats the input air by thermal energy exchange between hot gases exiting the hot zone and the incoming cold air. The heated incoming air passes over the surface of the cathode layer (155) for chemical reaction with the cathode layer (155).

[0029] Both the spent fuel and oxygen-depleted air exit the fuel cell stack (135) and mix within a combustion zone or tail gas combustor (180). The mixture of unreacted fuel and unreacted air delivered to the tail gas combustor (180) spontaneously ignites therein, generating localized thermal energy. The combustor walls, described in detail below, comprise a material having a high thermal conductivity coefficient, e.g., 100-300 W / (m·K), preferably greater than 200 W / (m·K). The combustor walls are also in thermal communication with the hot zone enclosure wall (115) so that thermal energy generated by combustion within the combustor (180) heats the combustor walls to a high temperature, which rapidly initiates thermal energy transfer to all regions of the hot zone via conductive thermal energy transfer through the hot zone enclosure wall (115).

[0030] Combustion by-products exiting the tail gas combustor (180), including hot gases, are delivered to a recuperator (175). The recuperator includes a cross-flow heat exchanger with counter-flow conduits provided to transfer thermal energy from the hot combustion by-products to cooler incoming air, thereby heating the incoming air before it enters the SOFC fuel cell stack (135). After passing through the recuperator (175), the combustion by-products are exhausted through an exhaust port (185).

[0031] Thermocouples or other temperature sensors (157) are attached to the surface of the enclosure wall (115) to sense its temperature, and the temperature information is communicated to an electronic controller (190). The controller (190) is in communication with other electronic elements, such as one or more electrically operable gas flow valves, gas flow detectors and / or modulators, coupled to a supply fuel delivery controller (197), or an air delivery controller (198), and a power output detector, and other elements that may be required to control various operating parameters of the SOFC (100). The electronic controller (190) monitors the DC current output and the temperature measured by the thermocouples, and further operates to vary the supply fuel input and air flow rate as a means of controlling the temperature.

[0032] An optional cold start module (195) can also be provided to preheat the input fuel supply and / or air during start-up. The cold start module (195) can be a fuel supply igniter that can be used to ignite a portion of the fuel supply to preheat the enclosure walls, and either the SOFC or the cold start module (195), or both, can include an electric heater that can be used to preheat the input fuel.

[0033] Exemplary Hot Zone Architecture Turning now to FIG. 2 , a first non-limiting exemplary embodiment of an improved SOFC system hot zone (2000) in accordance with the present technology includes a SOFC fuel cell stack (2005) including multiple individual fuel cells enclosed within a hot zone cavity (2010). The hot zone cavity (2010) is surrounded by an enclosure wall (2015), which is formed from one or more of copper, molybdenum, aluminum-copper, copper-nickel alloy, or combinations thereof. The enclosure wall is surrounded by an insulating layer (2012) that restricts thermal energy from exiting the hot zone. An air gap (2155) is disposed between the hot zone enclosure wall (2015) and the insulating layer (2012). The air gap (2155) provides a fluid flow conduit leading to a hot zone exit port (2165) and is used to convey exhaust gases from the hot zone.

[0034] The enclosure wall (2015) is configured to provide a thermal conduction path comprising a material having a thermal conductivity coefficient of 100-300 W / (m·K), preferably greater than 200 W / (m·K). Further, the thermal conduction path is positioned to function as a thermal energy conduit suitable for conducting thermal energy from a higher temperature region of the hot zone to a lower temperature region of the hot zone to narrow the temperature differential between the regions of the hot zone.

[0035] reformer The hot zone cavity (2010) in this non-limiting exemplary embodiment is a can-shaped, cylindrical volume bounded by hot zone enclosure walls (2015), including side walls (2002), a top wall (2004), and a bottom wall (2006). The hot zone (2000) operates most efficiently at temperatures above 350°C or above 500°C, depending on the SOFC reaction being used, and can operate at temperatures ranging from 350 to 1200°C. Thus, each of the hot zone elements of the present technology is configured to reliably operate at the highest temperatures expected of that element, e.g., 350°C for some zones, and up to 1200°C for those within the fuel reformer (e.g., adjacent to the catalytic reaction) or within the combustion region.

[0036] According to one preferred, non-limiting exemplary embodiment of the present technology, a fuel reformer (2020) that uses an exothermic reaction to reform a feed fuel-air mixture (2025) is provided within or partially within the hot zone to reform the feed fuel to produce a fuel (2027) or reformate for delivery to each of the fuel cells in the fuel cell stack (2005). In this exemplary embodiment, the reformer (2020) includes a catalytic partial oxidation (CPOX) reactor that partially combusts the feed fuel-air mixture (2025) delivered thereto. The feed fuel reforming process produces a hydrogen-rich fuel (2027), e.g., a reformate. The CPOX reactor includes a catalytic media (2040), such as a metal or oxide phase of rhodium (Rh) or other suitable catalyst (e.g., Pt, Pd, Cu, Ni, Ru, and Ce), coated on its inner surface. The feed fuel-air mixture (2025) passing through the CPOX reactor is catalyzed as it passes over surfaces coated with catalytic media (2040), and the heat released by the reaction is radiated and conducted to the hot zone enclosure walls (2015), helping to heat the fuel cell stack.

[0037] The CPOX reformer (2020) includes a reformer enclosure wall (2030) surrounding a cylindrical catalyst cavity (2035). The cylindrical catalyst cavity (2035) internally supports a catalytic media (2040). In this exemplary embodiment, the catalytic media (2040) is a square-cell extruded monolith with its exposed surfaces coated with a suitable catalyst. The monolith is positioned so that the incoming feed fuel-air mixture (2025) flows past the exposed surface of the square-cell extruded monolith for catalytic action. Other suitable catalytic structures may include multiple parallel plate or concentric ring structures, or porous metal or ceramic foam structures such as sintered or extruded elements formed with a catalytic agent coating on their exposed surfaces. Alternatively, the catalytic structure may include multiple mesh screens with their exposed surfaces coated with a catalytic agent. The feed fuel-air mixture (2025) enters the reformer (2020) through the reformer input port (2045) and flows through the catalytic media (2040) for reforming by contact with the catalytic surfaces. The reformed fuel or reformate, hereafter "fuel," exits the reformer through the reformer outlet port (2050) and flows into the fuel input manifold (2055).

[0038] In this non-limiting exemplary embodiment, the reformer enclosure wall (2030) includes a cylindrical or square wall surrounding a cylindrical or square cross-sectional catalyst cavity (2035). A catalyst media (2040) is supported inside the catalyst cavity (2035) arranged to force the incoming feed fuel-air mixture (2025) to flow past the catalyst surface and through the catalyst structure. A thermal insulation element (2065) is arranged to surround the outer surface of the catalyst cavity (2035). The thermal insulation element (2065) is provided to limit thermal energy entering or leaving the catalyst cavity (2035). The reformer enclosure wall (2030) may comprise a high-temperature steel alloy such as Inconel, a high-temperature copper alloy (e.g., Monel), or other suitable high-temperature material.

[0039] SOFC fuel cell stack The SOFC fuel cell stack (2005) is supported inside the can-shaped hot-zone enclosure wall (2015). A plurality of rod-shaped fuel cells (2080) are supported longitudinally inside the cathode chamber (2090). The cathode chamber (2090) is a cylindrical chamber bounded by the hot-zone enclosure side wall (2002) and a pair of opposing disk-shaped top and bottom tube support walls (2070 and 2075). Each tube support wall (2070, 2075) is attached to the side wall (2002) by suitable attachment means, such as by welding or brazing, by bracketing and mechanical fastening, or held in place without fasteners, such as by clamping force. Preferably, the fuel cell stack (2005) is assembled before installation in the hot-zone enclosure wall (2015) and is removable as a unit from the hot-zone enclosure wall (2015), for example, to repair or inspect the cell stack as needed. Thus, the top and bottom tube support walls (2070, 2075) can be captured in place between opposing end stops (not shown). The top tube support wall (2070) mechanically engages and fixedly supports the top or input end of each of the plurality of rod-shaped fuel cells (2080). The mechanical interface between the top support wall (2070) and each of the plurality of fuel cell input ends is substantially gas-tight to prevent the supply fuel-air mixture (2025) in the fuel input manifold (2055) from entering the cathode chamber (2090). The top tube support wall (2070) is preferably formed of Inconel. Each of the upper end caps (2095) is also formed of Inconel, which is an effective material for avoiding creep in high-temperature environments. The bottom tube support wall (2075) mechanically engages with and movably supports the bottom or output end of each of the plurality of rod-shaped fuel cells (2080). In particular, the output end of each fuel cell (2080) is longitudinally movable relative to the bottom tube support wall (2075) to accommodate changes in the length of each fuel cell as it is heated to an operating temperature between 350 and 1200°C.An example of a tube support system that can be used with the present technology is disclosed by Palumbo in related U.S. patent application Ser. No. 13 / 927,418, filed June 26, 2013, entitled "SOLID OXIDE FUEL CELL WITH FLEXIBLE ROD SUPPORT STRUCTURE."

[0040] 2 and 5C, the bottom tube support wall (2075) includes a disk-shaped thermally conductive mass (2180) comprising one or more materials (e.g., one or more of copper, molybdenum, aluminum copper, copper-nickel alloy, or combinations thereof) having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K). The disk-shaped thermally conductive mass (2180) is protected by a top protective surface layer (5045) and a bottom protective surface layer (5050), which are described below in connection with FIG. 5C. In one non-limiting exemplary embodiment, each top protective surface layer (5045) and bottom protective surface layer (5050) comprises a separate disk-shaped element in thermally conductive contact with the disk-shaped thermally conductive mass (2180). Specifically, the top surface layer (5045) facing the cathode chamber (2090) is made of a disk-shaped chromium-free high-temperature metal alloy such as Monel, and the bottom surface layer (5050) facing the combustion area (2135) or tail gas combustor is made of a disk-shaped high-temperature corrosion-resistant metal such as Hastelloy alloy.

[0041] Preferably, the top protective surface layer (5045) and the bottom protective surface layer (5050) are each in thermally conductive contact with a thermally conductive mass (2180), which is also in thermally conductive contact with the hot zone enclosure cylindrical side wall (2002). Thus, when the fuel-air mixture is combusted within the tail gas combustor or combustion region (2135), thermal energy generated by the combustion is radiated to the walls surrounding the combustion region (2135), conducted from the surrounding walls to the thermally conductive mass (2180), and through the hot zone enclosure wall (2015) to other regions of the hot zone. Thermal energy released from the thermally conductive mass (2180) is also radiated to the cathode chamber (2090), where it heats the cathode gas or air flowing therethrough and heats the surfaces of the fuel cells enclosed therein.

[0042] Each rod-shaped fuel cell (2080) includes a tubular annular wall (2085) with an anode layer as a support layer. The tubular annular wall (2085) is open at both ends. The tubular annular wall (2085) forms a fuel conduit that extends through the cathode chamber (2090) and carries the fuel (2027) therethrough. Other rod shapes, including square, triangular, pentagonal, hexagonal, etc., can be used without departing from the present technology. Other support layers can also be used to provide structural integrity. Each fuel cell includes two metal end caps (2095) and (2100) or a tube manifold adapter with one end cap attached to each of the two opposing ends of the tubular annular wall (2085).

[0043] Each end cap (2095) and (2100) or tube manifold adapter includes a cup-shaped mounting end (2105) and a journal-shaped support end (2110). The mounting end (2105) includes a blind bore sized to receive the outer diameter of the annular wall (2085). Each mounting end (2105) is fixedly attached to the rod end by a press fit or interference fit, or by another fastening means such as brazing or adhesive bonding using a material suitable for the hot zone operating temperatures (350-1200°C). The journal-shaped support end (2110) includes an annular wall formed with an outer diameter sized to engage corresponding through-holes through the input top tube support wall (2070) and the output bottom tube support wall (2075). The journal-shaped support end (2110) further includes a through-hole therethrough that serves as a cell input port (2115) at the top end of the rod-shaped fuel cell or a cell output port (2120) at the bottom end of the rod-shaped fuel cell (2080). Preferably, the end caps (2095 and 2100) or tube manifold adapters each comprise a high-temperature, low-Cr corrosion-resistant metal alloy that is thermally compatible with the fuel cell. The caps may be constructed with a ceramic coating on the metal cap to prevent Cr contamination.

[0044] 2 and 3, the top end cap (2095) of each fuel cell (2080) may provide electrical communication with the outer diameter of the annular wall (2085) or cathode layer, such that the outer diameter of the annular wall (2085) is in electrical communication with one of the DC current output terminals (140) on the electrical lead (2125) through the end cap (2095). A second electrical lead (2130) is in electrical communication with the inner diameter of the annular wall (2085) or anode layer and a different terminal of the DC current output terminal (140). Additionally, electrical insulators (not shown) are provided between each end cap (2095) and (2100) and the corresponding top and bottom tube support walls (2070 and 2075) to electrically insulate the hot zone enclosure wall (2015) from the electrical current being generated by the fuel cell stack (2005).

[0045] Each rod-shaped fuel cell is formed by an annular wall (2085) including an anode support layer, a structural anode material layer formed by an inner diameter and an outer diameter. The anode support layer may comprise a cermet, as previously described. The outer diameter of the anode support layer annular wall (2085) is at least partially coated with a ceramic electrolyte layer, such as yttria-stabilized zirconia or cerium (Ce) or lanthanum gallate-based ceramics. The outer diameter of the ceramic electrolyte layer is at least partially coated with a cathode material layer, such as lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), or lanthanum strontium manganite (LSM).

[0046] In a second non-limiting exemplary embodiment of the system hot zone (2000), the mechanical structure of the hot zone enclosure wall and interior end wall is similar to that shown in FIG. 2 and described above, except that the anode and cathode layers are on opposite sides of the ceramic electrolyte layer. Specifically, in this second embodiment, the inner diameter of the anode support layer annular wall (2085) (as opposed to the outer diameter) is at least partially coated with a ceramic electrolyte layer, such as yttria-stabilized zirconia or cerium (Ce) or a lanthanum gallate-based ceramic, and the inner diameter of the ceramic electrolyte layer is at least partially coated with a cathode material layer, such as lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt iron oxide (LSCF), or lanthanum strontium manganite (LSM). In this exemplary embodiment, the anode support layer of the annular wall (2085) is the outer diameter of each fuel cell, and the inner diameter of each fuel cell is the cathode layer. Thus, in the second exemplary embodiment, the cathode chamber (2090) becomes the anode chamber, and fuel is delivered to the anode chamber, while the cathode gas, air, flows through the rod-shaped fuel cell.

[0047] The fuel (2027) flows over the anode material layer while the cathode gas, an oxygen-containing gas (e.g., air), flows over the cathode material layer to generate a current flow. The current flow passes out of the cell stack via electrical leads (2125) and (2130) to DC current output terminals (140) and can be used to power an external device. Note that in other embodiments, such as the second embodiment briefly described above, the anode and cathode surfaces can be reversed without departing from the present technology, with a cathode layer on the inner diameter of the fuel cell and an anode layer on the outer diameter of the fuel cell, and air flowing through gas flow conduits formed by the fuel cell and fuel flowing on the outer surface of the fuel cell.

[0048] The fuel input manifold (2055) includes a cylindrical chamber bounded by a disk-shaped top wall (2170) and an opposing disk-shaped upper tube support wall (2070). The disk-shaped fuel input manifold top wall (2170) includes a thermally conductive mass (2160). The thermally conductive mass (2160) includes one or more materials having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K), such as one or more of copper, molybdenum, aluminum copper, copper-nickel alloy, or combinations thereof. The thermally conductive mass (2160) is in thermally conductive communication with the hot zone enclosure walls (2015), particularly the side walls (2002). The thermally conductive mass (2160) is positioned proximate to the annular cold start combustion chamber (2305) described below for receiving thermal energy from fuel combusted in the annular cold start combustion chamber (2305) during start-up and for conducting the received thermal energy to the hot zone outer wall (2015). The thermally conductive mass (2160) also radiates the thermal energy received from fuel combustion in the annular cold start combustion chamber (2305) and by conduction through the hot zone enclosure wall to the fuel (2027) as it passes through the fuel input manifold (2055).

[0049] The upper tube support wall (2070) forms an airtight seal with the journal-shaped support end (2110) of each fuel cell upper end cap (2095), and each fuel cell (2080) is fixedly suspended from the upper tube support wall (2070) by a mechanical interface formed in the upper tube support wall (2070) that includes through-holes for receiving the journal-shaped support end (2110) or manifold adapters therethrough. The fuel input manifold (2055) is bounded by a side wall (2002).

[0050] Because this exemplary embodiment utilizes a CPOX reformer (2002) that reforms the feed fuel using an exothermic reaction, the reformer (2020) is a thermal energy source advantageously located within the hot zone (2000) to heat the incoming feed fuel-air mixture (2025) as the fuel enters the hot zone. However, in other embodiments of the SOFC system of the present technology, the reformer (2020) may utilize an endothermic reaction (e.g., a steam reformer) or a thermally neutral reaction (e.g., an autothermal reformer for reforming the fuel). In these cases, the reformer (2020) may be located outside the hot zone (2000) and instead located in the cold zone (110) shown in FIG. 1. Thus, the modified hot zone (2000) of the present technology may operate without the reformer (2020) without departing from the present technology.

[0051] Tail Gas Combustor The tail gas combustor or combustion zone (2135) is an annular volume located between a disk-shaped bottom tube support wall (2075) containing a thermal mass (2180) (both described above and illustrated in FIG. 2) and a disk-shaped combustor end wall (2140) that also contains a thermal mass (2175). Both thermal masses (2180) and (2175) comprise one or more materials having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K), such as copper, molybdenum, aluminum copper, copper-nickel alloys, or combinations thereof. The thermal masses (2180) and (2175) are positioned to receive thermal energy from the combustion region (2135) and are configured to conduct the thermal energy received from the combustion region to the hot zone enclosure wall (2015) and to radiate the thermal energy received from the combustion region to the cathode chamber (2090) and the recuperator chamber (2210).

[0052] An annular combustor baffle (2185) is provided within the annular combustor region to redirect gas flow through the combustion region (2135) and create turbulence that increases convective energy transfer to the sidewalls of the combustion region (2135). The combustor baffle (2185) may be fixedly attached to the hot zone enclosure sidewall (2002) or may comprise part of a combustion chamber liner, as described below.

[0053] A cathode feed tube (2145), described below, passes through the combustion zone (2135) along a central longitudinal axis (2060). The walls of the cathode feed tube (2145) are heated by convective heat energy transfer from the combustion gases within the combustion zone (2135). Air flowing through the cathode feed tube (2145) toward the cathode chamber (2090) is heated by heat energy radiated from the cathode feed tube (2145) to the air flowing therethrough.

[0054] The inner wall of the combustion region (2135) is lined with a high-temperature, corrosion-resistant metal, such as Hastelloy alloy. In the case of the disk-shaped bottom tube support wall (2075), the surface facing the combustor region comprises Hastelloy. In the case of the combustor region end wall (2140), the surface facing the combustor region comprises Hastelloy. In both cases, the walls (2075) and (2140) are formed as a composite structure with a Hastelloy disk-shaped liner in thermally conductive contact with the corresponding thermal masses (2180) and (2175), respectively. The side wall of the combustion region (2135) is also lined with a high-temperature, corrosion-resistant metal, such as Hastelloy. In one non-limiting exemplary embodiment, the side wall liner comprises a separate element formed as a tubular, open-ended, cylindrical wall with a combustor baffle (2185) integrally formed therewith. Additionally, the sidewall liner is inserted into the hot zone enclosure sidewall (2002) from one of its open ends and is formed to be in thermally conductive contact with the sidewall (2002) over substantially the entire surface of the wall liner.

[0055] recuperator Air (2200) enters the cathode feed tube (2145) through an input port (2205) and flows into a recuperator chamber (2210). The recuperator chamber (2210) is located in close proximity to the tail gas combustion zone (2135) to heat the incoming air (2200) using thermal energy generated by the combustion of spent fuel occurring within the combustion zone (2135). The recuperator chamber (2210) is an annular chamber surrounding the cathode feed tube (2145) and is bounded at the top by the disk-shaped combustor end wall (2140), at the bottom by the disk-shaped hot zone enclosure bottom wall (2006), and laterally by the hot zone enclosure side walls (2002).

[0056] Thermal energy is conducted to the recuperator chamber (2210) walls by the hot-zone enclosure wall (2015), the combustor end wall (2140), and to a lesser extent, the cathode feed tube (2145). Thermal energy is radiated from the recuperator chamber walls to the air (2200) as it passes through the recuperator chamber (2210). The exterior walls of the recuperator chamber (2210) are further heated by the hot exhaust gases exiting the combustion zone (2135). Specifically, the recuperator chamber (2210) is surrounded by an air gap (2155) that carries the hot exhaust gases from the combustion zone (2135) through the combustor exit port (2150) and out the hot-zone exit port (2165). The thermal energy from the hot exhaust gases heats the exterior wall portions of the recuperator chamber walls by convective heat transfer.

[0057] The recuperator baffle (2215) is positioned inside the recuperator chamber (2210) and prevents air from passing through the cathode supply tube (2145). Thus, air (2200) entering the cathode supply tube (2145) through the input port (2205) strikes the recuperator baffle (2215) inside the cathode supply tube and is forced into the recuperator chamber (2210) through one or more air input ports (2225). The input air (2200) entering the recuperator chamber through the air input port (2225) passes around the recuperator baffle (2215) and is heated within the recuperator chamber (2210), before re-entering the cathode supply tube through one or more recuperator air output ports (2235).

[0058] Cold Start Combustor Referring to FIG. 2 , the SOFC hot zone (2000) optionally includes a cold start combustor (2300) provided to initially heat the hot zone to an operating temperature exceeding 350°C, or at least until autoignition occurs in the tail gas combustor region. The cold start combustor includes an annular start combustion chamber (2305). The annular start combustion chamber (2305) surrounds the catalyst cavity (2035) and the annular insulating element (2065). The annular start combustion chamber (2305) is bounded at the top by a disk-shaped hot zone enclosure upper wall (2004) and at the bottom by a disk-shaped fuel input manifold upper wall (2170), which contains an annular thermal mass (2175). The annular start combustion chamber (2305) is further bounded by the hot zone enclosure side wall (2002).

[0059] The starter combustor inlet port (2310) receives unreformed starter fuel (2315) therein from a starter fuel source (not shown). The starter fuel (2315) can include various combustible gaseous or vaporized liquid fuels, such as natural gas, propane, methane, hydrogen, alcohol, or a mixture of fuel and air. In some exemplary embodiments, the starter fuel (2315) includes a feed fuel-air mixture (2025). The starter fuel (2315), along with air or other oxygen-containing gas, is delivered through the combustor inlet port (2310) to the annular starter combustion chamber (2305) and ignited by an electric spark igniter (2320) or other ignition source.

[0060] During startup combustion, heat energy generated by startup fuel combustion inside the annular startup combustion chamber (2305) is transferred by convective heat energy transfer to the hot zone enclosure top wall (2004) and side walls (2002) and the fuel input manifold top wall (2170). From each of these walls, heat energy from the startup combustion is conducted to other areas of the hot zone by the thermally conductive hot zone enclosure walls (2015).

[0061] Exhaust gases from the startup combustion exit the annular startup combustion chamber (2305) through the startup combustor exit port (2325), which is in fluid communication with the air gap (2155) that leads to the hot zone exit port (2165). Thus, the exhaust gases flowing from the annular startup combustion chamber (2305) to the hot zone exit port (2165) further heat the exterior surface of the hot zone enclosure wall (2015) by convective heat transfer.

[0062] The inner wall of the annular startup combustion chamber (2305) is lined with a high-temperature, corrosion-resistant metal such as Hastelloy. In the case of the disk-shaped hot zone enclosure top wall (2004), this wall is lined on its inner surface with a layer of Hastelloy material, which is in thermally conductive contact with the hot zone enclosure top wall (2004). In the case of the disk-shaped fuel input manifold top wall (2170), the upper surface of this wall includes a layer of Hastelloy material in thermally conductive contact with the annular thermally conductive mass (2175). In the case of the side walls, a cylindrical wall liner including Hastelloy material is inserted into the startup combustion chamber in thermally conductive contact with the hot zone enclosure side wall (2002).

[0063] Gas Flow Diagram fuel flow diagram Referring now to FIG. 3, a schematic fuel flow diagram illustrates the flow path of the feed fuel-air mixture (2025) as it passes through the hot zone (2000). The feed fuel-air mixture (2025) enters the reformer input port (2045) and passes through the reformer catalyst cavity (2035) to produce fuel (2027), e.g., reformate (reformed fuel). The fuel (2027) exits the reformer through the reformer outlet port (2050) and enters the fuel input manifold (2055). From the input manifold (2055), the fuel enters each of the fuel cells (2080) through the corresponding cell input port (2115), flows through each fuel cell, and exits the fuel cell through the corresponding cell output port (2120). Inside the fuel cells (2080), the fuel reacts with the anode material layer that forms the inner surface of the cell annular wall (2085). After exiting the fuel cell through the cell exit port (2120), the remaining fuel (2027), including unreacted fuel and reaction by-products, enters the combustion region (2135), where it mixes with air exiting the cathode chamber (2090) to form a mixture that spontaneously combusts therein. As described above, thermal energy generated by combustion in the combustion region (2135) is transferred by radiation and convection to the side walls of the combustor region and then through the hot zone enclosure wall (2015) to other regions of the hot zone. Thermal energy generated by combustion in the combustion region (2135) can also be transferred to each of the thermally conductive masses (2175) and (2180) adjacent to the combustor region by gas-to-surface heat transfer via convection and thermal conduction through the enclosure wall. Additionally, the thermally conductive masses (2175) and (2180) adjacent the combustor region radiate thermal energy to the recuperator chamber (2210) and cathode chamber (2090), respectively, to heat the air passing therethrough.

[0064] After combustion, exhaust gases from the combustion mixture (shown as dashed arrows) exit the combustion zone (2135) through one or more combustor exit ports (2150) and reach the air gap (2155). From the air gap (2155), exhaust gases from the combustion mixture exit the hot zone through hot zone exit ports (2165).

[0065] Fuel flow diagram cold start As further shown in FIG. 3, start-up fuel (2315) and air enter the annular start-up combustion chamber (2305) through the start-up combustor inlet port (2310) where the start-up fuel is combusted.

[0066] After combustion, the exhaust gases (shown as dashed arrows) exit the combustion zone (2135) through one or more start-up combustor exit ports (2325) and reach the air gap (2155). From the air gap (2155), the exhaust gases from the start-up combustor exit the hot zone through the hot zone exit ports (2165).

[0067] Airflow Diagram Referring now to FIG. 4, a schematic airflow diagram illustrates the path of air (2200) as it passes through the hot zone (2000). Air (2200) enters the cathode supply tube (2145) through air input port (2205). Air (2200) exits the cathode supply tube through recuperator air input port (2230) and enters the recuperator chamber (2210). Air flows around the recuperator baffle (2215) and re-enters the cathode supply tube (2145) through the recuperator air output port (2235). Within the recuperator chamber (2210), the air (2200) is heated by thermal energy radiating from the recuperator chamber walls (2006), (2002), and the combustor end wall (2140) and associated annular thermally conductive mass (2175).

[0068] As the air (2200) flows through the cathode feed tube (2145), it passes through the combustion zone (2135). In the combustion zone, the air, while still flowing through the cathode feed tube (2145), is further heated by thermal energy radiating from the surface of the cathode feed tube (2145) before entering the cathode chamber (2090). The air (2200) exits the cathode feed tube and enters the cathode chamber (2090) through a plurality of cathode chamber air input ports (2240) located along a portion of the length of the cathode feed tube (2145) that extends into the cathode chamber (2090).

[0069] Upon entering the cathode chamber (2090), the air (2200) fills the cathode chamber, impinges on each outer diameter or cathode layer of the fuel cell (2080), and reacts on the cathode material layer coated on at least a portion of each outer diameter of the fuel cell. The reaction between the air passing over the cathode material layer and the fuel (2027) passing over the anode material layer forming each inner diameter of the fuel cell produces a flow of electrical current that is carried to the DC current output terminals (140) on electrical leads (2125) and (2130) shown in FIG. 3.

[0070] After reacting with the cathode material layer coated on each of the fuel cells, the oxygen-reduced air (2200) (illustrated as a dashed flow line) exits the cathode chamber (2090) through one or more cathode chamber output ports (2245) that lead to the combustion zone (2135). In the combustion zone (2135), the oxygen-depleted air mixes with unconsumed fuel (2027) exiting the fuel cells, and the mixture is combusted. Exhaust gases from the combustion mixture exit the combustion zone (2135) through combustor exit ports (2150) that lead to an air gap (2155). The air gap (2155) carries the exhaust gases to the hot zone exit ports (2165) and out of the hot zone.

[0071] While Figure 4 schematically illustrates a pair of two diametrically opposed recuperator air input ports (2230), two diametrically opposed recuperator air output ports (2235), and two diametrically opposed cathode chamber air input ports (2240), an actual device may include any hole pattern with one or more holes arranged around the circumference of the cathode supply tube (2145) as needed for airflow distribution. Similarly, while Figure 4 illustrates two diametrically opposed cathode chamber air output ports (2245) and two diametrically opposed combustor exit ports (2150), an actual device may include any hole pattern with one or more holes arranged around the circumference of the disk-shaped wall (2004) or side wall (2002) as needed for airflow distribution. Alternatively, any of the above gas ports may be non-circular in shape, such as square, rectangular, and oval, or slotted, without departing from the present technology.

[0072] Enclosure wall treatment According to one aspect of the present technology, copper surfaces are not exposed to oxygen / air to avoid oxidation damage to the copper. This includes all surfaces forming the entire fuel flow path and all surfaces forming the entire air flow path, since both fuel and air contain or may contain oxygen. Copper surfaces that may be exposed to the fuel or air flow are protected by at least a layer of nickel plating applied, such as by electroplating, to a thickness of 0.0005 to 0.0015 inches (12.5 to 38.1 μm). The nickel plating thickness is more than 100 times the typical thickness of conventional nickel electroplating, and the thicker nickel coating is used to substantially prevent oxygen diffusion through the nickel coating.

[0073] This aspect of the present technology is illustrated in FIG. 5A, which shows a non-limiting exemplary cross-section through one of the hot zone enclosure walls (2015). The hot zone cavity wall section (5005) includes a copper core (5010) comprising copper having a thermal conductivity in the range of approximately 370 W / (m·K) at 500°C and 332 W / (m·K) at 1027°C. The thickness of the copper core (5010) ranges from 0.01 to 0.125 inches (0.25 to 3.2 mm), although other thicknesses can be used without departing from the present technology. More generally, the thickness of the hot zone cavity wall can be increased or decreased as needed for a particular application. Thicker enclosure walls (e.g., up to about 0.25 inches) generally take longer to heat up to the desired operating temperature, but once heated to operating temperature, thicker walls have a greater heat conduction capacity, are less likely to form thermal gradients, and offer the advantage of a longer operating life than thinner walls if surface oxidation is the failure mode, simply because it takes longer for thick walls to oxidize to the point where they become unusable.

[0074] The copper core (5010) includes two opposing surfaces that form the inner and outer surfaces of the enclosure wall. In a preferred embodiment, the inner and outer surfaces of the copper core (5010) are completely covered by electrodeposited nickel coating layers (5015) and (5020) on the inner and outer surfaces, respectively. Each nickel coating layer is applied to a layer thickness of at least 0.0005 inches (12.5 μm), which is adequate to prevent oxygen diffusion through the nickel coating layer. More typically, a desired nickel coating layer thickness in the range of 0.0005 to 0.0015 inches (12.5 to 38.1 μm) provides adequate surface protection from oxidation for a product life of up to about 40,000 hours, although thicker nickel coatings can be used to increase product life without departing from the present technology. Referring to FIG. 2, wall section (5005) represents at least the outer walls of the hot zone enclosure wall (2015), including the side wall (2002), the disk-shaped top wall (2004), and the disk-shaped bottom wall (2006), and may represent some walls of the reformer enclosure wall (2030).

[0075] According to one aspect of the present technology, the combustion chamber surface is lined with a high-temperature corrosion-resistant metal, such as Hastelloy alloy, to protect the interior surface of the combustion chamber from surface damage due to exposure to hot combustion by-products and corrosive elements. Alternatively, Monel or Inconel can be used without departing from the present technology.

[0076] This aspect of the present technology is illustrated in FIG. 5B, which shows a non-limiting, exemplary cross-sectional view (5025) through a combustion chamber sidewall. The sidewall section (5025) includes the copper core (5010) of the hot-zone enclosure sidewall (2002) and the electroplated nickel coating layers (5015) and (5020) applied to opposite sides of the copper core, as described above. Specifically, the cross-sectional view (5025) includes the same hot-zone outer wall (5005) as shown in FIG. 5A. The combustion chamber sidewall section (5025) also includes a Hastelloy alloy liner (5030) positioned to line the interior surface of the combustion chamber. Referring to FIG. 2, the sidewall section (5025) represents at least the cylindrical outer wall of the annular tail gas combustion region (2135) and the cylindrical outer wall of the annular cold start combustion chamber (2305). The sidewall section (5025) represents the hot zone sidewall (2002) protected by the Hastelloy alloy liner element (5030). In the particular example of the tail gas combustion region (2135), the Hastelloy alloy liner element (5030) also includes a combustor baffle (2185) attached thereto or integrally formed therewith. However, apart from the presence of the combustor baffle (2185), the section (5025) also represents the top and sidewalls of the annular cold start combustion chamber (2305).

[0077] The combustion regions (2135) and (2305) are also each lined by a pair of opposing disc-shaped Hastelloy alloy liner elements arranged to line the inner top and bottom surfaces of the combustor region. In the case of the tail gas combustor region (2135), its chamber top wall is formed by a bottom tube support wall (2075) including a disc-shaped Hastelloy alloy liner element (5050), as shown in FIG. 5C. The liner element (5050) is arranged to face the interior of the annular tail gas combustion region or chamber (2135). The bottom wall of the tail gas combustion region is formed by a combustor end wall (2140) that also includes a disc-shaped Hastelloy alloy liner (5060) facing the interior of the annular combustion region chamber (2135).

[0078] In the case of the annular cold start combustion chamber (2305) of the cold start combustor (2300), its upper chamber wall is formed by a hot zone enclosure upper wall (2004) that includes an annular-shaped Hastelloy alloy liner element (5030) that contacts the inner upper wall of the annular cold start combustion chamber (2305). Specifically, the hot zone enclosure upper wall (2004) and the upper wall of the annular cold start combustion chamber (2305) are detailed in cross section in Figure 5B, which shows a copper core (5010) coated on its inner surface with an electrodeposited nickel layer (5015) and on its outer surface with an electrodeposited nickel layer (5020), including a Hastelloy alloy liner element (5030) that contacts the nickel layer (5015). The cross section (5025) is vertical and includes a Hastelloy combustor baffle (2185), but the cross section is the same as the top wall (2004) except for the combustor baffle (2185), which is rotated horizontally like the top wall (2004).

[0079] The bottom wall of the annular cold start combustion chamber (2305) is formed by the top wall of the fuel input manifold (2170), which also includes an annular shaped Hastelloy alloy liner element (5060) that is in mating contact with the inner bottom wall of the annular cold start combustion chamber (2305), similar to that shown in FIG.

[0080] According to one aspect of the present technology, in order to avoid contamination of the cathode layer applied to the exterior surface of the fuel cell (2080), the incoming air (2200) is not exposed to surfaces formed from materials containing chromium. This includes all surfaces forming the entire incoming air flow path, including the interior surface of the cathode supply tube (2145), the recuperator chamber (2210), the recuperator baffle (2215), the exterior surface of the cathode supply tube (2145), the interior surface of the cathode chamber (2090), and elements contained within the cathode chamber, including the fuel cell end caps (2095) and (2100) and the top and bottom tube support walls (2070 and 2075).

[0081] In one non-limiting exemplary embodiment, the cathode supply tube (2145), recuperator baffle (2215), and bottom end cap (2100) are each formed from a chromium-free, corrosion-resistant, high-temperature metal alloy (e.g., Monel alloy). Additionally, at least the bottom surface of the combustor end wall (2140), which forms the upper surface of the recuperator chamber (2210), is formed from or lined with a protective element formed from a chromium-free, corrosion-resistant, high-temperature metal alloy (e.g., Monel alloy). Similarly, at least the top surface of the bottom tube support wall (2075), which forms the bottom surface of the cathode chamber (2090), is formed from or lined with a protective element formed from a chromium-free, corrosion-resistant, high-temperature metal alloy (e.g., Monel alloy).

[0082] The interior surfaces associated with the incoming airflow, coated with the electroplated nickel layer, may be exposed to the airflow without exposure to chromium. Nickel-plated surfaces that may come into contact with the incoming airflow include the sidewalls (2002) forming the recuperator chamber (2210) and the cathode chamber (2090), and the disk-shaped bottom wall (2006) forming the bottom wall of the recuperator chamber (2210). These surfaces each have the cross-section (5005) shown in FIG. 5A. Other surfaces within the cathode chamber (2090) formed from chromium-containing materials, such as the upper tube support wall (2070) and upper end cap (2095), each made of Inconel, are covered with a nickel layer applied, such as by electroplating, to a thickness of 0.0005 to 0.0015 inches (12.5 to 38.1 μm) to prevent airborne contamination by chromium.

[0083] Referring now to FIG. 5C, a detailed cross-sectional view shows a cross section (5040) through the bottom tube support wall (2075). The detailed cross-sectional view shows a thermally conductive mass (2180) comprising a mass of copper having a thermal conductivity ranging from approximately 370 W / (m·K) at 500°C to 332 W / (m·K) at 1027°C. The thickness of the copper mass (2180) ranges from 0.01 to 0.375 inches (2.5 to 9.5 mm), although other thicknesses can be used without departing from the present technology. The top surface of the bottom tube support wall (2075) faces the inside of the cathode chamber (2090) and is therefore lined with a disk-shaped liner element (5045) formed from a chromium-free, corrosion-resistant high-temperature metal alloy (e.g., Monel alloy) to prevent chromium contamination of the cathode gas. The bottom surface of the bottom tube support wall (2075) faces the tail gas combustion region (2135) and is lined with a disk-shaped liner (5050) made of Hastelloy alloy.

[0084] Referring now to FIG. 5D, a non-limiting exemplary detailed cross-section shows a cross section (5055) through a combustor end wall (2140). The detailed cross-section shows the thermally conductive mass (2140) comprising a mass of copper having a thermal conductivity ranging from approximately 370 W / (m·K) at 500°C to 332 W / (m·K) at 1027°C. The thickness of the copper mass (2175) ranges from 0.01 to 0.375 inches (2.5 to 9.5 mm), although other thicknesses can be used without departing from the present technology. The upper surface of the wall (2140) faces the interior of the tail gas combustion region (2135) and is therefore lined with an annular liner element (5060) formed from solid Hastelloy alloy. The bottom surface of the wall (2140) faces the recuperator chamber (2210) and is lined with an annular liner (5065) made of a chromium-free, corrosion-resistant high-temperature metal alloy (e.g., Monel alloy).

[0085] Referring now to FIG. 5E, a non-limiting exemplary cross-sectional view (5070) shows a cross section through the fuel input manifold top wall (2170). The cross-sectional view shows a thermally conductive mass (2160) comprising a mass of copper having a thermal conductivity ranging from approximately 370 W / (m·K) at 500°C to 332 W / (m·K) at 1027°C. The thermally conductive copper mass (2160) has a thickness ranging from 0.01 to 0.375 inches (2.5 to 9.5 mm), although other thicknesses can be used without departing from the present technology. Opposite top and bottom surfaces of the thermally conductive copper mass (2160) are optionally covered with a nickel plating layer (5075) applied, such as by electroplating, to a thickness of 0.0005 to 0.0015 inches (12.5 to 38.1 μm). The nickel plating is applied to avoid contact between the supply fuel-air mixture (2025) and the thermally conductive copper mass (2160) and to prevent oxidation of the copper mass surface. The upper surface of the fuel input manifold upper wall (2170) faces the inside of the annular cold start combustion chamber (2305) and is therefore lined with an annular liner element (5080) formed from solid Hastelloy alloy to protect the thermally conductive mass (2160) from thermal damage.

[0086] A further variation of the walls (2075) and (2180), shown in detail in Figures 5D and 5C, is that both sides of the copper masses (2180) and (2175) are covered with a nickel-plated layer, applied to a thickness of 0.0005 to 0.0015 inches (12.5 to 38.1 μm), for example, by electroplating as described above with respect to Figure 5E. The nickel plating is included to prevent contact between the supplied fuel-air mixture (2025) and / or air (2200) and the corresponding copper masses (2180) and (2175) and to prevent oxidation of the copper mass surfaces. If the Hastelloy elements (5050) and (5060) and the Monel elements (5045) and (5065) comprise separate liner elements, i.e., not integrally formed with the copper mass (2180), the copper mass is preferably nickel-plated on both of its opposing surfaces (e.g., as shown in Figure 5E). However, in other cases where the disc-shaped or annular liner elements (5045), (5050), (5060), (5065) are integrally formed with the copper mass (2180) and / or (2175), nickel plating of the copper mass may not be required.

[0087] Typically, the Hastelloy and Monel elements described above are used to protect various surfaces from damage or to avoid contamination of the incoming air due to contact with chromium-containing surfaces, such as Inconel or Hastelloy surfaces. In one non-limiting exemplary embodiment, one or more protective elements are fabricated separately from the hot zone enclosure wall (2015) and installed in place during assembly, such as by brazing a protective material layer to the surface being protected. In the example of the copper mass (2180, 2175) shown in Figures 5C and 5D, the protective Monel and Hastelloy layers are brazed directly to opposing surfaces of the copper mass without nickel plating the copper mass. Preferably, the brazing step substantially gas-seals the copper mass, preventing air or fuel from contacting and oxidizing the surface of the copper mass.

[0088] In the example of the thermally conductive copper mass (2160) shown in FIG. 5E, a protective Hastelloy layer is brazed directly to the nickel layer (5075) on one surface of the copper mass located inside the combustion zone (2135). In this non-limiting exemplary embodiment, the Hastelloy layer is installed to protect the copper mass surface from direct exposure to combustion and corrosive elements. On the opposite surface, only the nickel layer is applied to the copper mass surface located inside the recuperator chamber (2210), as the nickel layer only needs to protect the copper mass surface from oxidation by the incoming air. In the example of FIG. 5E, because the copper surface is already protected by the nickel layer (5075) located between the thermally conductive copper mass (2160) and the Hastelloy layer (5080), the Hastelloy layer (5080) can be mechanically attached, for example, by fasteners or clamping in place, without the need to gas-seal the copper surface.

[0089] Thus, as noted above, particularly with respect to Figures 5B, 5C, 5D, and 5E, the Hastelloy and Monel elements can comprise multiple separate elements, such as disc-shaped elements (5040), (5050), (5060), (5065), and (5080), that are in mating contact with disc-shaped thermal mass elements (2180), (2175), and (2160), or the Hastelloy and Monel elements can comprise a cylindrical wall portion (e.g., (5030)) that is positioned in mating contact with an interior cylindrical wall surface of a combustion chamber, such as the side wall (2002) of the hot zone enclosure wall. The cylindrical wall portion is inserted into an appropriate location within the hot zone enclosure wall (e.g., within the annular cold start combustion chamber (2305) and within the tail gas combustion region (2135)) and brazed, welded, or otherwise fastened or clamped into place in mating contact with the surface being protected. In some embodiments, the Hastelloy and Monel elements can be applied directly to the conductive core surface (e.g., brazed directly to the surface of the thermally conductive mass) with a substantially gas-tight seal. In other embodiments, the thermally conductive mass or core wall surface is nickel-plated, and the Hastelloy or Monel elements can be applied over the nickel plating without the need to provide a substantial gas seal, and instead of brazing the entire surface to provide a gas seal, the elements can be held in place by clamps, mechanical fasteners, or brazing or spot welding at selected points. In further embodiments, any of the above structured walls can be formed as a metal casting with various layers of protective material formed on selected surfaces of the metal casting by well-known methods, including plating, sputtering, spray coating, hot dipping, etc.

[0090] However, in other non-limiting embodiments of the present technology, the outer and / or inner wall portions of the hot zone enclosure wall (2015) are formed from pre-fabricated multi-layer composite materials, including metal materials such as plates and / or tubing fabricated with multiple dissimilar metal layers that can be used to form the various hot zone enclosure walls described herein.

[0091] In a first step, sheets of dissimilar metals are bonded together by an extrusion or rolling process commonly referred to as cladding. In one exemplary embodiment, referring to FIG. 5C , a composite sheet including a copper ingot (2180), a Hastelloy alloy layer (5050), and a Monel alloy layer (5045) is roll-welded to form a composite sheet. Once formed, a bottom tube support wall (2075) is cut from the composite sheet, and holes and other features may be added in a secondary operation. The bottom tube support wall (2075) is then assembled to the hot zone enclosure wall (2015) by brazing, welding, mechanical fastening, clamping, high-temperature adhesive bonding, or the like. Also shown in FIG. 5D is a wall (2140) that includes the same material layers as the bottom tube support wall (2075) shown in FIG. 5C, but in reverse order, and may be cut from the same composite sheet, with holes and other features added in a secondary operation. The wall (2140) and bottom tube support wall (2075) are then each assembled to the hot zone enclosure wall (2015) by brazing, welding, mechanical fastening, clamping, high temperature adhesive bonding, or the like.

[0092] In one exemplary embodiment, referring to FIG. 5E, a composite sheet including a thermally conductive copper mass (2160) and a Hastelloy alloy layer (5080) is roll-welded to form a composite sheet. In this exemplary embodiment, the nickel layer (5075) may be omitted so that the composite sheet has only two layers. Once formed, the fuel input manifold top wall (2170) can be cut from the composite sheet, and holes and other features added in a secondary operation. The fuel input manifold top wall (2170) is then assembled to the hot zone enclosure wall (2015) by brazing, welding, mechanical fastening, clamping, high-temperature adhesive bonding, or the like. In a further step, the composite sheet can be nickel-plated on at least the copper surface to prevent oxidation of the exposed copper surface.

[0093] Referring also to FIG. 5B, a two-layer composite sheet including a copper core (5010) and a Hastelloy layer (5030) is roll-welded to form the composite sheet. In this exemplary embodiment, nickel layers (5015) and (5020) may be omitted so that the composite sheet has only two layers. Once formed, holes and other features are formed in a secondary operation, and the composite sheet is then formed into a cylindrical wall. The cylindrical wall is cut to size and assembled with other cylindrical wall sections to form portions of the hot zone enclosure side wall (2002) associated with enclosing the combustion region. The cylindrical wall sections can be joined together by brazing, welding, mechanical fastening, clamping, high-temperature adhesive bonding, etc. In a further step, the composite sheet can be nickel-plated on one or both sides, and the side walls of the assembled host zone enclosure can be nickel-plated to protect the exposed copper surfaces from oxidation.

[0094] SOFC fuel cell stack configuration Referring now to Figure 6, a portion of a non-limiting exemplary embodiment of an SOFC system embodiment (7000) usable with the present technology is shown in horizontal cross section. The configuration (7000) shows a cathode chamber (7010) surrounded by a circular hot zone enclosure wall (7015), shown in horizontal cross section. The circular enclosure wall (7015) is surrounded by a circular insulation layer (7020) separated from the circular enclosure wall by a small air gap (not shown), which can be used as a gas flow conduit as described above.

[0095] The cathode supply tube (7025) is centered relative to the circular hot zone enclosure wall (7015). A plurality of rod-shaped fuel cells are arranged in two concentric circular patterns, each centered relative to the same central axis (7030). The inner circular pattern (7035) contains eight inner rod-shaped fuel cells (7040). The outer circular pattern (7045) contains fourteen outer rod-shaped fuel cells (7050). Other enclosure shapes and fuel cell patterns may be used without departing from this technology.

[0096] Alternative SOFC System Embodiments Turning now to Figures 7-9 and 12-15, a first alternative, non-limiting exemplary embodiment of a portion of an improved SOFC system (8000) shown in Figures 7A-9C includes a U-shaped primary enclosure wall assembly (8045) surrounding an SOFC stack (8005). A second alternative, non-limiting exemplary embodiment of a portion of an improved SOFC system is shown in Figures 12-13B. The second alternative SOFC system includes two L-shaped primary enclosure wall assemblies (12045), each L-shaped primary enclosure wall assembly (12045) surrounding a single SOFC stack (8005), providing a dual-stack SOFC system (12000). A third alternative, non-limiting exemplary embodiment of a portion of an improved SOFC system (14000) is shown in Figure 14. A third alternative SOFC system (14000) includes one L-shaped primary enclosure wall assembly (12045) surrounding a single SOFC stack (8005). A fourth alternative, non-limiting embodiment of a portion of an improved SOFC system (15000) is shown in FIG. 15. The fourth alternative SOFC system (15000) includes two U-shaped primary enclosure wall assemblies (8045), each surrounding a different SOFC stack (8005). Each SOFC stack (8005) includes multiple individual fuel cells (8010). In a non-limiting exemplary embodiment, the individual fuel cells (8010) are arranged in pairs of two individual fuel cells arranged side-by-side along the stack lateral width axis (y), as defined by a system coordinate axis diagram (8100) (shown in FIGS. 9A, 12, and 14). In this embodiment, multiple pairs of two fuel cells (8010) are arranged side-by-side along the longitudinal length axis (x) of the stack. However, the technology described herein is not limited to the exemplary arrangement of fuel cells in this embodiment, nor is it limited to tubular fuel cells. Other suitable arrangements of fuel cells in the SOFC stack can be used without departing from the concepts of the technology described herein. The number of fuel cells (8010) in the SOFC stack is selected to meet predefined power generation demands or other stack capacity considerations.In other embodiments, the number of fuel cells arranged along either the stack lateral width axis (y) or the stack longitudinal length axis (x) can be one or more, with the total number of individual fuel cells (8010) selected to meet predefined power generation demands or other stack capacity considerations.

[0097] In one non-limiting exemplary embodiment, each fuel cell (8010) includes an open-ended hollow fluid conduit disposed along the central axis of the conduit. The hollow fluid conduit is preferably cylindrical or elliptical in shape, although other fluid conduit shapes, such as square, rectangular, triangular, or other polygonal shapes, can be used without departing from the present technology. Alternatively, the hollow fluid conduit can be arranged in any embodiment that includes an anode layer separated from a cathode layer by an electrolyte layer, with anode gas (e.g., reformate or syngas) passing over the anode layer and cathode gas (e.g., air) passing over the cathode layer, without departing from the present technology.

[0098] Each fuel cell is formed by a peripheral wall surrounding a hollow fluid conduit. The peripheral wall is composed of three main material layers, each of which is shown schematically in FIG. 1 . The three main material layers include an anode layer or fuel electrode (150), a cathode layer or air electrode (155), and an electrolyte layer (145) separating the anode layer from the cathode layer. All layers include solid materials, some of which (e.g., the anode) may include solid materials formed in a porous structure. In this non-limiting exemplary embodiment, the peripheral wall includes an inner surface formed by an anode layer, an outer surface formed by a cathode layer, and an electrolyte layer disposed between the anode and cathode layers. Preferably, one of the three layers, e.g., the anode layer, is configured as a support layer, and the support layer is formed with sufficient structural rigidity and integrity to support each individual fuel cell (8010) in the operating position described below.

[0099] 7A and 7B, each fuel cell (8010) includes a fuel input end (8020) and a fuel output end (8025) corresponding to opposite open ends of the hollow fluid conduit. At least the fuel input end (8020) is supported by an interface with a fuel input manifold (8015) or other support structure. In one non-limiting example, the fuel input end (8020) of each fuel cell includes an end cap (2100) formed as a cup-shaped mounting end (2105) and a journal-shaped support end (2110) configured to mechanically interface the fuel input end of each fuel cell with the fuel input manifold (8015) such that the end cap (2100) couples the fuel input end to the fuel input manifold. Other mechanical interfaces of each fuel cell with the fuel input manifold (8015) can be used without departing from the present technology. The mechanical interface between each fuel cell (8010) and the fuel input manifold (8015) is configured to fixedly support each individual fuel cell (8010) in an operating position, with the central longitudinal axis of the hollow fluid conduit of each individual fuel cell (8010) supported substantially parallel to the stack gas flow axis (z). The mechanical interface between the fuel input manifold and the fuel input end (8020) of each individual fuel cell (8010) forms an airtight seal. In a preferred embodiment, the fuel output end (8025) of the fuel cell (8010) is unsupported, although an upper support structure or other mechanical support structure could be used to support the fuel output end (8025) of the individual fuel cell (8010) against the primary enclosure wall without departing from the present technology.

[0100] Compared to the embodiment shown in FIG. 2 and described above, in which the fuel (2027) flow is delivered to the top of the SOFC system and the cathode air (2200) flow is delivered to the bottom of the SOFC system (2000), the direction of fuel flow through the SOFC stacks shown in FIGS. 7A, 7B, 12, 14, and 15 is reversed because the corresponding fuel input manifold (8015) is located near the base or bottom end of the corresponding SOFC system, with only the bottom or fuel input end (8020) supported by the fuel input manifold (8015) and end cap (2100) or other connecting element. Thus, according to one aspect of the present technology, the fuel output end (8025) of an individual fuel cell is unsupported or mechanically interfaced with other elements of the SOFC system. This support structure is advantageous because it allows the fuel cell to expand and contract longitudinally during thermal cycling (e.g., on-off cycling), thereby avoiding stress on the fuel cell during thermal cycling. This support structure is also advantageous because it does not require a gas seal at the fuel output end (8025). Overall, the lack of an output end support reduces cost and complexity while improving reliability by eliminating a potential system failure mode.

[0101] As shown in each of Figures 7A, 7B, 12, 14, and 15, the fuel output end (8025) of each individual fuel cell (8010) is positioned so that the fuel passes through the hollow conduits, interacts with the anode layer forming the inner surface of each hollow conduit, and then discharges spent fuel from the fuel output end (8025) to a combustion zone (8030). As shown by the dashed fuel flow indicator lines and arrows in Figures 7A, 7B, 12, 14, and 15, a supply of fuel exits the fuel reactor or fuel reformer (8035) and flows through a fuel delivery conduit (8040) to a fuel input manifold (8015), where the fuel flow is distributed from the fuel input manifold to the fuel input ends (8020) of each individual fuel cell (8010).

[0102] The fuel reformer (8035) is described above as the fuel reformer (2020) shown in FIG. 2 and the fuel reformer (165) shown in FIG. 1. Details of non-limiting embodiments of the fuel reformer (8035) are disclosed in related U.S. patent application Ser. No. 15 / 287,402, filed October 16, 2016, and published February 25, 2020, as U.S. Patent No. 10,573,911 B2. As the fuel passes through each fuel cell, oxygen ions (O ) are transferred from the cathode layer to the anode layer. + ) to deplete hydrogen (H) and carbon monoxide (MO) to produce a flow of electrical current. The depleted or spent fuel exits each fuel cell through an output end (8025) and mixes with spent cathode air in a combustion region (8030). Other fuel reformer configurations and modes of operation can be used without departing from this technology.

[0103] The SOFC system (2000) shown in Figures 2-4 and described above includes individual fuel cell input ports or input ends (2125) located at the top of the SOFC stack and a fuel cell output port or output end (2120) located at the bottom of the SOFC stack. The SOFC system (2000) also includes a fuel input manifold (2055) located above the fuel cell input ports or input ends (2125). The SOFC system (2000) also includes an annular cold start combustion chamber (2305) surrounding the catalyst cavity (2035) of the fuel reformer (2035). The SOFC system (2000) also includes a tail gas chamber (2135) and a recuperator chamber (2210) located at the bottom of the SOFC stack to receive spent fuel from the fuel cell output port or output end (2120). The SOFC system (2000) receives inlet air (cathode gas) into the recuperator chamber (2210) through an air input port (2225) located at the bottom end of the SOFC system (2000) and discharges exhaust gas from the recuperator chamber through a hot zone outlet port (2165). As further shown in Figure 2, the feed fuel-air mixture (2025) enters the SOFC system (2000) and flows to the fuel reformer (2020) for steady-state operation and then through an inlet port (2310) into the start-up combustion chamber (2305), both of which are located at the top end of the SOFC stack.

[0104] In accordance with one aspect of the present technology, the alternative SOFC systems (8000, 12000, 14000, 15000) described herein provide alternative gas flow patterns compared to the gas flow characteristics of the system (2000) described above. Referring to Figures 7A, 9A, 12, 14, and 15, a feed fuel-air mixture (2025) is received in a corresponding fuel reformer (8035) at the top of the SOFC system. From the fuel reformer (8035), fuel (8150) is delivered to a corresponding fuel input manifold (8015) by a fuel delivery conduit (8040). In a preferred embodiment, the fuel delivery conduit (8040) is housed within an intermediate enclosure (9000) or an outer enclosure (16000), each of which is described below.

[0105] As best shown in FIG. 9A , start-up fuel (8152) is delivered to combustor assemblies (8155) through conduits (8145). The combustor assemblies extend through corresponding combustion zones (8030) and inject the start-up fuel (8152) into the combustion zones during cold start operation. Ignition devices (8160) are disposed within the combustion zones to ignite the fuel flow exiting the combustor assemblies to initiate combustion within the corresponding combustion zones (8030). As shown in FIGS. 12 and 15 , when the SOFC systems are duel stack systems, these systems preferably include a combustor assembly (8155) and an ignition device (8160) disposed within each combustion zone (8030). As described in more detail below, each combustor assembly includes a start-up fuel conduit (8145) for receiving start-up fuel (8152) from a connection with the supply fuel input line (160) or from a separate start-up fuel source. Each fuel delivery conduit (8040) may include one conduit segment connected to one or more start-up conduits (8145) for use during start-up. The corresponding fuel delivery conduit may include control elements, such as valves and valve actuator elements operable by the electronic controller (190), to independently regulate fuel flow under control of the electronic controller (190) and / or to divert fuel from the fuel reformer (8035) to one or more fuel input manifolds (8015) to divert supply fuel from the supply fuel input line (160) to one or more start-up conduits (8145).

[0106] Alternative SOFC cold start operation 7A, 9A, 12, 14, and 15, cathode air is admitted via cathode input port (9040) into a corresponding recuperator chamber (9050) at the top of the SOFC system, and exhaust gases are directed through exhaust ports (9045) also located at the top of the SOFC system and out through hot zone exhaust conduit (9055). Thus, as best shown in FIG. 16B, each of the alternative SOFC systems (8000, 12000, 14000, 15000) of the present technology are configured with all input and outlet gas ports extending from the top wall of the SOFC system.

[0107] The combustion region (8030) includes a combustor element (8155) shown in FIG. 9A through which start-up fuel is delivered via a start-up fuel input conduit (8145) during cold start operation. The start-up fuel is ignited in the combustion region (8030), for example, by an electrical igniter (8160), to provide thermal energy for heating one or more primary enclosure wall assemblies (e.g., (8045) or (12045)) during cold start operation. After the SOFC system is heated to an operating temperature capable of supporting the SOFC reaction in the fuel cell, fuel flow is initiated from the fuel reformer (8035) to the SOFC stack via the input manifold (8015) to initiate the SOFC reaction. The start-up fuel can be, for example, a reformate produced by a fuel reformer, where fuel (8150) is supplied to the start-up conduit (8145) as start-up fuel (8052), the supply fuel-air mixture (2025), or an alternative start-up fuel (8152), such as propane. The start-up fuel can be delivered from another source, for example, via an additional start-up fuel conduit (16020) shown in FIG. 16A. In this embodiment, the start-up input conduit (16020) is fluidly interfaced with one or more start-up conduits (8145). An advantage of the configuration of the combustion region (8030) shown in Figures 7A, 7B, 12, 14, and 15 is that the combustion region (8030) is configured for two modes of operation: a start-up mode in which fuel is delivered to the combustor elements (8155), and / or a steady-state power generation mode in which fuel (8150) is delivered from the fuel input manifold (8015) to individual fuel cells and spent fuel and spent cathode gases are combusted within the combustion region (8030). In other embodiments and modes of operation, the fuel delivery conduits (8040) feed each of the start-up conduits (8145), and the start-up mode involves simultaneous delivery of fuel (8150) to the corresponding start-up combustor elements (8155) and fuel input manifold (8015).The functional combination of the combustion region (8030) for start-up and power generation is advantageous because it reduces the overall volume, parts count, and complexity of the SOFC system, and directly heats the fuel cell (8010), whose interior surface is heated by the primary enclosure wall assemblies (8045) and (12045), inflowing cathode air, and fuel flowing through the interior surface, and whose exterior surface is heated by the cathode airflow and by thermal energy radiated and convectively transferred from the primary enclosure wall assemblies, as described below. Compared to the embodiment shown in Figures 1-4, the start-up chamber (2035) more directly heats the fuel reformer, and the inflowing anode gas configuration, which includes the combustion region (8030) surrounded by the combustion wall section, more directly heats the primary enclosure wall assemblies (8045, 12045), which redistribute thermal energy absorbed from the combustion region (8030) to other regions distal to the combustion region by thermal conduction.

[0108] U-shaped primary enclosure wall assembly 9A and 9C, an exemplary hot zone enclosure assembly (8042) is shown in a side isometric view. The hot zone enclosure assembly (8042) includes a U-shaped primary enclosure wall assembly (8045) including a combustion zone wall (8060) formed at a cylindrical radius and two opposing primary enclosure side walls (8065, 8070) extending from the edges of the combustion zone wall (8060). The side walls (8065, 8070) each extend from the combustion zone wall along an axis parallel to the gas flow axis (z) to the lower volume (8142) of the cathode chamber, e.g., below the cathode chamber input port (8095). The hot zone enclosure assembly (8042) further includes a fuel input manifold (8015), an optional hot zone enclosure base wall (8075), and two optional hot zone enclosure end walls (8080, 8085). The U-shaped primary enclosure wall assembly (8045) defines a cathode chamber (8055) (shown in cross section in Figures 7A and 7B). The cathode chamber (8055) surrounds the SOFC stack (8005) and combustion region (8030) such that the cathode layers formed on the outer surfaces of each individual fuel cell (8010) are exposed to the cathode chamber (8055). The cathode chamber (8055) is bounded by a U-shaped primary enclosure wall assembly (8045), a fuel input manifold (8015), an optional hot zone enclosure base wall (8075), and optional hot zone enclosure end walls (8080, 8085).

[0109] The cathode chamber (8055) receives a continuous flow of heated cathode gas, in this case a heated air stream, from an external air flow source, for example, from the air delivery control system (198) shown in FIG. 1. The combustion zone (8030) forms the upper volume of the cathode chamber (8055). The lower volume (8142) of the cathode chamber, adjacent the fuel input end (8020), receives the heated air stream (cathode gas) through multiple cathode chamber input ports (8095) shown in FIG. 9B. The intermediate volume (8140) of the cathode chamber extends from the lower volume (8142) of the cathode chamber to the fuel output ends (8025) of each individual fuel cell (8010). The heated cathode gas stream reacts with the cathode layer surfaces of each individual fuel cell (8010) as the heated cathode gas stream passes the exterior surfaces of the individual fuel cells.

[0110] One non-limiting exemplary embodiment of the U-shaped primary enclosure wall assembly (8045) includes a combustion zone wall (8060) formed to surround the combustion zone (8030). The combustion zone wall (8060) provides an upper boundary for the combustion zone (8030) along substantially the entire length of the stack length axis (x) and can extend further beyond the entire stack length. The U-shaped primary enclosure wall assembly (8045) further includes two opposing primary enclosure sidewalls (8065, 8070). Each primary enclosure sidewall (8065, 8070) extends from the combustion zone wall (8060) and is fixedly attached to or integrally formed therewith. Preferably, each primary enclosure sidewall extends the length of the fuel cell stack (8005) from the open fuel output end (8025) to the fuel input end (8020) parallel to the gas flow axis (z).

[0111] Together, the two opposing primary enclosure sidewalls (8065, 8070) and the combustion zone wall (8060) bound the top and opposing sides of the cathode chamber (8055) along the stack length axis (x), as best shown by the cross-sectional view in FIG. 7B. Preferably, the combustion zone wall (8060) and the enclosure sidewall or walls (8065, 8070) are formed as a single element to promote heat transfer throughout. However, if the combustion zone wall (8060) and the enclosure sidewall (8065, 8070) are formed as individual wall elements, the individual elements are bonded in a manner that provides high thermal conductivity across the bonded boundary, for example, using a bonding material with a thermal conductivity coefficient of 100-300 W / m·K.

[0112] 9C , the hot zone enclosure assembly base wall (8075) is mechanically interfaced with the bottom edges of each of the two opposing primary enclosure side walls (8065, 8070). The mechanical interface connection is a welded or soldered connection, although other mechanical interface connection elements can be used, including fasteners, interconnecting fastening elements (e.g., rivets), clips, or interlocking features integrally formed with each of the two opposing primary enclosure side walls (8065, 8070) and / or integrally formed with the hot zone enclosure base wall (8075), or the hot zone enclosure base wall (8075) can be integrally formed with one of the two opposing primary enclosure side walls (8065, 8070). In the first non-limiting embodiment of FIG. 9A, the fuel input manifold (8015) can be mechanically interfaced with the hot zone enclosure base wall (8075), for example, by welding, brazing, soldering, or mechanical fasteners, without necessarily interfacing with one or both of the two opposing primary enclosure side walls (8065, 8070).

[0113] 7A , each of the two opposing primary enclosure assembly sidewalls (8065, 8070) is or can be mechanically interfaced with the fuel input manifold (8015) without the base wall (8075). The mechanical interface between each hot zone enclosure assembly sidewall and the fuel input manifold is a welded or soldered connection, although other mechanical interface connection elements can be used, including separate fasteners and / or fastening elements integrally formed with one or both of the two opposing primary enclosure assembly sidewalls (8065, 8070) and / or integrally formed with the fuel input manifold (8015) in a manner that provides the desired mechanical interface connection. In the second non-limiting embodiment of Figure 7A, when the fuel input manifold (8015) is configured as the lower boundary of the cathode chamber (8055) along the entire length of the stack length axis (x), and possibly even beyond the entire stack length, the hot zone enclosure base wall (8075) is optional. Preferably, the mechanical interface connection between the two opposing primary enclosure assembly side walls (8065, 8070) and the fuel input manifold (8015) forms a gas seal or provides a high impedance to gas flow at the lower boundary of the cathode chamber (8055), preventing cathode air flow from escaping the lower boundary of the cathode chamber (8055).

[0114] Intermediate Enclosure The hot-zone enclosure wall assembly (8042) is mounted inside the intermediate enclosure (9000), as shown in the isometric view of FIG. 8A. The intermediate enclosure is formed, or can be formed, as an airtight gas flow chamber including opposing intermediate enclosure top (9005) and intermediate enclosure bottom (9010) walls, opposing intermediate enclosure side (9015) and intermediate enclosure side (9020) walls, and opposing intermediate enclosure end (9025) and intermediate enclosure end (9030) walls. The intermediate enclosure (9000) includes a fuel access port (9035) for receiving a fuel delivery conduit (8040) therethrough, a cathode input port (9040) for receiving cathode airflow therethrough, and a hot-zone exhaust port (9045) for exhausting exhaust therefrom. Ports (9035), (9040), and (9045) each pass through the walls of the intermediate enclosure as needed to lead to the appropriate gas flow interface connections. In one non-limiting exemplary embodiment, the fuel port passes through one of the side walls (9015, 9020), and the cathode gas input port (9040) and hot zone exhaust port (9045) each pass through the intermediate enclosure top wall (9005).

[0115] The recuperator chamber (9050) and hot-zone exhaust conduit (9055) shown in FIG. 7A are gas flow chambers formed within the intermediate enclosure (9000) and together form a counter-flow gas-to-gas heat exchanger. The recuperator chamber (9050) receives incoming cathode airflow from a cathode airflow source, e.g., air delivery control element (198) shown in FIG. 1, through the cathode input port (9040). Inside the recuperator chamber (9050), the incoming cathode airflow, e.g., air at ambient temperature, is heated by convection and radiation emitted from the walls of the hot-zone exhaust conduit (9055). The heated cathode airflow is forced through the recuperator chamber (9050), exits the recuperator chamber, and reaches the cathode input manifold (9070) through the recuperator outlet port (9065). The cathode air flow source comprises a variable speed air moving device (eg, a fan or blower) that can be controlled to increase or decrease the flow rate of the incoming cathode air flow according to electrical output demands and other process control commands.

[0116] The hot zone exhaust conduit (9055) receives the hot gas mixture from the combustion zone (8030) via the combustion exhaust port (9060). Inside the hot zone exhaust conduit (9055), the hot gas mixture is cooled as energy is convectively and radiatively transferred to the walls of the hot zone exhaust conduit (9055). The hot gas mixture is forced through the combustion exhaust channel (9060) and out of the SOFC system through the hot zone exhaust port (9045) by the action of a controllable, variable speed air moving device (e.g., a fan or blower) to increase or decrease the flow rate of the incoming cathode air stream.

[0117] In the non-limiting exemplary configuration of Figure 7A, the recuperator chamber (9050) is formed inside the hot-zone exhaust conduit (9055), and the two chambers share a common wall (9075). As the hot gas mixture is forced from the combustion zone (8030) into the hot-zone exhaust conduit (9055), the hot gas mixture transfers thermal energy to the shared wall (9075) by radiative emission and convection. The shared wall (9075) then transfers thermal energy to the cathode airflow passing through the recuperator chamber (9050) by convection and radiative emission therefrom. Other gas-to-gas heat exchange configurations can be used without departing from the present technology, including providing multiple heat exchange chambers connected in series or in parallel.

[0118] The recuperator chamber (9050) and hot zone exhaust conduit (9055) are each preferably disposed along the length of the SOFC stack along the stack length axis (x). The cathode input port (9040), and / or hot zone exhaust port (9045), and / or combustion exhaust port (9060) can each be implemented as a single port, as multiple ports, e.g., spaced apart along the stack length axis (x), and / or as one or more openings disposed along the stack length axis (x), e.g., formed as circular, slotted, or other openings that provide gas flow paths. Alternatively, the recuperator chamber (9050) and hot zone exhaust conduit (9055) may be implemented as a single recuperator chamber and a single exhaust chamber, respectively, extending along the stack length axis (x), or as multiple separate recuperator chambers and exhaust chambers arranged in parallel along the stack length axis (x), with each separate chamber having its own cathode input port (9040) and / or hot zone exhaust port (9045).

[0119] In a preferred embodiment, each wall portion of the intermediate enclosure (9000) is fabricated from a ferritic stainless steel, such as Alloy 18 SR® stainless steel, available from Rolled Metal Products, Alsip, Illinois, USA. Alloy 18 SR® stainless steel is preferred because, at SOFC system (8000) operating temperatures and conditions, the added aluminum content advantageously forms a surface layer of aluminum oxide, which prevents oxidation of the exposed surfaces of the intermediate enclosure (9000), which further prevents chromium from leaching from the Alloy 18 SR® stainless steel. In one non-limiting example, Alloy 18 SR® stainless steel has the following approximate chemical composition by weight: carbon 0.015, chromium 18.0, manganese 0.30, silicon 0.60, aluminum 2.0, titanium 0.25, with the remaining weight percent being iron. The thermal conductivity coefficient of Alloy18 SR (registered trademark) stainless steel is approximately 22.8 (W / m K), and the thermal expansion coefficient is 5.9 x 10 -6 (Ft / Ft / °F) or 10.1 x 10 -6 (m / m / °K). The preferred thickness of Alloy 18 SR® stainless steel for at least the peripheral intermediate enclosure walls (9005, 9010, 9015, 9020, 9025, 9030) is 4 mm (0.16 in), although a thickness range of 0.127 mm to 8.0 mm (0.005 to 0.32 in) is usable and may depend on the shape and size of the intermediate enclosure (9000), the forming method used to form the intermediate enclosure (9000), the availability of standard rolled material thicknesses, the desired operating life in hours, etc., without departing from the present technology.

[0120] With regard to material selection, the wall thickness selection may depend on the operating temperature requirements of the walls, the desired operating life of the SOFC system, thermal energy management demands, and / or differences in construction and manufacturing techniques from SOFC system to SOFC system, such that the walls surrounding the intermediate enclosure walls (9005, 9010, 9015, 9020, 9025, 9030) may have a different thickness than the walls forming the hot zone exhaust conduit (9055), recuperator chamber (9050), baffle (9080), and various ports (9040, 9045, 9060). In an alternative exemplary embodiment, at least a portion of the walls of the intermediate enclosure (9000) may comprise a chromium-free high temperature metal alloy such as Monel, which is a nickel-copper alloy with small additions of aluminum and titanium.

[0121] Cathode Input Manifold 7A and 8A, the intermediate enclosure (9000) is formed as a cathode gas flow chamber including a recuperator chamber (9050) and a cathode input manifold (9070). The cathode input manifold receives the cathode air flow coming from the recuperator chamber, which fills the cathode input manifold (9070). The hot zone enclosure assembly (8042) is mounted inside the cathode input manifold (9070), and a U-shaped primary enclosure wall assembly (8045) separates the cathode input manifold from the cathode chamber (8055), except that cathode air flow can pass from the cathode input manifold to the cathode chamber through multiple cathode chamber input ports (8095) positioned adjacent to the open fuel input ends (8020) of each of the multiple SOFC fuel cells to direct the cathode gas flow into the bottom volume of the cathode chamber so that the cathode gas flows within the cathode chamber and passes the entire length of the cathode of each fuel cell along the gas flow axis (z). The cathode input manifold (9070) is bounded by the inwardly facing surfaces of the intermediate enclosure bottom wall (9010), intermediate enclosure side walls (9015, 9020), and intermediate enclosure end walls (9025, 9030), by the outwardly facing surface of the bottom wall (9059) of the hot zone exhaust conduit (9055), and by the outwardly facing surface of the U-shaped primary enclosure wall assembly (8045). The cathode input manifold (9070) receives heated cathode airflow from the recuperator outlet port (9065). Within the cathode input manifold (9070), the heated cathode air stream is further heated by radiation emitted from the U-shaped primary enclosure wall assembly (8045) and intermediate enclosure walls, e.g., (9005, 9010, 9015, 9020, 9025, 9030), shown in FIG. 8A as the heated cathode air stream received from the recuperator outlet port (9065), and by convection due to movement of the cathode air stream through the cathode input manifold. The cathode air stream exits the cathode input manifold (9070) and enters the cathode chamber (8055) through one or more cathode chamber input ports (8095), which pass from the cathode input manifold (9070) into the lower volume (8142) of the cathode chamber (8055).In a preferred embodiment, multiple cathode chamber input ports (8095) pass through each of the primary enclosure side walls (8065, 8070) adjacent their bottom edges. Once within the cathode chamber (8055), the preheated cathode air flows upward from the cathode chamber input ports (8095) into the cathode chamber intermediate volume, where it reacts with the fuel cell exterior surfaces to drive the SOFC reaction. The preheated cathode air then reaches the combustion zone (8030), where the spent cathode air mixes with spent fuel and the mixture is combusted.

[0122] The cathode airflow through the SOFC system (8000) is illustrated in FIG. 7A as a solid black line with a black arrow indicating the direction and path of the cathode airflow. The input cathode airflow is received from an air delivery module (198), which includes a variable speed fan or other air-moving device and a corresponding airflow delivery controller. The cathode airflow passes from the air delivery module (198) to the cathode input port (9040), into the recuperator chamber (9050), and exits the recuperator chamber through the recuperator outlet port (9065) to the cathode input manifold (9070). From the cathode input manifold (9070), the airflow passes through the cathode flow passage (8095) into the cathode chamber lower volume (8142), then passes over the cathode electrode surfaces of each individual fuel cell (8010), and then mixes with the spent fuel exiting the fuel output end (8025) of each individual fuel cell (8010). The spent fuel and spent cathode air are combusted within the combustion zone (8030), further heating the primary enclosure wall assembly (8045). The combusted hot gas mixture passes from the combustion zone (8030) to the hot zone exhaust conduit (9055) and through the combustion exhaust port (9060), then exits the system through the hot zone exhaust port (9045).

[0123] Fuel flow through the SOFC system is also shown in Figure 7A, indicated by dashed black lines and arrows showing the direction of fuel flow and its path. A hydrogen-rich fuel feed mixed with air is received from a supply fuel delivery control system (197), which may include a variable speed fan, pressure regulator, atomizer, or other gas or fluid flow regulation device and a corresponding fuel delivery flow controller. The fuel flow passes from the fuel delivery control system to a fuel reformer (8035), where the supply fuel is reformed to provide a reformate containing fuel, typically hydrogen, carbon monoxide, and carbon dioxide. The fuel flows from the fuel reformer (8035) through a fuel delivery conduit (8040) to a fuel input manifold (8015). Inside the fuel input manifold, the fuel is heated by radiation and convection as it flows through the walls of the input fuel manifold (8015). From the fuel input manifold (8015), fuel flows into the hollow chamber of each individual fuel cell (8010), where it passes through its anode electrode surface and participates in the SOFC reaction. The fuel exits the individual fuel cells through the open output end (8025) and reaches the combustion zone (8030) where the spent fuel mixes with spent cathode air. The spent fuel and spent cathode air are combusted within the combustion zone (8030). The combusted hot gas mixture passes from the combustion zone (8030) through the combustion exhaust port (9060) to the hot zone exhaust conduit (9055) and then exits the system through the hot zone exhaust port (9045). Thermal energy generated by burning the spent syngas and spent cathode air mixture is transferred to the interior of the U-shaped primary enclosure wall assembly (8045). Both the fuel delivery control system (197) and the cathode air delivery module (198) are independently operable to vary the flow rates as needed, e.g., to adjust the current output by varying the fuel flow rate, or to adjust the stack temperature by varying the air flow rate.

[0124] Heat flow diagram and gas flow diagram The thermal energy flow diagram shown in Figure 7B illustrates non-limiting thermal energy transfer patterns enabled by this technology. Solid black lines with black arrowheads pointing inward from the wall surface toward either the cathode or fuel flow region represent radiative emissions from the hot wall surface to the cold gas flow or the cold surface of another wall (e.g., the wall of the intermediate enclosure (9000)). Although not indicated by the flow arrows, convective heat flow from the hot fluid / gas flow to the cold fluid / gas region occurs in each gas flow when the hot gas volume adjacent to the hot wall surface mixes with the cooler gas volume away from the hot surface. Cathode gas flow is indicated by a solid black line with a solid black arrow. Anode gas flow is indicated by a dashed black line with a solid black arrow. As noted above, the fuel and cathode gas streams each enter the cathode chamber (8055) adjacent the input end (8020) of each fuel cell and flow upward toward the combustion zone (8030) where the spent fuel gas and spent cathode gas are mixed and combusted before exiting the cathode chamber through the combustion exhaust port (9060) and into the recuperator chamber (9050). Also, the dashed black line with solid black arrowheads shown inside the thermally conductive core (8200) of the U-shaped primary enclosure wall assembly (8045), described below, indicates the direction and path of heat conduction along the thermally conductive pathway provided thereby. As illustrated, the direction of heat conduction provided by the thermally conductive core (8200) is from the high-temperature combustion zone wall portion (8060) toward the distal ends of each of the side walls (8065, 8070).

[0125] The incoming cathode air stream enters the recuperator chamber (9050) at ambient temperature, and the temperature of the cathode air stream increases as the cathode air stream is heated by heat exchange between the hotter shared wall (9075) and the cooler incoming cathode air stream, as indicated by the arrows pointing from the shared wall (9075) to the recuperator chamber (9050). Inside the cathode input manifold (9070), the temperature of the cathode air stream further increases as the cathode air stream is heated by heat exchange between the hotter U-shaped primary enclosure wall assembly (8045) and the cooler cathode air stream, as indicated by the arrows pointing from the exterior of the U-shaped primary enclosure wall assembly (8045) to the cathode input manifold (9070). Additionally, each of the intermediate enclosure walls (9005, 9010, 9015, 9020, 9025, 9030) is heated by radiative emission from the hot U-shaped primary enclosure wall assembly (8045) and by heat exchange with the cathode air stream. The cathode air stream is further heated by heat exchange between the intermediate enclosure walls and the cathode air stream whenever the temperature of the intermediate enclosure walls is higher than that of the cathode air stream. Alternatively, when the temperature of the intermediate enclosure walls is lower than that of the cathode air stream (e.g., during a start-up cycle), the intermediate enclosure walls are heated by heat exchange between the hot cathode air stream and the intermediate enclosure walls.

[0126] Within the cathode chamber (8055), the temperature of the cathode air stream is further increased by heat exchange between the inner surface of the U-shaped primary enclosure wall assembly (8045), the outer surfaces of the individual fuel cells (8010), and the surfaces of the input fuel manifold (8015) and the cathode gas stream, with the heat flow direction being from a hot surface or hot gas flow region to a cold surface or gas flow region, as indicated by the arrows and cathode air flow directed from the surfaces. Thus, the temperature of the cathode air stream continuously increases as it flows from the cathode chamber flow path (8095), through the cathode chamber, and into the combustion region (8030).

[0127] In a non-limiting example mode of operation, the temperature of the gas mixture within the combustion zone (8030) and at least a portion of the anode surface within the cell is at least 350°C before a steady-state SOFC reaction and DC current output from the SOFC stack (8005) can be maintained. Once a steady-state SOFC reaction is established, the temperature of the gas mixture within the combustion zone (8030) can exceed 500°C. Thus, the gas mixture passing from the combustion zone (8030) through the hot-zone exhaust conduit (9055) to the hot-zone exhaust port (9045) has a temperature much higher than the incoming cathode airflow and higher than the surrounding walls of the hot-zone exhaust conduit (9055). Thus, the temperature of the gas mixture decreases as it passes through the hot-zone exhaust conduit (9055) due to heat transfer via heat exchange between the hot exhaust gas and the walls of the hot-zone exhaust conduit (9055), including the shared wall (9075). The heated walls of the hot zone exhaust conduit (9055), particularly the common wall (9075), cause heat exchange to the cooler incoming cathode air as it flows through the recuperator chamber (9050).

[0128] Referring again to Figure 7B, the incoming fuel-air mixture enters the fuel reformer (8035) at ambient temperature and is heated by partial combustion by a catalytic partial oxidation (CPOX) reactor or fuel reformer (8035). During the CPOX reaction, the temperature of the fuel can peak at around 1200°C. Thus, the temperature of the fuel exiting the fuel reformer (8035) decreases as the fuel passes from the fuel reformer through the fuel conduit (8040) and fuel input manifold (8015) and through each of the fuel cells from the fuel input end (8020) to the fuel output end (8025). Thus, during steady-state operation, after the SOFC reaction that generates the output current is established, the temperature of the fuel stream is likely to decrease continuously along the flow path extending from the fuel reformer (8035) to the input fuel manifold (8015), and then, as the fuel stream passes from the input fuel manifold to the combustion region (8030), it may increase or decrease as heat flows from the fuel stream to cooler surfaces in the surrounding fuel passages, including the walls of the fuel input manifold (8015) and the walls of the fuel cell (8010), which increase their temperature as a result of absorbing heat flow from the fuel stream. In some embodiments, the direction of heat exchange may change, for example, when the temperature of the fuel stream becomes lower than the temperature of the interior walls of the fuel cell. As noted above, the temperature of the gas mixture from the combustion region (8030) continues to decrease as it flows out of the SOFC system.

[0129] Referring again to FIG. 7B, the black dashed lines with black arrows indicate the direction and path of thermal energy transfer by heat conduction from the hotter regions of the thermally conductive core to the colder regions of the thermally conductive core. The thermally conductive core passively reduces the temperature gradient between the core top (8215) and each of the core sidewalls (8205) and (8210). The core top bounds the combustion zone (8030), which, as noted above, has a temperature of at least 350°C and reaches a maximum of approximately 1200°C. Because the gas mixture within the combustion zone is hotter than the surrounding surfaces, heat flows from the gas mixture to the combustion zone wall (8060) by forced thermal convection, and radiant energy absorbed by the combustion zone wall is transferred to each of the sidewalls (8065, 8075) by heat conduction, as described below.

[0130] U-Shaped Hot Zone Enclosure Assembly 7A, 9A, 9B, and 9C, a hot zone enclosure assembly (8042) includes a SOFC stack (8005), a fuel input manifold (8015), and a U-shaped primary enclosure wall assembly (8045). Optionally, the hot zone enclosure assembly (8042) further includes a hot zone enclosure base wall (8075), a first hot zone enclosure end wall (8080), and a second hot zone enclosure end wall (8085). The U-shaped primary enclosure wall assembly (8045) includes a combustion zone wall portion (8060), a first primary enclosure side wall (8065), and a second primary enclosure side wall (8070), both of which are coupled to the combustion zone wall portion.

[0131] Each primary enclosure wall portion (8060), (8065), and (8070) includes a thermally conductive core (8200), which is protected from oxidation by an outer layer applied to its exposed surfaces. The thermally conductive core (8200) includes one or more materials having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K). In a non-limiting exemplary embodiment, the one or more thermally conductive core materials include copper, molybdenum, aluminum, beryllium, iridium, rhodium, silver, tungsten, or alloys or combinations thereof, so that they can be manufactured with the desired thermal conductivity and can reliably meet structural requirements at the operating temperatures of the hot zone. In a preferred embodiment, the thermally conductive core (8200) includes copper or a copper alloy, as described above, having a thermal conductivity of 370 W / m·K at 500°C and 332 W / m·K at 1027°C. The thermally conductive core (8200) preferably has a thickness ranging from 0.127 to 3.2 mm (0.005 to 0.125 inches), although other thicknesses (e.g., 0.5 to 6.0 mm (0.02 to 0.24 inches)) can be used without departing from the present technology. The core thickness can be increased or decreased as needed to meet design requirements. While thicker thermally conductive cores (8200) (e.g., up to 6.0 mm (0.24 inches) or greater) require more thermal energy to heat the core material to the desired operating temperature, increasing the core thickness is beneficial because it increases the rate of thermal energy transfer from one region of the core to another, favorably redistributing the thermal energy more quickly. Other reasons for increasing core thickness include conducting thermal energy over longer distances or achieving a longer operating life when surface oxidation is a likely failure mode. As will be appreciated, the thicker the thermally conductive core (8200), the longer it takes for the thick walls to oxidize to the point where the core becomes unusable. Additionally, aluminum can be used as a core material in SOFC systems capable of producing electrical power when the SOFC system can produce electrical power without exposing the core material to temperatures above about 550°C.

[0132] The thermally conductive core (8200) is a passive element that emits radiation and absorbs radiation in proportion to the fourth power of the absolute temperature difference (in K) between the thermally conductive core and its surroundings, according to the standard blackbody principle. Thermal energy is also transferred to and from the thermally conductive core by thermal conduction from other surfaces of the U-shaped primary enclosure wall assembly (8045) that are in thermally conductive contact. Thermal energy can further be transferred from one region of the thermally conductive core to another region of the thermally conductive core by conduction if there is a thermal conduction path and a temperature difference between the regions.

[0133] In a first non-limiting exemplary embodiment, the thermally conductive core (8200) is a unitary element shaped to surround the SOFC stack (8005) and form a cathode chamber (8055) around the stack. The unitary element is formed from a flat sheet of the core material described above, sized to include three primary enclosure wall portions (8060), (8065), and (8070), and bent to form the U-shaped core element (8200) shown in FIG. 9C. As will be appreciated, the U-shaped core element (8200) can be formed by metal bending fasteners configured to bend the flat metal sheet into the desired U-shape. Other shapes (e.g., rectangular core elements) can be used without departing from the present technology.

[0134] In a second non-limiting exemplary embodiment, the thermally conductive core (8200) includes three separate core portions (8205, 8210, 8215), each including one or more of the core materials described above and each having a wall thickness within the thickness ranges described above. The three separate core portions include two substantially identical side portions (8205) and (8210) and a core top wall portion (8215). The core top wall portion (8215) is formed with a cylindrical radius or the like along its longitudinal length, and the side portions (8205) and (8210) are each formed from a flat metal sheet. The longitudinal dimension along the stack length axis (x) is preferably the same for all three separate core portions. The three separate core portions (8205, 8210, 8215) are joined together, for example, by soldering, brazing, welding, or other mechanical joining techniques, such as by rolling or pressing a mating edge of each side wall with a corresponding mating edge of the core top wall portion (8215), by cladding a sheet of dissimilar metal along the joint between the mating edges of the core portions, or by otherwise fastening a mating edge of each side wall core portion with a corresponding core portion edge of the core top (8215). Regardless of the fastening or joining method, the mechanical interface between the three separate core portions provides a thermal conduction path passing between the core top (8215) and each of the two side core portions (8205) and (8210), preferably along the entire longitudinal length and thickness of the joined core wall portions.

[0135] To prevent oxidation of the thermally conductive core (8200), each core segment (8205, 8210, 8215) is protected by a protective layer applied or attached to the exposed surface of the thermally conductive core (8200). In a first non-limiting exemplary embodiment, the protective layer comprises a nickel plating applied by an electroplating process to a thickness of at least 0.0005 inches and up to 0.002 inches or more. The nickel plating is applied to prevent oxygen diffusion therethrough at operating temperatures of 350 to 1200°C. In a second non-limiting exemplary embodiment, the protective layer comprises an anodized surface formed on the exposed core material. The anodized surface can be formed by controlled electroplating or in an oxygen-rich environment prior to assembly, or the anodized surface can be formed by exposing the protective layer surface to oxygen (i.e., cathode air flow) over time during operation of the SOFC system. In a non-limiting exemplary embodiment, when the core material comprises aluminum or an aluminum-copper alloy, the anodized surface is formed directly on the core material surface. If the anodized surface is formed in a controlled environment prior to assembly by electroplating or an oxygen-rich anodizing process, the desired thickness of the anodized layer is preferably 0.0005 inches, but may range up to about 0.002 inches in some applications to prevent oxygen diffusion through the anodized surface at operating temperatures of 350-1200°C. Regardless of the electroplating process or other anodized layer application type, the thickness of the protective layer will depend on the desired operating life of the SOFC system or thermally conductive core, based on the average and / or peak operating temperatures proximate the thermally conductive core, and based on the oxidant concentration and / or oxidation rate to which the plating thickness will be exposed.

[0136] In a third non-limiting exemplary embodiment, the protective layer includes one or more metal sheets disposed in mating contact with the exposed surfaces of the three core portions (8205), (8210), and (8215). The metal sheets can be attached directly to the uncoated surfaces of the thermally conductive cores or to the electroplated surfaces of the thermally conductive cores. However, as noted above, an electroplated nickel layer can function as the protective layer without a metal sheet. As shown in the exploded isometric view of FIG. 9C, the inner protective sheet metal layer (8220) is fabricated as a U-shaped structure formed to adhere to the inner surfaces of the three core portions (8205), (8210), and (8215), with the inner surface of the inner protective layer (8220) facing the SOFC stack. Preferably, the outer surface of the inner protective layer (8220) facing away from the SOFC stack and the inner surfaces of the three core wall portions (8205, 8210, 8215) are in mating contact over the entire inner surface area of ​​the three core wall portions. The inner protective layer (8220) can extend beyond a portion of the U-shaped thermally conductive core (8200), for example, when the longitudinal length of the inner protective layer (8220) along the stack longitudinal length axis (x) extends beyond the longitudinal length of the thermally conductive core (8200), or when the dimensions of the inner protective layer along the gas flow axis (z) are greater than the dimensions of the thermally conductive core along the same axis, as shown in FIG. 9C, for example, where each of the lower edges (8240, 8245) of the inner protective layer (8220) extends to mate with the hot zone enclosure base wall (8075) or other mechanical interface surface, such as may be provided by the fuel input manifold (8015). Similarly, the side edges of the inner protective layer (8220) can extend beyond the side edges of all three core portions (8205), (8210), (8215), for example, to mate with the end walls (8080) and (8085) of the hot zone enclosure and / or to extend the length of the cathode chamber (8055) along the stack longitudinal axis (x).The inner protective layer (8220) includes an inner upper portion (8225) formed with a cylindrical radius along the stack length axis (x), and two opposing inner sidewall portions (8230) and (8235) each extending from different edges of the cylindrical radius of the inner upper portion (8225).

[0137] The inner protective layer sidewall portions (8230) and (8235), respectively, are attached to the hot zone enclosure base wall (8075) by, for example, a mechanical interface connection between the inner sidewall bottom edges (8240) and (8245) and the primary enclosure base wall (8075) joined along the entire interface connection, for example, by welding, soldering, or other mechanical interface connection configured as a gas seal or configured to provide a high impedance to gas flow. The hot zone enclosure base wall (8075) is also attached to the intermediate enclosure (9000) by its bottom wall (9010) and / or side and end walls (9015, 9020, 9025, 9030), such that the mechanical interface connections between the inner sidewall bottom edges (8240) and (8245) and the primary enclosure base wall securely support the U-shaped primary enclosure wall assembly (8045) within the intermediate enclosure (9000). Alternatively, the inner protective layer sidewall portions (8230) and (8235), respectively, are directly attached to the intermediate enclosure bottom wall (9010) by mechanical interface connections between the inner sidewall bottom edges (8240) and (8245) and the intermediate enclosure bottom wall (9010), which are securely attached by welding, brazing, soldering, or other mechanical interface connections. Alternatively, the sidewall portions (8230) and (8235) are attached to the fuel input manifold (8015) by a mechanical interface connection between the inner sidewall bottom edges (8240) and (8245), respectively, and the fuel input manifold (8015), which are fixedly attached by welding, brazing, soldering, or other mechanical interface connection. In this embodiment, the fuel input manifold (8015) is attached to the intermediate enclosure bottom wall (9010) or other intermediate enclosure wall, so that the mechanical interface connection between the inner sidewall bottom edges (8240) and (8245) and the fuel input manifold (8015) fixedly supports the U-shaped primary enclosure wall assembly (8045) inside the intermediate enclosure (9000).Regardless of the attachment technique, the mechanical interface connection between the inner sidewall bottom edges (8240) and (8245) and the hot zone enclosure base wall (8075), or between the inner sidewall and the input fuel manifold (8015), or between the inner sidewall and the intermediate enclosure bottom wall (9010) preferably provides a gas seal or high impedance to gas flow corresponding to the lower boundary of the cathode chamber (8055). In a preferred embodiment, the inner protective layer sidewall portions (8230) and (8235) each include a plurality of cathode chamber input ports (8095) passing through the inner sidewall portion extending below the bottom edges of the thermally conductive core sidewalls (8205) and (8210) adjacent their bottom edges (8240) and (8245), the input ports (8095) being evenly spaced along the stack length axis (x). The location of the cathode chamber input port (8095) along the gas flow axis (z) is selected to deliver the cathode airflow to the lower volume (8142) of the cathode chamber (8055) proximate the fuel input end (8020). Alternative cathode chamber input port embodiments include a single slotted opening and / or multiple openings of various opening shapes, such as, for example, round, oval, square, rectangular, etc. Alternatively, the cathode chamber input port (8095) can pass through the inner sidewalls (8230, 8235) and core sidewalls (8205, 8210) if the inner surface of the cathode chamber input port (8095) is protected from oxidation, for example, by electroplating or an insert configured to prevent oxidation.

[0138] The outer protective layer (8250) includes two substantially identical outer sidewall portions (8255) and (8260) and an outer top portion (8265). As shown in the exploded isometric view of Figure 9C, the three outer protective layer portions, when joined together and with corresponding outer surfaces of the thermally conductive core (8200), form a U-shaped sheet metal structure shaped to attach to the outer surface of the thermally conductive core (8200) and protect it from exposure to oxygen-rich cathode air flow (e.g., flowing through the cathode air input manifold (9070)). Preferably, the inner surface of the outer protective layer (8250) is in mating contact with the corresponding outer surface of the thermally conductive core (8200) facing away from the SOFC stack. The outer protective layer top wall portion (8265) is formed with a cylindrical radius along the stack length axis (x), and the inner radius of the cylindrical radius of the outer protective layer top wall portion (8260) matches the outer radius of the cylindrical radius of the thermally conductive core top portion (8215) so that when the inner and outer radii are joined together, they provide mating contact therebetween. The outer protective layer sidewall portions (8255) and (8260) are each formed from a flat sheet metal blank cut with a height dimension along the gas flow axis (z) and a length dimension along the stack length axis (x). The height dimension of each sidewall portion (8255, 8260) is selected to underlie or match the corresponding bottom edges of the outer sidewall portions (8270) and (8275) of the thermally conductive core sidewall portions (8205) and (8210). If the cathode flow path (8095) passes only through the inner sidewalls (8230, 8235), the height dimension of the outer sidewalls (8255, 8260) is short enough to prevent the outer sidewalls from obscuring the cathode flow path (8095). In other embodiments, the cathode flow path (8095) can pass through the outer sidewalls (8260, 8255), the core sidewalls (8205, 8210), and the inner sidewalls (8230, 8235). Preferably, the inner surfaces of the outer sidewalls (8255, 8260) and the outer surfaces of the core sidewalls (8205, 8210) are in mating contact after assembly.

[0139] In a preferred embodiment, the wall portions of the inner and outer protective layers are fabricated from a ferritic steel, such as Alloy18 SR® stainless steel, distributed by Rolled Metal Products, Alsip, Illinois, USA. Alloy18 SR® stainless steel is preferred because its added aluminum content advantageously forms a surface layer of aluminum oxide in response to oxygen exposure, which prevents further oxidation of the exposed surfaces of the inner and outer protective layers and prevents chromium leaching from the Alloy18 SR® stainless steel under the operating temperatures and oxygen-rich conditions of SOFC systems (8000). The preferred thickness of Alloy18 SR® stainless steel is 4 mm (0.16 in), although thicknesses ranging from 0.13 to 6.0 mm (0.005 to 0.24 in) can be used without departing from the present technology and may depend on the shape and size of the inner and outer protective layers, the forming method used to form the inner and outer protective layers, the availability of standard rolled thicknesses, the desired operating life in hours, etc. In an alternative exemplary embodiment, the inner and outer protective layers are at least partially comprised of a chromium-free, high-temperature metal alloy such as Monel, a nickel-copper alloy with small additions of aluminum and titanium. The preferred thickness of each wall section is approximately 4 mm (0.16 in), although the actual thickness can range from 0.13 to 6.0 mm (0.005 to 0.24 in) without departing from the present technology.

[0140] The hot-zone enclosure base wall (8075) and the hot-zone enclosure end walls (8080, 8085) can each optionally include a thermally conductive core portion (8200) and two protective layer portions, including an inner protective layer (8280) and an outer protective layer (8285), as shown in the cross-sectional view of FIG. 8B. As with the other protective layers described herein, the inner protective layer (8280) and the outer protective layer (8285) can include nickel plating applied to the exposed surfaces of the thermally conductive core, or the thermally conductive layer can be protected by the inner and outer protective layers, as with the side walls (8230, 8235, 8255, 8260) described above, which are configured to form an anodized layer formed by exposure to cathode air prior to assembly or during operation of the SOFC system. As noted above, the surface of the thermally conductive core (8200) is protected by an electroplating process in which nickel is applied to a thickness ranging from at least 0.0005 inches to a maximum of 0.002 inches or more, and / or by the attachment of sheet metal forms constructed of Alloy18 SR® stainless steel having a thickness of 4 mm (0.16 inches) or a thickness range of 0.13 to 6.0 mm (0.005 to 0.24 inches).

[0141] The thermally conductive core portion (8200) and protective layer portions (8280) and (8285) are configured as the above-described primary enclosure walls (8060), (8065), and (8070), with the thermally conductive core portion (8200) protected from oxidation by the two protective layer portions (8280) and (8285). The thermally conductive core portion (8200) comprises one or more materials having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K).

[0142] More generally, each of the above-described protective layers (8250, 8220) shown in Figure 9C and protective layers (8280, 8285) shown in Figure 8B, as well as the nickel plating and / or anodization layers applied by an electroplating process, are selected to provide a stabilized protective outer layer that prevents oxygen from diffusing through the stabilized protective outer layer. Preferably, the stabilized protective layer does not contain chromium, but the stabilized protective layer preferably prevents chromium from leaching through the stabilized protective layer. Examples of stabilized protective outer layer materials include aluminum oxide, titanium oxide, or other suitable oxide or passivation layers.

[0143] The hot zone enclosure assembly (8042) shown in Figure 9A includes a start-up fuel input conduit (8145) in fluid communication with the fuel delivery control module (197) shown in Figure 1 for delivering a start-up fuel stream (8152) into the start-up fuel input conduit (8145), which is in fluid communication with the combustor element (8155) passing through the combustion region (8030). The fuel igniter element (8160) shown in Figure 7A extends into the combustion region (8030) and is used to ignite the start-up fuel stream (8152) as it exits the combustor element (8155) inside the combustion region during cold start in order to rapidly raise the temperature of the U-shaped primary enclosure wall assembly (8045) and the SOFC stack (8005). The start-up fuel stream (8152) comprises a mixture of hydrogen-rich fuel and unreformed air or unreformed hydrocarbon-rich gas, such as propane. During a cold start of the SOFC system, the fuel delivery control module (197) can deliver the start-up fuel stream (8152) directly to the combustor element (8155) and ignite the fuel exiting the combustor element (8155) using the igniter element (8160). The air delivery module (198) shown in FIG. 1 can also deliver an air stream to the recuperator chamber (9050) to heat it before passing through the cathode input manifold (9070) and the cathode chamber (8055) before reaching the combustion zone (803). Once the U-shaped primary enclosure wall assembly (8045) and the SOFC stack (8005) reach a predetermined startup temperature, the fuel delivery control module can deliver a startup fuel flow (8152) to the combustor element (8155) and supply a fuel flow (8050) to the fuel reformer (8035) to initiate the flow of fuel (8150) through the SOFC stack (8005), while the heated air flow travels through the cathode chamber to ultimately initiate the SOFC reaction.

[0144] Enclosure wall assembly manufacturing process: In a first non-limiting exemplary manufacturing process, the inner protective layer (8220) and the thermally conductive core (8200) are each formed as a single flat sheet from a suitable material as described above. Each flat sheet is cut to predetermined final dimensions corresponding to the final dimensions of the inner protective layer and the thermally conductive core. Additional processing of either sheet is preferably completed while the single flat sheet remains a flat sheet. Additional processing includes at least drilling, punching, or otherwise forming a cathode chamber input port (8095) through the inner protective layer (8220) (or the inner protective layer and core) and adding other holes or formed features, as may be necessary to provide mechanical interface connection elements used to attach the inner protective layer bottom edge (8240, 8245) to the hot zone enclosure base wall (8075), or to attach the inner protective layer bottom edge (8240, 8245) to the input fuel manifold (8015), and / or to attach the inner protective layer bottom edge (8240, 8245) to the intermediate enclosure (9000). Additional holes or configurations may also be added prior to assembling the U-shaped primary enclosure wall assembly (8045) as needed to provide other mechanical interface features, such as for attaching the inner protective layer (8220) to the hot zone enclosure end walls (8080, 8085), or for attaching the inner protective layer (8220) or outer protective layer (8250) to the thermally conductive core (8200), or for providing fuel or cathode air flow ports (e.g., combustion exhaust port (9060)), or for providing access to the fuel delivery conduit (8040), or for providing a fuel conduit to the combustion area for use during cold start, or for providing access to an electrical interface for a sensor mounting point, etc.

[0145] After preparing the flat sheets for assembly, including electroplating, machining, stamping, etc., the inner protective layer (8220) and thermally conductive core (8200) are joined together flat, for example, by aligning and clamping the two sheets into mating contact with one another and bonding the two sheets together to form a composite sheet metal structure that is still a flat sheet. Joining techniques may include welding, brazing, soldering, fastening, e.g., riveting with folded tab joints, self-riveting, or self-clinching, etc.

[0146] If either sheet material is a rolled sheet, the grain direction runs parallel to the rolling direction. Therefore, the rolling direction of each sheet must be identified before cutting and assembling the sheets together, and if the sheets are to be bent, consideration must be given to orienting the grain direction relative to the bending axis. Also, the grain direction of the thermally conductive core may have a different thermal conductivity coefficient than other axes of the core sheet material. Therefore, the thermally conductive core should be oriented with its highest thermal conductivity axis pointing from the core top (8215) to the bottom edge of the core sidewalls (8205, 8210).

[0147] The composite sheet, with the thermally conductive core (8200) and inner protective layer (8220) bonded together in mating contact, is then bent to form the U-shaped structure shown in FIG. 9C , with the inner protective layer facing the SOFC stack. The cylindrical radius has a longitudinal axis aligned with the stack length axis (x). In one non-limiting exemplary embodiment, the bend radius is formed by a hydraulic bending device operable to bend (air bend) or form the composite sheet metal structure at room temperature, such as a press brake. The bend radius that can be achieved without damaging the material or managing undesirable results such as springback is affected by material properties (e.g., hardness, tensile strength, material thickness, material grain direction, etc.), and these properties are taken into consideration when determining the manufacturing process for different embodiments of the U-shaped primary enclosure wall assembly (8045). Generally, it is preferable to bend the material transverse to the material grain direction to avoid cracking of the material and separation of the bonded material layers, but this will vary depending on the material thickness. Composite sheet metal structures can be preheated, e.g., to 90-150°C, before bending to reduce local stresses during bending, thereby helping to prevent material separation and / or undesired deformation. Other forming methods, such as forging at elevated temperatures, can be used without departing from the present teachings.

[0148] In a first non-limiting exemplary manufacturing process, the outer protective layer (8250) is formed from three separate flat sheets of the appropriate sheet material described above. The three separate flat sheets correspond to each of the outer top (8265) and two outer side sections (8255) and (8260). Each flat sheet is cut to predetermined finished dimensions corresponding to the final dimensions of the U-shaped primary enclosure wall assembly (8045). Additional processing on each of the three flat sheets can be completed while the sheet is still flat and before the sheet is cut to final dimensions. Additional processing can include drilling, punching, or otherwise forming passages to provide fuel or cathode air flow ports (e.g., combustion exhaust port (9060)), or passages to provide access to fuel delivery conduits into the combustion area for use during cold startup, or to provide access to electrical interfaces for current collection, sensor mounting points, etc. Additional holes or configurations are added at this point in the manufacturing process as needed to provide other mechanical interface features, such as for attaching the outer protective layer elements (8265, 8255, 8260) to the thermally conductive core (8200) and / or to the hot zone enclosure end walls (8080, 8085), or for attaching the outer protective layer to the inner protective layer as needed.

[0149] After preparing the flat sheet for assembly, including electroplating, machining, punching, etc., the outer top (8265) is bent to form the U-shaped structure shown in FIG. 9C, with the inner radius of the outer top facing the SOFC stack. The cylindrical cylinder has a longitudinal axis along the stack length axis (x) and an inner radius that coincides with the outer radius of the core top (8215). The bend radius is formed by a hydraulic bending device operable to bend (air bend) or form a flat sheet metal structure at room temperature, such as a press brake. The bend radius that can be achieved without damaging the material or managing undesirable results such as springback is affected by material properties (e.g., hardness, tensile strength, material thickness, material grain direction, etc.), and these properties are taken into consideration when determining the manufacturing process for different embodiments of the outer top (8265). Generally, it is preferable to bend the material transverse to the material grain direction to avoid cracking and separation of the bonded material layers, but this varies depending on the material thickness. Composite sheet metal structures can be preheated, e.g., to 90-150°C, before bending to reduce local stresses during bending, thereby helping to prevent material separation and / or undesired deformation. Other forming methods, such as forging at elevated temperatures, can be used without departing from the intended technology.

[0150] After preparing the two flat sheets (8255, 8260) and the curved outer top (8265) for assembly, including machining, punching, etc., each of the three outer protective layers is assembled to the outer surface of the thermally conductive core (8200) and bonded to the thermally conductive core. Bonding techniques may include welding, brazing, soldering, fastening, e.g., with folded tab joints, riveting, self-riveting, or self-clinching, or combinations thereof. As described above, the three outer protective layers are assembled to completely cover the outer surface of the thermally conductive core (8200) and prevent oxidation by the cathode air flow and / or the mixture of spent cathode gas and spent syngas in the combustion zone (8030).

[0151] Manufacturing process: 3 sheets bonded together In a second non-limiting exemplary manufacturing process, the inner protective layer (8220), the thermally conductive core (8200), and the outer protective layer (8250) are each formed as a single flat sheet from their appropriate sheet material, as described above. Each flat sheet is cut to predetermined finished dimensions corresponding to the final dimensions of the U-shaped primary enclosure wall assembly (8045). Additional processing is completed on each of the three single flat sheets while they are still flat sheets. Additional processing includes at least drilling, punching, or otherwise forming a cathode chamber input port (8095) through the inner protective layer (8220) and adding other holes or formed features as needed to provide mechanical interface connection elements used to attach the inner protective layer bottom edge (8240, 8245) to the hot zone enclosure base wall (8075), or to attach the inner protective layer bottom edge (8240, 8245) to the input fuel manifold (8015), and / or to attach the inner protective layer bottom edge (8240, 8245) to the intermediate enclosure (9000). Additional holes or configurations may also be added prior to assembling the U-shaped primary enclosure wall assembly (8045) as needed to provide other mechanical interface features, such as for attaching the inner protective layer (8220) to the hot zone enclosure end walls (8080, 8085), or for attaching the inner protective layer (8220) or outer protective layer (8250) to the thermally conductive core (8200), or for providing fuel or cathode air flow ports (e.g., combustion exhaust port (9060)), or for providing access to the fuel delivery conduit (8040), or for providing a fuel conduit to the combustion area for use during cold start, or for providing access to electrical interfaces for current collection, sensor mounting points, etc.

[0152] After preparing the three flat sheets for assembly, including electroplating, machining, punching, etc., the flat sheets corresponding to the inner protective layer (8220) and outer protective layer (8250) are joined to the flat sheets corresponding to the thermally conductive core (8200), for example, by aligning and clamping the three sheets in mating contact with each other and brazing them together to form a composite sheet metal structure that is still a flat sheet. As described above, the rolling direction of each sheet is identified before cutting and assembling the sheets together, taking into account that the grain direction is oriented relative to the bending axis corresponding to the bending radii of the inner top (8225), core top wall (8215), and outer top (8265). The composite sheet metal structure is then bent to form the U-shaped structure shown in Figure 9C, with the inner protective layer facing the SOFC stack. The cylinder radius has its longitudinal axis aligned with the stack length axis (x). The bend radius can be formed by a hydraulic bending device operable to bend (air bending) or form the composite sheet metal structure at room temperature, such as with a press brake. The bend radius that can be achieved without damaging the material or managing undesirable results such as springback, separation of individual sheets, or cracking along the bending axis is affected by material properties (e.g., hardness, tensile strength, material thickness, material grain direction, etc.), and these properties are taken into consideration when determining the manufacturing process for different embodiments of the U-shaped primary enclosure wall assembly (8045). Generally, bending the material transverse to the material grain direction is preferred to avoid material cracking and separation of bonded material layers, but this varies depending on the material thickness. The composite sheet metal structure can be preheated, e.g., to 90-150°C, before bending to reduce localized stresses during bending, thereby helping to prevent material separation and / or undesired deformation. Other forming methods, such as forging at elevated temperatures, can be used without departing from the subject technology.

[0153] Additional Manufacturing Process Embodiments As described in the first and second manufacturing processes above, any one of the inner protective layer (8220), the thermally conductive core (8200), and the outer protective layer (8250) can be formed from a single flat sheet material including all three sections, including an upper section bent into a cylindrical radius and two side sections extending from opposite edges of the cylindrical radius. According to a further manufacturing process, two or three of the single flat sheet material sections can be joined together by cladding. The cladding can be performed by a single cladding step in which the flat sheets corresponding to the inner protective layer (8220) and the outer protective layer (8250) are each joined to the flat sheet corresponding to the thermally conductive core (8200) in a single cladding or rolling step. Alternatively, the cladding can be performed in a two-step process in which a flat sheet material corresponding to the inner protective layer (8220) or the outer protective layer (8250) is bonded to a flat sheet corresponding to the thermally conductive core (8200), followed by a second cladding step in which the remaining flat sheet material corresponding to the inner protective layer (8220) or the outer protective layer (8250) is bonded to the flat sheet corresponding to the thermally conductive core (8200).

[0154] In the cladding process, the width of the cladding material is transverse to the rolling direction, and therefore the width of the cladding material is preferably selected to correspond to the desired length dimension of the U-shaped primary enclosure wall assembly (8045) along the SOFC stack axis (x).

[0155] From the cladding material, a composite cladding sheet is cut to predetermined finished dimensions corresponding to the formation of the inner protective layer, the thermally conductive core, and the outer protective layer. Additional processing of the composite cladding sheet is completed while the composite cladding sheet is still flat. The additional processing includes at least drilling, punching, or otherwise forming the cathode chamber input port (8095), and further including at least adding other holes or formed features as needed to provide mechanical interface connection elements used to attach the composite cladding sheet to the hot zone enclosure base wall (8075), and / or to the input fuel manifold (8015), and / or to the intermediate enclosure (9000). For example, other holes or features are also added as needed to provide other mechanical interface features, such as for attaching the composite cladding sheet to the hot zone enclosure end walls (8080, 8085), or to provide fuel or cathode air flow ports (e.g., combustion exhaust port (9060)), or to provide access to a fuel delivery conduit (8040), or to provide a fuel conduit to the combustion area for use during cold startup, or to provide access to electrical interfaces for current collection, sensor mounting points, etc. prior to bending the single cladding flat sheet embodiment.

[0156] After preparing the composite cladding sheet, including electroplating, machining, punching, etc., the composite cladding sheet is bent to form the U-shaped structure shown in FIG. 9C with the inner protective layer facing the SOFC stack. The cylindrical radius has a longitudinal axis aligned with the stack length axis (x). The bend radius is formed by a hydraulic bending device operable to bend (air bending) or form the composite sheet metal structure at room temperature, such as a press brake. The bend radius that can be achieved without damaging the material or managing undesirable results such as springback, separation of individual sheets, or cracking along the bending axis is affected by material properties (e.g., hardness, tensile strength, material thickness, material grain direction, etc.), and these properties are taken into consideration when determining the manufacturing process for different embodiments of the U-shaped primary enclosure wall assembly (8045). Generally, it is preferable to bend the composite cladding sheet transverse to the material grain direction to avoid material cracking and separation of the bonded material layers, but this will vary depending on the material thickness. The composite cladding sheet can be preheated, for example, to 90-150°C or up to 1000°C, before bending to reduce localized stresses during bending, thereby helping to prevent material separation and / or undesired deformation.

[0157] As further described in the first and second manufacturing processes above, any one of the inner protective layer (8220), the thermally conductive core (8200), and the outer protective layer (8250) can be formed as three separate flat sheet material elements, each corresponding to a top portion bent into a cylindrical radius and two side portions extending from opposite edges of the cylindrical radius. In the case of the thermally conductive core (8200), the core top portion (8215) and two core sidewall portions (8205, 8210) are manufactured by cutting each from a flat sheet of core material. Then, while the three core portions are still flat, drilling, punching, machining, or electroplating is performed. The core top (8215) is then bent to the desired cylindrical radius, and then the two core sidewall portions (8205, 8210) are attached along the edges of the different cylindrical radii to form the assembled thermally conductive core (8200).

[0158] The inner protective layer (8220) and outer protective layer (8250) are each manufactured in the same manner as the inner top (8225), outer top (8265), and inner sidewall portions (8230, 8235), and outer sidewall portions (8255, 8260) are formed from flat sheets of core material. Then, while the inner and outer protective layer portions are still flat, they are drilled, punched, machined, or electroplated. The inner top (8225) and outer top (8265) are then bent to a desired cylindrical radius, for example, to match the corresponding inner and outer radii of the core top (8215). The inner top (8225) and outer top (8265), and the inner sidewall portions (8230, 8235) and outer sidewall portions (8255, 8260) are then attached to the assembled thermally conductive core, clamped in place, and then soldered, welded, or otherwise mechanically attached to the thermally conductive core.

[0159] As further described in the first and second manufacturing processes above, any one of the inner protective layer (8220), the thermally conductive core (8200), and the outer protective layer (8250) can be formed as separate flat sheet material elements corresponding to all three of the top and two sidewall portions of the final element. Then, while the three separate flat sheet material elements are still flat, drilling, punching, machining, or electroplating is performed. Each of the three separate flat sheet material elements is then bent to the desired cylindrical radius in three independent bending steps. The three previously bent elements are then assembled together and clamped and joined by soldering, welding, or other mechanical fastening elements.

[0160] Heat conduction through the core material 7B and 9C, thermal energy radiating from the combustion region (8030) primarily impinges on the combustion region wall portion (8060), particularly the inner upper wall portion (8225). Gas moving through the combustion region (8030) also primarily transfers thermal energy to the inner upper wall portion (8225) by convection. While the same thermal energy transfer mechanism occurs in each of the inner protective layer side walls (8230, 8235), the rate of thermal energy transfer from the gas within the combustion region wall portion (8060) is greater than the rate of thermal energy transfer from the gas outside the combustion region due to the higher gas temperature within the combustion region (8030). Therefore, the rate of thermal energy transfer to the inner upper wall portion (8225) is greater than the rate of thermal energy transfer to the inner side walls (8230, 8235).

[0161] Thermal energy is transferred from the inner protective layer (8220) to the thermally conductive core (8200) by a combination of thermal conductivity between the mating surfaces of the inner protective layer (8220) and the thermally conductive core (8200) and radiation emitted from the hot surface to the cold surface. Thermal energy is also transferred from the hotter region of the inner protective layer, in this case the inner protective top (8225), to the colder inner sidewalls (8230, 8235) by thermal conduction through the material of the inner layer. Similarly, thermal energy is transferred from the hotter region of the thermally conductive core, in this case the core top (8215), to the colder core sidewalls (8205, 8210) by thermal conduction through the material of the thermally conductive core. However, because the thermally conductive core material has a much higher thermal conductivity coefficient than the material of the inner protective layer (8220), the rate of thermal energy transfer by heat conduction from the core top (8215) to each of the core sidewalls (8205) and (8210) is seven times greater than the rate of thermal energy transfer from the inner protective layer top (8025) to each of the inner protective layer sidewalls (8235) and (8240). The thermally conductive energy flow path from the core top (8215) to each of the core sidewalls (8205) and (8210) is indicated in FIG. 7B by the black dashed lines with backward arrows pointing from the core top (8215) to each of the core sidewalls (8205) and (8210). The transfer of thermal energy from the core top (8215) reduces the temperature gradient that exists in the core material, resulting in a decrease in the temperature of the core top and a corresponding increase in the temperature of the core sidewall portions. Ideally, the increased thermal energy transfer rate of the thermally conductive core passively reduces the temperature gradient between the core top (8215) and the two core side walls (8205) and (8210), thereby reducing the temperature gradient in each of the inner protective layer (8220) and outer protective layer (8250). As the temperature gradient decreases, the entire U-shaped primary enclosure wall assembly (8045) releases heat energy more uniformly along the gas flow axis (z), thereby redistributing the heat energy received from the combustion region (8030) to the cathode air passing through the cathode chamber (8055) and the middle and lower volumes of the cathode input manifold (9070), and to the SOFC tubes (8010) and the walls of the intermediate enclosure.Applicant states that without departing from the present technology, a single core sidewall, such as either core sidewall (8205) or (8210), can be used to provide the desired passive reduction of the temperature gradient between the core top (8215) and the core sidewall only.

[0162] A significant benefit of reducing the temperature gradient along the gas flow axis (z) is the reduction in the temperature gradient along the SOFC stack (8005) along the gas flow (z) axis. Increasing the surface area of ​​the anode and cathode layers maintained at the optimum SOFC reaction temperature increases the yield of the SOFC reaction, for example, as measured by DC current generation per unit of syngas delivery. If only a portion of the anode and cathode surface area is engaged in the SOFC reaction, if the unengaged portion of the anode and cathode surface area is not at the optimized reaction temperature, or if the cathode gas flow is not at the optimized reaction temperature, as described above, the reduction in the temperature gradient tends to convert the unengaged SOFC reaction portion of the SOFC system to engaged, thereby increasing the current output.

[0163] A second benefit is that a more uniform temperature in the SOFC stack along the gas flow axis (z) may reduce damage to the SOFC fuel cells and other components caused by mismatched thermal expansion. The fuel cell is formed from three ceramic layers, each with a different thermal expansion coefficient. Cracking or separation of the three ceramic layers is a common failure mode when the length changes of each material layer along the gas flow axis (z) differ during thermal cycling (e.g., during startup or shutdown). Reducing the temperature gradient along the gas flow axis (z) may reduce damage to the SOFC fuel cells. Similarly, the hot zone enclosure assembly (8042) includes three walls, a thermally conductive core (8200), and two protective layers (8220, 8250) formed from two different materials, each with a different thermal expansion coefficient. Separation and deformation of the three metal layers is a potential failure mode during thermal cycling when the different wall materials expand at different rates. Reducing the temperature gradient variation along the gas flow axis (z) may reduce damage to the U-shaped hot zone enclosure assembly walls during thermal cycling.

[0164] Heat conduction is expressed as the rate of thermal energy transfer (per unit time), also known as heat flow or heat flux, and can be expressed in watts or joules per second. Equation 1 below defines the heat flux, Q, as:

number

[0165] where (Q) is the heat energy transfer rate in watts, (k) is the thermal conductivity coefficient in W / (m K), and (A) is the area of ​​the heat transfer path, e.g., in square meters (m 2), (d) is the length of the conduction path in meters, and (ΔT) is the temperature gradient in degrees Kelvin. For the thermally conductive core of this embodiment, the length of the thermally conductive path (d) is equal to the linear distance from the center of the thermally conductive core top (8215) to the bottom edge of one of the side portions (8205) and (8210). The area (A) dimension is the product of the thickness of the thermally conductive path and the length of the thermally conductive path, for example, along the stack major axis (x).

[0166] In a sample calculation, based on a temperature gradient ΔT of 200°K, a thermal conductivity coefficient of 350 W / (m·K), a core thickness of 2.5 mm (0.0025 m), and a linear dimension (d) of 0.4 m, for example, a unit area of ​​core material, having a square dimension equal to the core thickness, provides a heat flow or heat flux of 1.1 W per unit area, where the unit area is a square with side dimensions of 2.5 mm (0.1 in). If the area dimension exceeds the entire linear dimension of the stack (e.g., 0.61 m or 24 in), the heat flow or heat flux from thermal conductivity will be 267 W through each side wall. By comparison, if the thermal conductivity coefficient of the core material is 50 W / (m·K), the heat flow or heat flux will be 38.0 W through each side wall. Thus, the thermally conductive core of this embodiment potentially provides a seven-fold increase in heat flow through the thermally conductive core (8200) compared to hot zone enclosure walls fabricated from conventional high temperature environment materials (e.g., steel alloys including Hastelloy, Monel, and Inconel) having a thermal conductivity coefficient of 50 W / (m·K) or less.

[0167] Blackbody properties In addition to thermal conduction, the thermally conductive core (8200) has blackbody properties, meaning that the energy radiated per unit surface area per unit time across all wavelengths is proportional to the fourth power of the blackbody's temperature. Blackbody radiation is shown in FIG. 7B and described above, including blackbody energy radiated from the gas flow. In the case of a thermally conductive core, radiation emitted by it tends to be incident on the inner protective layer (8220) and outer protective layer (8250), and radiant energy absorbed by the thermally conductive core tends to be emitted by the inner protective layer (8220) and on the outer protective layer (8250).

[0168] The radiant emittance of a blackbody is described by Equation 2, assuming that the surface emissivity of the radiator is 1, which is likely not the case.

number

[0169] where Q is the rate of heat energy transfer per unit time in watts, and A is the area of ​​the radiating surface in m 2 , σ is the Stephan constant (5.6703×10 -8 W / s 2 K 4 ), T ir is the temperature of the irradiated surface, and Ts is the temperature of the surrounding walls, in Kelvin. As will be appreciated, when thermal energy is conducted by the thermally conductive core (8200) from the core top (8215) to the bottom of the core side walls (8230, 8235), the temperature of the core top decreases while the temperature of the core side walls increases. A change in temperature of both walls changes the radiant emittance of the blackbody at each location in proportion to the fourth power of the temperature difference. In an exemplary comparison, assume that the temperature of the bottom of the primary enclosure side walls (8065, 8070) increases from 650°C (923°K) to 700°C (973°K) as a result of heat conduction through the core, the temperature of the surrounding walls remains unchanged (e.g., 550°C (823°K)), and the area of ​​the radiating surface is 1 square centimeter (1.0 x 10°C) as used above. -4 m 2 ) In this example, the thermal energy transfer rate (radiant emittance) at a temperature of 650°C is 1.514 W. At an increased temperature of 700°C, the thermal energy transfer rate is 2.481 W, which is a 64% increase in radiant emittance per square centimeter.

[0170] Temperature measurements show a decrease in the passive temperature gradient Referring now to Figures 10A, 10B, 11A, and 11B, the passive reduction of the temperature gradient along the gas flow axis (z) of multiple individual fuel cells mounted in a test fixture is illustrated by temperature measurements made with five thermocouple devices. Figure 10A schematically illustrates five SOFC fuel cells (10005) arranged on a test fixture (10000). The SOFC fuel cells are tubular with a cylindrical outer wall surrounding a fluid conduit. An anode surface is formed on the inner diameter of each fuel cell's fluid conduit, and a cathode surface is formed on the outer diameter of each fuel cell. The test fixture includes a fuel input manifold (10010) positioned to support each fuel cell from its bottom end. A flow of syngas is delivered to each tube's fluid conduit by the fuel input manifold. The cathode chamber is formed by enclosing the test fixture fuel cells within a test enclosure designed to provide the same function as the hot-zone enclosure assembly (8042) described above. Two test enclosure units were constructed as described below: the first test enclosure did not include the thermally conductive core of the present technology, and the second test enclosure included the thermally conductive core of the present technology.

[0171] The test fixture contains five thermocouples (TC1-TC5) located at five positions indicated by five stars (10030), as shown in Figure 10A. The five thermocouples (TC1-TC5) are distributed and evenly spaced along the gas flow axis (z). The thermocouples are mounted between the fuel cells (10005) or near the surface of one of the fuel cells. The length of each fuel cell (10005) along the gas flow axis (z) is selected to match the desired fuel cell dimensions (e.g., 150-300 mm (6-12 inches)). Thermocouple TC5 is located approximately 15 mm (0.6 inches) from the top of the SOFC stack, with the remaining thermocouples evenly distributed along the length of the cell. Each thermocouple (TC1-TC5) is electrically interfaced with an electronic controller (not shown). The electronic controller is configured to receive temperature signals from each of the five thermocouples, process the temperature signals (e.g., by comparing the temperature signals with a temperature calibration table), store a series of temperature signals detected by each thermocouple over a period of time, and determine an average temperature value for the given period of time.

[0172] In a first set of temperature measurements, each of the five thermocouples was operated to monitor the temperature at each of the five star positions (10030) throughout a two-and-a-half-hour start-up to cool-down operation cycle, recording temperature data at predetermined time intervals and calculating an average temperature. The first set of temperature measurements was recorded as the test fixture heated from a cold start to an operating temperature corresponding to the production of a current output, recorded for the entire time the test fixture was producing current, and recorded as the test fixture cooled to the cold start temperature. In this example, the operating temperature corresponding to the production of a current output was maintained for approximately one-and-a-half hours, with the start-up and cool-down phases each lasting approximately 30 minutes.

[0173] During the first set of temperature measurements, the test fixture was operated inside the furnace without the thermally conductive core surrounding the stack.

[0174] The first set of temperature measurements is graphically represented in FIG. 10B by the black bars (10035), each representing the average temperature corresponding to one thermocouple during steady-state operation. A dashed line (10050) extends between each black bar (10035) and one of the thermocouples (TC1-TC5) to indicate which thermocouple the average temperature value is associated with. Each temperature measurement corresponding to the black bar (10035) is the average temperature measured by the corresponding thermocouple during the current output by the test fixture. As indicated by the black bars (10035), the average temperature measured at TC1 is approximately 775°C, the average temperature measured at TC2 is approximately 700°C, the average temperature measured at TC3 is approximately 720°C, the average temperature measured at TC4 is approximately 630°C, and the average temperature measured at TC5 is approximately 640°C. The temperatures were averaged over an approximately one-hour operating cycle.

[0175] During the second set of temperature measurements, the test fixture was operated using a second test enclosure assembly including a thermally conductive core. The second test enclosure assembly used the U-shaped primary enclosure wall assembly (8045) described above, including an inner protective layer (8220), a thermally conductive core (8200), and an outer protective layer (8250), as shown in Figure 9C. The inner protective layer (8220) and outer protective layer (8250) of the second test enclosure assembly were formed from Monel, which had a thermal conductivity coefficient of approximately 22.8 (W / m K) and a thickness of approximately 4.0 mm (0.16 in.). The thermally conductive core (8200) of the second test enclosure was formed from a copper alloy with a thermal conductivity coefficient of approximately 350 (W / m K), and the thickness of the thermally conductive core corresponding to the second test enclosure was approximately 3.0 mm (0.12 in.).

[0176] The second set of temperature measurements, corresponding to the second test enclosure, are graphically represented in FIG. 10B by the white-striped bars (10040), each associated with one thermocouple, as indicated by the dashed line (10050) extending between the respective white-striped bar (10040) and one of the thermocouples (TC1-TC5). Each temperature measurement corresponding to the white-striped bar is the average temperature recorded during the period when the test fixture was producing a current output. As indicated by the white-striped bars (10040), the average temperature measured at TC1 is approximately 710°C, the average temperature measured at TC2 is approximately 720°C, the average temperature measured at TC3 is approximately 730°C, the average temperature measured at TC4 is approximately 740°C, and the average temperature measured at TC5 is approximately 710°C.

[0177] As predicted by the above discussion, the temperature gradient along the stack gas flow axis (z) is reduced by adding a copper core to the second test fixture. Temperature measurement data for a first set of temperature values ​​measured using a first test enclosure assembly without a thermally conductive core and a second set of temperature values ​​measured using a second test enclosure assembly (including a thermally conductive core) are listed in Table 1 below. As is readily apparent from the data listed in Table 1 and illustrated graphically in FIG. 10B, adding a thermally conductive core to the second test enclosure assembly reduces the temperature gradient along the gas flow axis (z) of the test fixture fuel cell (10005). Applicant further states that in the second data set corresponding to the second test enclosure assembly including a thermally conductive core, the highest temperature measured was TC4, indicating that the addition of the thermally conductive core indeed shifted the location of the peak temperature away from the combustion region (8030) to a point below the midpoint of the fuel cell.

[0178] [Table 3]

[0179] FIG. 11A graphically illustrates temperature measurement data recorded during a first test cycle using a first test enclosure assembly that does not include a thermally conductive core. The vertical axis of the graphical representation of FIG. 11A corresponds to temperature in degrees Celsius measured by the five thermocouples, and the horizontal axis of FIG. 11A corresponds to time in hours. The graphical representation of FIG. 11A includes five different temperature versus time plots, one plot corresponding to each of the five thermocouple locations. Legend (10045) indicates which data plot corresponds to which thermocouple location (TC1, TC2, TC3, TC4, TC5).

[0180] Similarly, FIG. 11B graphically illustrates temperature measurement data recorded during a second test cycle using a second test enclosure assembly including a thermally conductive core. The vertical axis of the graphical representation of FIG. 11B corresponds to temperature in °C measured by the five thermocouples, and the horizontal axis of FIG. 11B corresponds to time in hours. The graphical representation of FIG. 11B includes five different temperature versus time plots, one plot corresponding to each of the five thermocouple locations. Legend (10055) indicates which data plot corresponds to which thermocouple location (TC1, TC2, TC3, TC4, TC5).

[0181] Comparing the two plots shows that during the start-up cycle, as the thermocouple temperatures rise from 100°C to over 700°C over a period of approximately 30 minutes, the rate of temperature rise at each of the five thermocouple locations is nearly the same when the thermal conductive core is in place (FIG. 11B) but is clearly not the same when the thermal conductive core is not in place (FIG. 11A). This is evident when comparing the start-up period in FIG. 11A with the start-up period in FIG. 11B. FIG. 11A shows that the rate of temperature rise in °C / unit time is greatest at thermocouple location (TC1) and least at thermocouple location (TC5). Conversely, FIG. 11B shows that the rate of temperature rise in °C / unit time is much more uniform at the five thermocouple locations (TC1, TC2, TC3, TC4, TC5) throughout the start-up period.

[0182] If different portions of the individual fuel cells (8010) heat up at different rates, this can lead to cracking and / or chipping of the ceramic layers of the fuel cells and failure of the interface connections between the ceramic and metal components within the stack. Similarly, if different portions of the hot zone enclosure assembly walls heat up at different rates, this can cause delamination and / or buckling of the thermally conductive core and the inner and outer protective layers. Additional SOFC System Embodiments

[0183] Referring now to FIG. 12, a non-limiting exemplary SOFC system (12000) includes two hot-zone enclosure assemblies (12042). The two hot-zone enclosure assemblies are disposed within the intermediate enclosure (9000) shown in FIGS. 9, 16B, and 17, respectively, and are spaced apart along the stack transverse axis (y). Each hot-zone enclosure assembly (12042) includes an SOFC stack (8005), a fuel input manifold (8015) fluidly connected to a fuel reformer (8035) by a fuel delivery conduit (8040), and an L-shaped primary enclosure wall assembly (12045). Each SOFC stack (8005) is enclosed within a different cathode chamber (12055). As shown in Figure 13, each cathode chamber (12055) is bounded in part by one of the L-shaped primary wall assemblies (12045) and in part by a side wall (9015 or 9020) of the intermediate enclosure base wall (9010). Each cathode chamber may also be bounded by opposing primary enclosure end walls (8080, 8085) and the primary enclosure base wall (8075), as shown in Figure 9C.

[0184] FIG. 13 shows two L-shaped primary enclosure wall assemblies (12045), one positioned above a first SOFC stack (8005) and the other positioned above another SOFC stack (8005). As shown in FIG. 13A, each L-shaped primary enclosure wall assembly (12045) is formed of three wall sections: a combustion region curved wall section (12062), a combustion region flat wall section (12064) extending from a first edge of the curved wall section, and a primary enclosure side wall (12070) extending from a second edge of the curved wall section. The combination of the curved wall section (12060) and the combustion region flat wall section (12064) provides an upper boundary for the cathode chamber (12055), described below, and forms an upper boundary for the combustion region (8030) for receiving thermal energy therefrom. The sidewall portion extends from the edge of the curved wall portion and is positioned along the gas flow axis (z) between the SOFC tube output end (8025) and the SOFC tube input end (8020).

[0185] Each L-shaped primary enclosure wall assembly (12045) defines a cathode chamber (12055). The cathode chamber (12055) surrounds the corresponding SOFC stack (8005) and combustion region (8030), such that the cathode layer formed on the outer surface of each individual fuel cell (8010) is exposed to the cathode chamber (12055). The cathode chamber (12055) is partially bounded by the corresponding L-shaped primary enclosure wall assembly (12045), by an intermediate enclosure side wall (9015 or 9020), by the intermediate enclosure bottom wall (9010), or by the fuel input manifold (8015) or another bottom wall (e.g., (8075) shown in FIG. 9C). Each L-shaped primary enclosure wall assembly (12045) defines a different cathode chamber (12055).

[0186] The SOFC system (12000) includes a recuperator chamber (9050) and a hot-zone exhaust conduit (9055), each formed within an intermediate enclosure (9000). The recuperator chamber (9050) and the hot-zone exhaust conduit (9055) together form the countercurrent gas-to-gas heat exchanger described above in the description of Figures 7A and 7B. A cathode airflow at ambient temperature is received into the recuperator chamber (9050) via a cathode input port (9040), and exhaust gas is discharged from the exhaust conduit via a hot-zone exhaust port (9045).

[0187] Within the recuperator chamber (9050), the incoming cathode airflow (e.g., air at ambient temperature) is heated by convection and by radiation emitted from the recuperator chamber walls, particularly the common wall (9075) that separates the hot zone exhaust conduit (9055) from the recuperator chamber (9050). The heated cathode airflow is forced through the recuperator chamber (9050) and exits the recuperator chamber through one or more recuperator outlet ports (9065) to the cathode input manifold (13070). The cathode airflow source includes a variable speed air moving device (e.g., a fan) that can be controlled to increase or decrease the flow rate of the incoming cathode airflow according to electrical output demands and other process control commands.

[0188] The hot-zone exhaust conduit (9055) receives the hot gas mixture from the two combustion zones (8030) via two combustion exhaust ports (9060), each extending from one of the two combustion zones (8030) to the hot-zone exhaust conduit (9055). Inside the hot-zone exhaust conduit (9055), the hot gas mixture is cooled while energy is convectively and radiatively transferred to the walls of the hot-zone exhaust conduit (9055). The hot gas mixture passes from the combustion zones (8030) through the outlet of the SOFC hot zone, through the hot-zone exhaust port (9045), and finally exits the SOFC hot zone through the hot-zone exhaust port (9045).

[0189] Each of the recuperator chambers (9050) and hot-zone exhaust conduits (9055) is preferably positioned along the entire length of the SOFC stack along the stack length axis (x). Each of the cathode input port (9040), hot-zone exhaust port (9045), and two combustion exhaust ports (9060) can be implemented as a single instance of all three ports, for example, located at the center or one end of the stack length along the length axis (x), or multiple cathode input ports (9040), hot-zone exhaust ports (9045), and combustion exhaust ports (9060) can be spaced along the stack length axis (x) to more evenly distribute the cathode airflow to the individual fuel cells and the exhaust gas from the SOFC hot zone. The port openings can be circular, slotted, or other port-shaped instances positioned along the stack length axis (x). Alternatively, each of the recuperator chambers (9050) and hot zone exhaust ducts (9055) can be implemented as a single chamber instance extending along the entire stack length axis (x), or the recuperator chambers and exhaust ducts can be configured as multiple separate chamber and duct instances arranged side by side along the stack length axis (x), each separate chamber instance having its own cathode input port (9040) and / or hot zone exhaust port (9045), and one combustion exhaust port (9060) for each cathode chamber.

[0190] As shown in FIG. 12, a single cathode input manifold (13070) is shared by two cathode chambers (12055). The upper boundary of the cathode input manifold (13070) is defined by the exhaust conduit bottom wall (9059). The side boundaries of the opposing cathode input manifolds are defined by the outer surfaces of the two L-shaped primary enclosure wall assemblies (12045), and the cathode input manifold (13070) has a bottom boundary defined by the intermediate enclosure bottom wall (9010) or the aforementioned separate bottom wall (8070), or both. Each end of the cathode input manifold (13070) can be bounded by the intermediate enclosure end walls (9025, 9030) or the aforementioned end walls (8065, 8085).

[0191] The flow of cathode gas is indicated in Figure 12 by solid streamlines with arrows. The cathode air stream enters through the cathode input port (9040), passes through the recuperator chamber (9050), and then enters the cathode input manifold (13070) through each of the two recuperator outlet ports (9065). Inside the cathode input manifold (13070), the cathode air stream is directed downward from the recuperator outlet port (9065) and enters two sets of cathode chamber input ports (8095), one set of cathode flow paths corresponding to each L-shaped primary enclosure wall (12045). The cathode air then passes from the cathode input manifold (13070) to each of the two cathode chambers (12055). Within the cathode chambers, the cathode gas flows upward past the exposed cathode surfaces of the SOFC stack until it reaches the combustion zone (8030) where the spent cathode air stream is mixed with the spent fuel. The further flow path of the spent fuel and spent cathode air mixture is indicated by the dashed flow lines with arrows showing the mixture flowing from the combustion zone (8030) through two combustion exhaust ports (9060), one for each cathode chamber, through the hot zone exhaust conduit (9055) where the mixture transfers thermal energy to the shared wall (9075) and other wall surfaces, and then exits the SOFC system through the hot zone exhaust port (9045). A combustion zone wall portion (12060), formed by a combustion zone curved wall portion (12062) and a flat combustion zone wall (12264), extends from a different intermediate enclosure side wall (9015) or (9020), respectively, and forms an upper boundary of a corresponding cathode chamber (12055), and a primary enclosure side wall (12070), extending from a second edge of the combustion zone curved wall portion (12062), forms a lateral boundary of the corresponding cathode chamber (12055). The L-shaped primary enclosure wall (12045) is disposed along the entire length of the stack length axis (x) and can extend further beyond the overall stack length dimension.

[0192] 13B and 14 , each L-shaped primary enclosure wall assembly (12045) includes a thermally conductive core (12200) protected by an inner protective layer (12220) and an outer protective layer (12250). The thermally conductive core (12200) is substantially similar in material, structure, function, and thermal properties to the thermally conductive core (8200) discussed herein in connection with FIGS. 7A, 7B, 8B, 9A, 9B, and 9C, and includes a core material having a thermal conductivity coefficient greater than 100 W / (m·K), preferably greater than 200 W / (m·K), such as one or more of copper, molybdenum, aluminum nickel, beryllium, iridium, rhodium, silver, tungsten, or alloys or combinations thereof, so that it can be manufactured with the desired thermal conductivity and can reliably meet structural requirements at the operating temperatures of the hot zone. In one specific exemplary, non-limiting embodiment, the thermally conductive core (12200) comprises a copper mass having a thermal conductivity in the range of approximately 370 W / (m·K) at 500°C and 332 W / (m·K) at 1027°C.

[0193] The L-shaped primary enclosure wall assembly (12045) includes an inner protective layer (12220) and an outer protective layer (12250) configured to protect the thermally conductive core wall (12200) from oxidation. The application of the inner and outer protective layers (12220, 12250) is described above. In a first embodiment, each of the inner and outer protective layers (12220) and (12250) comprises a nickel plating applied to the thermally conductive core (12200) by an electroplating process to a thickness ranging from at least 0.0005 inches to a maximum of 0.002 inches or more. The nickel plating is applied to prevent oxygen diffusion therethrough at operating temperatures of 350 to 1200°C. In a second embodiment, the inner protective layer (12220) comprises an inner sheet metal layer formed to mate with the inner surface of the thermally conductive core (12200), and the outer protective layer (12250) comprises an outer sheet metal layer formed to mate with the outer surface of the thermally conductive core (12200), to prevent oxygen diffusion through either of the protective layers at operating temperatures of 350 to 1200°C.

[0194] The inner and outer protective sheet metal layers are fabricated from the same materials as those described above for the inner protective layer (8220) and outer protective layer (8250) shown in FIG. 9C and described above. In an exemplary, non-limiting embodiment, each of the inner protective layer (12220) and outer protective layer (12250) is formed from a material that is resistant to corrosion and particularly oxidation under SOFC operating conditions. In a preferred embodiment, each of the inner protective layer (12220) and outer protective layer (12250) is fabricated from a ferritic stainless steel, such as Aloly18 SR® stainless steel, available from Rolled Metal Products, Alsip, Illinois, USA. As shown in FIG. 12, the inner protective layer (12220) faces the cathode chamber (12055), and the outer protective layer (12250) faces the cathode input manifold (13070).

[0195] In an exemplary operating mode, thermal energy generated within the combustion region (8030) is transferred to the combustion region wall (12060) by radiation and convection. Thermal energy absorbed by the combustion region wall is passively conducted through the inner protective layer (12220) to the conductive core (12200). Thermal energy reaching the conductive core is passively conducted through the conductive core (12200) to a lower temperature region of the thermally conductive core, for example, to the distal end of the primary enclosure side wall (12070). As a result, the temperature gradient present in the core (12200) is reduced. During steady-state operation, the temperature gradient between the combustion region wall (12060) and the bottom end of the primary enclosure side wall (12070) is reduced. Thermal energy is exchanged between each L-shaped primary enclosure wall assembly (12045) and the SOFC cell (8010) primarily via radiation. However, as the temperature gradient between the combustion zone wall and sidewall decreases, the corresponding temperature gradient along the length of each SOFC cell along the gas flow axis z also decreases. Thermal energy is conducted between the conductive core (12200) and the outer protective layer (12250). Thermal energy exchange via conduction and convection between the outer protective layer (12250) and the cathode gas flowing within the cathode input manifolds (13070, 14070, 15070) heats the cathode gas.

[0196] 13B , in one non-limiting exemplary embodiment, the L-shaped primary enclosure wall assembly (12045) includes an inner protective layer (12220) formed as a single piece of material having an inner sidewall portion (12230), an inner curved wall portion (12225), and an inner top wall portion (12227). The exemplary conductive core (12200) is preferably formed from a single piece of material having a core sidewall portion (12210), a core curved wall portion (12215), and a core top wall portion (12217). As shown in FIG. 13B , the outer protective layer (12250) is formed as three separate portions: an outer sidewall portion (12260), an outer curved wall portion (12265), and an outer top wall portion (12267). The inner protective layer (12220), thermally conductive core (12200), and outer protective layer (12250) can be formed and bonded using any of the methods described in connection with the U-shaped primary enclosure wall assembly (8045), for example, as shown in Figure 9C.

[0197] Referring to FIG. 14 , the SOFC system (14000) includes a single L-shaped hot zone enclosure assembly (14042) enclosing a single SOFC stack (8005) and an input fuel manifold (8015) and fuel delivery conduit (8040). The L-shaped hot zone enclosure assembly (14042) is described above in the description associated with FIGS. 12-13B. The single L-shaped hot zone enclosure assembly (14042) is mounted within an intermediate enclosure (9000) sized to receive the single L-shaped hot zone enclosure assembly (14042). The intermediate enclosure provides a recuperator chamber (9050), a hot zone exhaust port (9045), a cathode input port (9040), a cathode input manifold (14070), and a cathode chamber (12055), all of which are described above. The advantage of the SOFC hot zone (14000) is its compact size.

[0198] Referring to Figure 15, the SOFC hot zone (15000) includes a hot zone enclosure assembly (15042) shown in a schematic diagram. The hot zone enclosure assembly (15042) includes two SOFC stacks (8055), two fuel input manifolds (8015), and U-shaped primary enclosure wall assemblies (8045), each enclosing one of the two SOFC stacks and forming an isolated cathode chamber (8055) surrounding each SOFC stack as described herein in connection with Figures 7A, 7B, 9A, 9B, and 9C. The cathode input manifold (15070) is sized to receive the hot zone enclosure assembly (15042) therein and is bounded by the inward-facing surfaces of the intermediate enclosure side walls (9015, 9020) and intermediate enclosure bottom wall (9010), by the outward-facing surfaces of each of the two U-shaped primary enclosure wall assemblies (8045), by the bottom wall (9059) of the hot zone exhaust conduit (9055), and by the inward-facing surfaces of the hot zone enclosure end walls (8080, 8085) shown in Figure 9C. Intermediate Enclosure

[0199] The hot zone enclosure wall assemblies (12045, 14045, 15042) are each mounted inside the intermediate enclosure (9000) shown in the isometric views of Figures 16b and 17. The intermediate enclosure is formed as a chamber including opposing intermediate enclosure top (9005) and intermediate enclosure bottom (9010) walls, opposing intermediate enclosure side (9015) and intermediate enclosure side (9020) walls, and opposing intermediate enclosure end (9025) and intermediate enclosure end (9030) walls. The intermediate enclosure (9000) encloses a fuel delivery conduit (8040) in a gap between the intermediate enclosure end (9025) and the hot zone enclosure end (8080) wall. The intermediate enclosure includes a cathode input port (9040) for receiving a cathode air flow therethrough and a hot-zone exhaust port (9045) for discharging exhaust therefrom. The intermediate enclosure includes a startup fuel inlet port (8145) for receiving a fuel flow during a startup operating mode of the SOFC system and directing the fuel flow to each of the startup combustor elements (8155). The ports (8145), (9040), and (9045) each pass through the walls of the intermediate enclosure as needed to direct gas flow to interface connections in the receiving region. In one non-limiting exemplary embodiment, the fuel port passes through one of the side walls (9015, 9020), and the cathode gas input port (9040) and the hot-zone exhaust port (9045) each pass through the intermediate enclosure top wall (9005). The intermediate chamber (9000) also surrounds or partially surrounds the recuperator chamber (9050) and the hot zone exhaust conduit (9055), hot zone exhaust port (9045), cathode input port (9040), combustion exhaust ports (9060, 9060a, 9060b), and recuperator outlet port (9065), which function as described in connection with Figures 7A, 7B, and 8A, respectively. Outer enclosure

[0200] As shown in Figures 16A, 16B, and 17, the intermediate enclosure (9000) is preferably installed inside an insulating layer (2012) including a top and bottom (not shown) to insulate the intermediate enclosure surface. The intermediate enclosure and surrounding insulating layers are each installed inside an outer enclosure (16000). In a first non-limiting exemplary embodiment, the outer enclosure (16000) includes two opposing outer enclosure side walls (16015), two opposing outer enclosure end walls (16010), an outer enclosure top wall (16005), and an opposing outer enclosure bottom wall (16002). Preferably, the outer enclosure walls are insulated from the intermediate enclosure (9000). In a preferred embodiment, a thermal barrier (2012) is disposed between the inner enclosure (9000) and the outer enclosure (16000) and is configured to prevent the temperature of the outer wall from exceeding a maximum temperature, e.g., 60°C above ambient temperature. The outer enclosure is formed to provide various input and output ports for interfacing with anode gas fuel and cathode air conduits, an exhaust gas outlet port, power output from the SOFC stack, and interface connections to a control system including temperature and power sensors, fluid flow meters, and other control elements as needed. Preferably, the outer enclosure is formed with structural integrity designed to protect the internal intermediate enclosure, fuel cells, and other internal systems from damage due to impact or moisture, and to prevent contaminants from escaping the SOFC hot zone and / or entering the SOFC hot zone from the outside.

[0201] The outer enclosure (16000) is preferably formed of a metal wall, e.g., steel, stainless steel, aluminum, etc. In some embodiments, the outer enclosure, or a portion of the outer enclosure or elements extending from the inside of the outer enclosure, can be utilized as a heat radiator to radiate thermal energy absorbed from inside the SOFC system (e.g., from a fuel reformer, exhaust gas path, or recuperator) to the air surrounding the SOFC hot zone. All patents, patent applications, and other references disclosed herein are expressly incorporated by reference in their entirety.

[0202] While the technology has been described above with respect to preferred embodiments, those skilled in the art will recognize that it is not limited thereto. Various configurations and aspects of the above technology can be used individually or together. Furthermore, while the technology has been described in the context of its implementation in a particular environment and for a particular application (e.g., a solid oxide fuel cell system), those skilled in the art will recognize that its usefulness is not limited thereto, and that the technology can be beneficially utilized in any number of environments and implementations where it is desirable to increase thermal energy transfer by heat conduction using high thermal conductivity materials in high temperature and corrosive environments. Accordingly, the claims set forth below should be construed in light of the full breadth and spirit of the technology disclosed herein.

Claims

1. 1. A solid oxide fuel cell (SOFC) system comprising: a primary enclosure wall assembly (8045) for balancing temperature; an elongated solid oxide fuel cell (SOFC) stack disposed within said primary enclosure wall assembly (8045); In the solid oxide fuel cell (SOFC) system, The primary enclosure wall assembly (8045) comprises: a combustion zone wall (8060) defining a cathode chamber (8055) in which the SOFC stack is disposed, the cathode chamber (8055) having a combustion zone around an outlet end of the SOFC stack for collecting spent fuel and spent cathode air streams exiting the SOFC stack, the spent fuel and the spent cathode air mixing and combusting within the combustion zone to generate heat, the heat being transferred from the combustion mixture to the combustion zone wall (8060); a first sidewall (8065) ​​extending from the combustion zone wall (8060) along a gas flow axis (z) of the SOFC stack; Including, a cathode input manifold (9070) disposed outside said primary enclosure wall assembly, at least one wall of said cathode input manifold (9070) including both said combustion region wall (8060) and said first side wall (8065); an inner surface of the first sidewall (8065) ​​facing the cathode chamber (8055) and further defining the cathode chamber (8055), an outer surface of the first sidewall (8065) ​​facing the cathode input manifold (9070), the first sidewall (8065) ​​having a distal end adjacent an inlet end of the SOFC stack; the heat absorbed by the combustion zone wall (8060) is thermally conducted to the distal end of the first side wall (8065); A solid oxide fuel cell (SOFC) system in which the heat conducted to the distal end of the first side wall (8065) ​​is radiated from the inner surface of the first side wall (8065) ​​extending from the combustion zone wall (8060), through the cathode chamber (8055), to the inlet end of the SOFC stack, to the inlet end of the SOFC stack, to the outer surface of the cells of the SOFC stack, and is transferred to the cathode air flow in the cathode input manifold (9070) by convection and radiation from the outer surface of the first side wall (8065), lowering the temperature of the combustion zone wall and raising the temperature of the surface of the first side wall (8065) ​​extending from the combustion zone wall (8060) to the inlet end of the SOFC stack.

2. The primary enclosure wall assembly (8045) comprises: a second sidewall (8070) extending from the combustion zone wall (8060) along the SOFC stack gas flow axis (z) opposite the first sidewall (8065); the combustion zone wall (8060) is positioned above the SOFC stack along a SOFC stack lateral width axis (y) transverse to the SOFC stack gas flow axis (z); the second sidewall (8070) has an inner surface facing the cathode chamber (8055) and an outer surface facing the cathode input manifold (9070); the first sidewall (8060) and the second sidewall (8070) face opposite sides of the SOFC stack; the second sidewall (8070) further defines a portion of the cathode chamber (8055); the primary enclosure wall assembly (8045) further includes first and second hot zone enclosure end walls (8080, 8085), which are coupled to each of the first side wall (8065) ​​and the second side wall (8070) to form a hot zone enclosure assembly (8042) including the primary enclosure wall assembly (8045) and the first and second hot zone enclosure end walls (8080, 8085); The solid oxide fuel cell (SOFC) system of claim 1 , wherein the hot zone enclosure assembly (8042) surrounds the SOFC stack inside the cathode chamber (8055).

3. Fuel input manifold (8015), or Hot Zone Enclosure Base Wall (8075), or an intermediate chamber enclosure base wall (9010) arranged to provide a bottom boundary of said cathode chamber (8055); The solid oxide fuel cell (SOFC) system of claim 1 further comprising:

4. 2. The solid oxide fuel cell (SOFC) system of claim 1, wherein the combustion zone wall (8060) and the first side wall (8065) ​​include a thermally conductive core having a thermal conductivity coefficient greater than 100 W / m·K at temperatures greater than 350°C.

5. 3. The solid oxide fuel cell (SOFC) system of claim 2, wherein the combustion zone wall (8060), the first side wall (8065), and the second side wall (6070) are formed as a single element, the single element including a thermally conductive core having a thermal conductivity coefficient greater than 100 W / m·K at temperatures greater than 350°C.

6. 6. The solid oxide fuel cell (SOFC) system of claim 5, wherein the thermally conductive core is fabricated from a material selected from the group consisting of copper and copper alloys, molybdenum, aluminum copper alloys, copper nickel alloys, and combinations thereof.

7. 7. The solid oxide fuel cell (SOFC) system of claim 6, wherein the fuel cell stack shape is selected from the group consisting of oval, square, rectangular, and triangular.

8. The solid oxide fuel cell (SOFC) system of claim 1 , wherein the SOFC stack includes one or more rows of SOFC cells separated by the first sidewall (8065).

9. the combustion zone wall includes a first combustion zone wall (12060) having a first flat wall portion (12064) and a first curved wall portion (12062) extending from the first flat wall portion; the first sidewall includes a first outer sidewall (12070) extending from the first curved wall portion (12062) and surrounding a first row of the at least two rows of SOFC cells; the combustion zone wall includes a second combustion zone wall (12060) having a second flat wall portion (12064) and a second curved wall portion (12062) extending from the second flat wall portion; a second outer sidewall (12070) extending from said second curved wall portion (12062) and surrounding a second row of said at least two rows of SOFC cells; 10. The solid oxide fuel cell (SOFC) system of claim 8, wherein each of the first and second outer sidewalls receives heat from the combustion zone wall by thermal conduction and radiates heat to the inlet end of the SOFC stack.

10. a primary wall assembly (8045) comprising a single element including a combustion zone wall (8060) and one or more side walls (8065), the single element configured to enclose a cathode chamber (8055) therein and configured to provide one or more heat conduction paths extending between different regions of the primary wall assembly; an SOFC stack (8005) surrounded by the primary wall assembly, wherein an inlet end of the SOFC stack (8005) is disposed at the bottom of the cathode chamber and an outlet end of the SOFC stack (8005) is disposed at the top of the cathode chamber, a first portion of the single element receiving heat from a combustion zone surrounded by the primary wall assembly and conducting the heat to a second portion of the single element, and the second portion radiating heat to the first portion of the SOFC stack (8005) within the cathode chamber (8055) and transferring the heat by heat exchange to a cathode airflow passing through a surface of the primary wall assembly outside the cathode chamber (8055); 1. A solid oxide fuel cell (SOFC) system comprising:

11. 1. A hot zone enclosure assembly (8042) for balancing temperatures in a solid oxide fuel cell (SOFC) stack, said hot zone enclosure assembly comprising: a primary enclosure wall assembly (8045), the primary enclosure wall assembly (8045) including a combustion zone wall (8060) defining a combustion zone (8030) around an outlet end of the SOFC stack for collecting anode fuel and cathode air exiting the SOFC stack, the anode fuel and the cathode air combusting in the combustion zone and generating heat, the heat thereby being absorbed by the combustion zone wall; a first sidewall (8065) ​​extending from the combustion zone wall (8065) ​​along the SOFC stack; a thermally conductive core formed as a single element including the combustion zone wall and the first side wall, a first portion of the single element extending along a lateral width axis (y) of the SOFC stack from which a second portion of the single element extends along a gas flow axis (z) of the SOFC stack; Including, the combustion zone wall and the first side wall form a cathode chamber in which the SOFC stack is disposed, the combustion zone being disposed above the cathode chamber and above an outlet end of the SOFC stack; an outlet end of the SOFC stack is disposed in an upper portion of the cathode chamber and an inlet end of the SOFC stack is disposed in a lower portion of the cathode chamber; the combustion zone is located above the cathode chamber above the outlet end of the SOFC stack; the first sidewall has a distal end adjacent an inlet end of the SOFC stack within the cathode chamber; the absorbed heat is transferred by conduction through the single element to the distal end of the first sidewall; A hot zone enclosure assembly (8042) in which the absorbed heat is radiated from the distal end of the first side wall (8065), through the cathode chamber, and to the inlet end of the SOFC stack, balancing the temperature along the SOFC stack.

12. the primary wall assembly (8045) further includes a second sidewall (8070) extending from the combustion zone wall and opposite the first sidewall along a gas flow axis (z) of the SOFC stack; the single element further includes the second sidewall; The hot zone enclosure assembly (8042) comprises: a hot zone enclosure base wall (8075) coupled to said primary enclosure wall assembly (8045), said hot zone enclosure base wall (8075) coupled to said first side wall (8065) ​​and said second side wall (8070); first and second hot zone enclosure end walls (8080, 8085) coupled to the primary enclosure wall assembly (8045), the first and second hot zone enclosure end walls (8080, 8085) coupled to the combustion region wall, the first side wall, and the second side wall to enclose the SOFC stack; 12. The hot zone enclosure assembly (8042) of claim 11, further comprising:

13. The combustion zone wall includes a core top (8215) of a thermally conductive core (8200); the first sidewall comprises a first core sidewall portion (8210) of the thermally conductive core (8200), and the second sidewall (8070) comprises a second core sidewall portion (8205) of the thermally conductive core (8200); 12. The hot zone enclosure assembly (8042) of claim 11, wherein the core top (8215), the first core sidewall portion (8210), and the second core sidewall portion (8205) comprise a single element.

14. 14. The hot zone enclosure assembly (8042) of claim 13, wherein the thermally conductive core (8020) has a thermal conductivity coefficient greater than 100 W / m·K at temperatures greater than 350°C.

15. 14. The hot zone enclosure assembly (8042) of claim 13, wherein the thermally conductive core (8020) is fabricated from a material selected from the group consisting of copper, molybdenum, aluminum copper, copper nickel alloys, and combinations thereof.

16. The hot zone enclosure assembly (8042) of claim 11, further comprising a fuel input manifold (8015) adjacent the inlet end of the SOFC stack.

17. The hot zone enclosure assembly (8042) of claim 11, wherein the SOFC stack is configured to receive a cathode gas from an external air flow source, the cathode gas reacting with the cathode layer surfaces of the fuel cells in the SOFC stack.

18. 20. The hot zone enclosure assembly (8042) of claim 17, wherein the fuel cell stack shape is selected from the group consisting of oval, square, rectangular, and triangular.

19. 12. The hot zone enclosure assembly of claim 11, wherein the SOFC stack is at least two rows of SOFC cells separated by the sidewall.

20. a first outer sidewall extending from the combustion zone wall and surrounding a first row of the at least two rows; a second outer sidewall extending from the combustion zone wall and surrounding a second row of the at least two rows with the sidewall; 20. The hot zone enclosure assembly of claim 19, wherein the first and second outer sidewalls receive heat from the combustion zone wall by thermal conduction and radiate heat to the inlet end of the SOFC stack.

21. 1. A solid oxide fuel cell (SOFC) system comprising: a solid oxide fuel cell (SOFC) stack; an intermediate enclosure assembly (9000); A hot zone (12000; 14000) including a cathode chamber (12055); The SOFC stack is disposed in the cathode chamber (12055), The cathode chamber (12055) a first wall (9015) of said intermediate enclosure assembly (9000) having a thermal conductivity of less than 30 W / (m·K) at 350° C. or higher; a primary enclosure wall assembly (12045) comprising at least one material having a thermal conductivity of 100 W / (m·K) or greater at 350°C or greater; a cathode input manifold (14070) positioned adjacent said primary enclosure wall assembly (12045); and a solid oxide fuel cell (SOFC) system surrounded by.

22. the primary enclosure wall assembly (12045) comprises a combustion zone wall positioned to surround an outlet end of the SOFC stack and a sidewall extending from the combustion zone wall (8060) along the length of the SOFC stack, the sidewall extending from the outlet end toward the inlet end of the SOFC stack; the combustion zone wall is coupled to the first wall of the intermediate enclosure assembly and constructed and arranged to absorb thermal energy generated by combustion of gases within the combustion zone; 22. The solid oxide fuel cell (SOFC) system of claim 21, wherein the sidewalls are constructed and arranged to transfer heat from the combustion zone wall to other portions of the primary enclosure wall assembly by thermal conduction and to transfer thermal energy between the primary enclosure wall assembly and the SOFC stack.

23. 22. The solid oxide fuel cell (SOFC) system of claim 21, wherein the primary enclosure wall assembly is further configured to transfer heat to cathode air flowing through the cathode input manifold.

24. 22. The solid oxide fuel cell (SOFC) system of claim 21, further comprising a thermal insulation layer (2012) disposed adjacent the first wall.

25. 22. The solid oxide fuel cell (SOFC) system of claim 21, wherein a first wall of the intermediate enclosure assembly is made of stainless steel, and the primary enclosure wall assembly includes a wall portion facing the cathode chamber that is made of stainless steel.

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