Fuel cell systems with in-block reforming

Abstract

System that has: a fuel cell block comprising: a fuel cell stack (102) with several solid oxide fuel cells, wherein each solid oxide fuel cell comprises an anode, a cathode and an electrolyte; an in-block fuel feed flow path including a fuel supply manifold (120), a fuel exhaust manifold (118) and one or more fuel delivery channels in fluid communication with the fuel supply manifold (120) and the fuel exhaust manifold (118), each anode being exposed to a fuel flowing in one or more of the fuel delivery channels; and an in-block oxidizer flow path comprising an oxidizer supply manifold (122), an oxidizer exhaust manifold (124), and one or more oxidizer channels in fluid communication with the oxidizer supply manifold (122) and the oxidizer exhaust manifold (124), each cathode being exposed to an oxidizer contained in one or more oxidation channels; an off-block oxidizer flow path comprising: a cathode ejector (114) with an oxidant supply inlet, an oxidizer return inlet and a combined oxidizer outlet; an oxidant supply line in fluid communication with the cathode ejector oxidant supply inlet; an oxidant source (108) in fluid communication with the oxidant supply line; an oxidizer return line in fluid communication with the cathode ejector oxidizer return inlet and the in-block oxidizer flowpath oxidizer exhaust manifold; and a combined oxidant supply line in fluid communication with the combined cathode ejector oxidant output and the in-block oxidizer flowpath oxidant supply manifold; and an off-block fuel flow path comprising: an anode ejector (112) having a fuel supply inlet, a fuel return inlet and a combined fuel outlet; a fuel supply line in fluid communication with the anode ejector fuel supply inlet; a fuel source (110) in fluid communication with the fuel supply line; a fuel return line in fluid communication with the anode ejector fuel return inlet and the in-block fuel feed flowpath fuel exhaust manifold; and a combined fuel supply conduit in fluid communication with the combined anode ejector fuel output and the in-block fuel delivery flowpath fuel supply manifold, wherein the out-of-block fuel flowpath and the in-block fuel delivery flowpath are configured to effect a recirculation ratio in the range of 4.5 to 15 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel delivery inlet. further comprising a pre-reformer (144) in a flow path formed by the combined fuel supply line of the block-external fuel flow path.

Description

Area

[0001] The disclosure relates generally to fuel cell systems and, more particularly, to fuel cell systems with in-block fuel reforming and corresponding methods. background

[0002] A fuel cell stack is an electrochemical system in which a fuel (e.g., hydrogen) is reacted with an oxidizer (e.g., oxygen) at high temperature to generate electricity. The fuel cell stack may comprise multiple fuel cells, each with an anode, a cathode, and an electrolyte. Typically, the fuel cell stack is supported by a system of components, such as reformers, heat exchangers, ejectors, afterburners, fuel and oxidizer sources, and other components. For example, a source of unreformed fuel may be fed to a reformer of the fuel cell system via a fuel ejector.The reformer can partially or completely reform the fuel using a steam process, a dry process, or another reforming technique to produce a reformate that is fed to the anodes of a fuel cell. For example, in steam reforming of natural gas—sometimes called steam methane reforming (SMR)—steam reacts with methane at high temperatures (600°C–1100°C) in the presence of a metal-based catalyst to produce carbon monoxide and hydrogen (CH4 + H2O ⇌ CO + 3H2). With steam reforming, higher hydrocarbons can also be converted through the same process (C2H6 + 2H2O ⇌ 2CO + 5H2), provided these higher hydrocarbons have not already been removed from the process gas stream by another process (e.g., pre-reforming). The fuel cell can expel fuel off-gas from the anode and feed the off-gas into the intake of a fuel ejector or an auxiliary system.

[0003] Additionally, an oxidizer supply provides an oxidant to the fuel cell cathodes. The fuel cell can expel oxidizer exhaust, e.g., unused oxidant, from the cathode. To facilitate reforming of the unreformed fuel, the fuel cell system can provide heat to the reformer by supplying the cathode exhaust or another hot fluid to the reformer. After transferring its heat to the reforming fuel, the cathode exhaust can be supplied to an auxiliary system and / or recycled or recirculated back to the fuel cell cathodes via an oxidizer air ejector.

[0004] The temperature of the recycled and fresh oxidant supplied to the cathodes rises as a result of the heat input as it passes through the fuel cell stack. However, the heat input to the oxidant may be insufficient to maintain the oxidant in thermal equilibrium as it flows through the fuel cell system. This is due, for example, to the relatively large amount of heat input required to support the reforming of the hydrocarbon fuel. To thermally equilibrate the oxidant as it flows through the fuel cell stack, a heat exchanger may be introduced into the fuel cell system, usually upstream of a cathode inlet. Combustion products may be fed to the heat exchanger to initiate a reaction that produces heat. Combustion products may include fuel off-gas, such as unconsumed fuel, and cathode off-gas.The reaction can take place in the heat exchanger or in another component, such as an afterburner located upstream of the heat exchanger.

[0005] In this configuration, the oxidant is typically maintained in thermal equilibrium as it flows through the fuel cell system during normal operation. The heat generated in the fuel cell stack, the heat transferred to the fuel in the reformer, the cooling effect of the oxidant mixing at the cathode ejector, and the heat input from a heat exchanger balance each other to maintain this thermal equilibrium; indeed, a heat exchanger upstream of the cathode inlet is sized for this purpose.

[0006] One type of fuel cell is the solid oxide fuel cell (SOFC). The basic components of an SOFC can include an anode, a cathode, a solid electrolyte, and an interconnector. The fuel can be supplied to the anode, and the oxidant can be supplied to the fuel cell's cathode. At the cathode, electrons ionize the oxidant. The electrolyte can comprise a material that allows the ionized oxidant to pass through it to the anode while remaining impermeable to the fluid fuel and oxidant. At the anode, the fuel combines with the ionized oxidant in a reaction that releases electrons, which are conducted back to the cathode via the interconnector. Heat generated from ohmic losses is removed from the fuel cell through a fuel (i.e., anode) exhaust or an oxidant (i.e., cathode) exhaust, or heat is radiated to the environment.

[0007] The anode of an SOFC can be a mixed cermet comprising nickel and zirconium oxide (e.g., yttrium-stabilized zirconia (YSZ)) or nickel and cerium oxide (e.g., gadolinia-doped ceria (GDC)). Nickel and other materials can function to not only facilitate the chemical reaction between the fuel and the ionized oxidant, but can also have catalytic properties that enable the anode to reform a hydrocarbon fuel within the fuel cell. One method for reforming the hydrocarbon fuel is steam reforming of methane (CH4), an endothermic reaction (Equation 1): CH4 + H2O → CO + 3H2 ΔH° = 206.2 kJ / mol (Equation 1)

[0008] Alternative reforming processes are also available. For example, the hydrocarbon fuel can be reformed by carbon dioxide reforming (also known as dry reforming) (Equation 2): CO2 + CH4 → 2H2 + 2CO (Equation 2)

[0009] For example, an SOFC can be constructed as a segment-in-series or in-plane-series arrangement of individual cells. Typically, the oxidant is introduced at one end of the row of fuel cells via an oxidant inlet and flows over the remaining fuel cells until it reaches a cathode exhaust outlet. Each fuel cell transfers heat to the oxidant, causing its temperature to rise. A temperature gradient can develop within the fuel cell, increasing from the oxidant inlet to the oxidant exhaust outlet. These temperature gradients can cause thermal stresses on the fuel cell, which can lead to material degradation or failure of fuel cell components. In addition, thermal stresses on the fuel cell can reduce fuel cell performance.Some fuel cell systems attempt to mitigate this problem by using in-block reforming (IBR), which reforms a portion of the fuel within the fuel cell stack. However, these systems typically still require a reformer and a heat exchanger. Thus, there are opportunities for improvements to fuel cell systems configured for in-block reforming.

[0010] WO 2015 / 155 540 A1 describes a fuel cell system with improved thermal management. US 2008 / 0 107 932 A1 describes methods for generating electricity using a solid oxide fuel cell. Summary

[0011] The present invention is defined by independent claims 1 and 10; the dependent claims describe embodiments of the present invention.

[0012] According to some embodiments of the disclosure, a fuel cell system is provided. The fuel cell system may include a fuel source and an oxidant source. The fuel cell system further includes a fuel cell stack configured for IBR, an anode ejector, and a pre-reformer. The fuel cell stack may include a plurality of fuel cells, each fuel cell including an anode, a cathode, and an electrolyte. The fuel cells may be SOFCs. The fuel cell stack may further include a fuel supply manifold, a fuel exhaust manifold, an oxidant supply manifold, and an oxidant exhaust manifold. The fuel supply manifold may be configured to receive fuel and supply the fuel to the anodes of the plurality of fuel cells.The fuel exhaust manifold may be configured to expel fuel exhaust from the fuel cell stack. The oxidant supply manifold may be configured to receive an oxidant and supply the oxidant to the cathodes of the plurality of fuel cells, and the oxidant exhaust manifold may be configured to expel oxidant exhaust from the fuel cell stack.

[0013] The anode ejector of the fuel cell system may be configured to receive fuel from a fuel source, receive a portion of exhaust gas from the fuel cell stack, and deliver a fuel stream comprising at least a portion of the received fuel and / or the received portion of the exhaust gas. In some examples, the anode ejector is configured to deliver the fuel stream based on a recycle ratio of at least 7.5 (i.e., 750%). The recycle ratio is the ratio (by mass) of the amount of the received portion of the recycled fuel, in this example, the fuel exhaust gas, to the amount of received fuel provided as a fuel stream. In some examples, the anode ejector is configured to deliver the fuel stream based on a recycle ratio range between 4.5 and 15 (i.e., 450% and 1500%).In other examples, the anode ejector is configured to deliver the fuel stream based on a recirculation ratio range between 6 and 8 (i.e., 600% and 800%). In some examples, the anode ejector is configured to receive a portion of fuel exhaust from the fuel cell stack without passing through a heat exchanger.

[0014] As previously mentioned, the fuel cell system may also include a pre-reformer. The pre-reformer may be disposed between an outlet of the anode ejector and the fuel supply manifold and may be configured to remove higher hydrocarbons from the fuel stream received by the anode ejector. The pre-reformer may also be configured to supply the pre-reformed fuel to the fuel supply manifold. In some examples, the pre-reformer supplies the pre-reformed fuel directly to the fuel supply manifold. In some examples, the pre-reformer may be an adiabatic catalytic converter configured to remove the higher hydrocarbons from the fuel stream from the anode ejector without any heat input other than heat.

[0015] In some embodiments, the fuel cell system may also include an auxiliary ejector. For example, the auxiliary ejector may be configured to receive a portion of fuel exhaust from the fuel cell stack and oxidant exhaust from the oxidant exhaust manifold. In some embodiments, the fuel cell system may also include an afterburner configured to receive fuel exhaust from the fuel cell stack as well as oxidant exhaust from the auxiliary ejector. In some embodiments, the fuel cell system may also include a turbine configured to receive exhaust from the afterburner.

[0016] In some examples, the fuel cell system includes a heat exchanger located upstream or downstream of the cathode ejector. The heat exchanger can transfer heat from the auxiliary ejector exhaust to the oxidant supply. In some examples, the fuel cell system does not include heat exchangers.

[0017] In some embodiments, the fuel cell system may include a compressor configured to receive oxidant from the oxidant source. In some embodiments, the fuel cell system may also include a cathode ejector, where the cathode ejector may be configured to receive oxidant from the compressor, receive oxidant exhaust from the oxidant exhaust manifold of the fuel cell stack, and supply the received oxidants in varying proportions to the oxidant inlet manifold of the fuel cell stack. In some examples, the oxidant exhaust from the cathode ejector is supplied to the oxidant inlet manifold of the fuel cell stack without passing through a heat exchanger.

[0018] According to some embodiments of the disclosure, a solid oxide fuel cell system is provided. The solid oxide fuel cell system may include an IBR-configured solid oxide fuel cell stack including at least one solid oxide fuel cell, each solid oxide fuel cell including an anode, a cathode, and an electrolyte.

[0019] Further, the solid oxide fuel cell system may include an anode loop for supplying fuel and reformate to the anode of each solid oxide fuel cell. The anode loop may include a fuel inlet manifold, a fuel exhaust manifold, a fuel source, an anode ejector, and a pre-reformer. The fuel inlet manifold may be configured to supply fuel to the anode of each solid oxide fuel cell. The fuel exhaust manifold may be configured to receive fuel exhaust, e.g., unused fuel or partially depleted reformed fuel, from the anode of each solid oxide fuel cell. The anode ejector may be configured to receive fuel from the fuel source and the fuel exhaust manifold and supply a fuel stream comprising at least a portion of the received fuels from the fuel source and / or the fuel exhaust manifold.In some examples, the anode ejector is configured to supply the fuel stream based on a recycle ratio of at least 7.5. In some examples, the anode ejector supplies a fuel stream containing less than about 11% methane based on the recycle ratio, for example, 7.5. The pre-reformer may be disposed between an outlet of the anode ejector and the solid oxide fuel cell stack and may be configured to remove higher hydrocarbons from the fuel stream received by the anode ejector.

[0020] Additionally, the solid oxide fuel cell system may include a cathode loop for supplying oxidant to the cathode of each solid oxide fuel cell. The cathode loop may include an oxidant inlet manifold, an oxidant exhaust manifold, and an oxidant source. The oxidant inlet manifold may be configured to supply oxidant to the cathode of each solid oxide fuel cell, and the oxidant exhaust manifold may be configured to receive oxidant exhaust from each cathode of the solid oxide fuel cells.

[0021] In some embodiments, the solid oxide fuel cell system includes a compressor configured to receive oxidant from the oxidant source. In some examples, the cathode loop may also include a cathode ejector. The cathode ejector may be configured to receive oxidant from the compressor, receive oxidant exhaust from the oxidant exhaust manifold of the fuel cell stack, and supply the received oxidants in varying proportions to the oxidant inlet manifold of the fuel cell stack.

[0022] Furthermore, the solid oxide fuel cell system may include an auxiliary loop for combusting a portion of the fuel exhaust from the fuel exhaust manifold and a portion of the oxidant exhaust from the oxidant exhaust manifold. In some examples, the auxiliary loop may include an auxiliary ejector and an afterburner. The auxiliary ejector may be configured to receive a portion of the oxidant exhaust from the oxidant exhaust manifold, a portion of oxidant from the oxidant source, and a portion of fuel exhaust from the fuel exhaust manifold. The afterburner may be configured to receive the exhaust from the auxiliary ejector. In some embodiments, the solid oxide fuel cell system includes a turbine configured to receive the exhaust from the afterburner.

[0023] In some embodiments, a fuel cell system is provided that includes a fuel cell block, an off-block oxidant flowpath, and an off-block fuel flowpath. The fuel cell block includes a fuel cell stack having a plurality of solid oxide fuel cells, each solid oxide fuel cell having an anode, a cathode, and an electrolyte. The fuel cell block may also include an on-block fuel delivery flowpath including a fuel supply manifold, a fuel exhaust manifold, and one or more fuel delivery channels in fluid communication with the fuel supply manifold and the fuel exhaust manifold, each anode being exposed to fuel flowing in one or more of the fuel delivery channels.Further, the fuel cell block may include an in-block oxidizer flow path including an oxidizer supply manifold, an oxidizer exhaust manifold, and one or more oxidizer channels in fluid communication with the oxidizer supply manifold and the oxidizer exhaust manifold, each cathode being exposed to an oxidizer flowing in one or more oxidizer channels.

[0024] The off-block oxidizer flowpath may include a cathode ejector having an oxidizer supply inlet, an oxidizer return inlet, and a combined oxidizer outlet. For example, the combined oxidizer outlet may provide a mixture of oxidant received via the oxidizer supply inlet and recirculated oxidant received via the oxidizer return inlet. The off-block oxidizer flowpath may also include an oxidizer supply line in fluid communication with the cathode ejector oxidizer supply inlet, an oxidizer source in fluid communication with the oxidizer supply line, an oxidizer return line in fluid communication with the cathode ejector oxidizer return inlet, and the on-block oxidizer flowpath oxidizer exhaust manifold.Further, the block-external flow path may include a combined oxidant supply line in fluid communication with the combined cathode ejector oxidant outlet and the block-internal oxidizer flow path oxidant supply manifold.

[0025] The off-block fuel flow path may include an anode ejector having a fuel supply inlet, a fuel return inlet, and a combined fuel outlet. For example, the combined fuel outlet may provide a combined fuel based on fuel received via the fuel supply inlet and recirculated fuel received via the fuel return inlet.The off-block flow path may also include a fuel supply line in fluid communication with the anode ejector fuel supply inlet, a fuel source in fluid communication with the fuel supply line, a fuel return line in fluid communication with the anode ejector fuel return inlet and the on-block fuel feed flow path fuel exhaust manifold, and a combined fuel supply line in fluid communication with the combined anode ejector fuel outlet and the on-block fuel feed flow path fuel supply manifold.

[0026] In some examples, the off-block fuel flow path, together with the on-block fuel feed flow path, are configured to provide a recirculation ratio in the range of 6:1 to 8:1 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel supply inlet. In other examples, the off-block fuel flow path, together with the on-block fuel feed flow path, are configured to provide a recirculation ratio in the range of 4.5:1 to 15:1 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel supply inlet.In still other examples, the off-block fuel flow path together with the on-block fuel feed flow path are configured to provide a recirculation ratio of about 7.5:1 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel feed inlet.

[0027] In some examples, the off-block fuel flowpath, together with the on-block fuel delivery flowpath, are configured to effect a weight percentage of methane in a fluid flowing into the on-block fuel delivery flowpath fuel supply manifold of no more than eleven percent. In some examples, the off-block fuel flowpath, together with the on-block fuel delivery flowpath, are configured to effect a weight percentage of methane in a fluid flowing into the on-block fuel delivery flowpath fuel supply manifold in the range of 0 to 11 percent.

[0028] In some examples, the fuel cell system includes an off-block auxiliary flowpath having an auxiliary ejector with an oxidant supply inlet, a fuel exhaust inlet, an oxidant exhaust inlet, a recirculation inlet, and an outlet. The auxiliary flowpath further includes an oxidant supply line in fluid communication with the auxiliary ejector oxidant supply inlet and the oxidant source; a fuel exhaust line in fluid communication with the auxiliary ejector fuel exhaust inlet and the on-block fuel delivery flowpath fuel exhaust manifold; an oxidant exhaust line in fluid communication with the auxiliary ejector oxidant exhaust inlet and the on-block oxidizer flowpath oxidizer exhaust manifold; an auxiliary exhaust line in fluid communication with the auxiliary ejector exit; and a recirculation line in fluid communication with the auxiliary ejector return inlet and the auxiliary exhaust line.

[0029] In some examples, the auxiliary flow path includes an afterburner. In some examples, the fuel cell system includes a heat exchanger for transferring heat energy between a fluid outlet of the afterburner and a fluid flowing in the combined oxidant supply line. In some examples, the heat exchanger is located between a fluid outlet of the afterburner and a fluid flowing in the oxidant supply line.

[0030] According to some embodiments of the disclosure, a fuel cell system includes a fuel cell stack configured for IBR, having a plurality of chambers (e.g., segments). Further, the fuel cell system may utilize a plurality of anode ejectors and pre-reformers. The fuel cell system may also include a fuel source and an oxidant source. Furthermore, the fuel cell system may include a first anode ejector, a second anode ejector, a first pre-reformer, and a second pre-reformer. The fuel cell stack may include a plurality of fuel cells, each fuel cell including an anode, a cathode, and an electrolyte. The fuel cells may be SOFCs.

[0031] Each chamber of the fuel cell stack may include a fuel supply manifold and a fuel exhaust manifold. One chamber of the fuel cell stack may include an oxidant supply manifold, and another chamber of the fuel cell stack may include an oxidant exhaust manifold. The fuel supply manifold of each fuel cell stack may be configured to receive fuel and supply the fuel to the anodes of the plurality of fuel cells. The fuel exhaust manifold of each fuel cell stack may be configured to expel fuel exhaust from the fuel cell stack.The oxidant supply manifold of one chamber of the fuel cell stack may be configured to receive an oxidant and supply the oxidant to the cathodes of the plurality of fuel cells, and the oxidant exhaust manifold of another chamber of the fuel cell stack may be configured to exhaust the oxidant from the fuel cell stack.

[0032] A first anode ejector of the fuel cell system may be configured to receive fuel from the fuel source, receive a portion of fuel off-gas from a chamber of the fuel cell stack, and supply a first fuel stream comprising at least a portion of the received fuel and / or the received portion of the fuel off-gas. For example, the first fuel stream may be supplied to a first pre-reformer. In some examples, the first anode ejector is configured to receive a portion of the fuel off-gas from a chamber of the fuel cell stack without passing through a heat exchanger.

[0033] The first pre-reformer may be disposed between an outlet of the first anode ejector and the fuel supply manifold and may be configured to remove higher hydrocarbons from the first fuel stream received by the first anode ejector. In some examples, the first pre-reformer may be an adiabatic catalytic converter configured to remove the higher hydrocarbons from the fuel stream from the first anode ejector without any heat input other than heat.

[0034] A second anode ejector of the fuel cell system may be configured to receive fuel from the fuel source, receive a portion of fuel exhaust from another chamber of the fuel cell stack, and supply a second fuel stream comprising at least a portion of the received fuel and / or the received portion of the fuel exhaust. For example, the second fuel stream may be supplied to a second pre-reformer. In some examples, the second anode ejector is configured to receive a portion of the fuel exhaust from the other chamber of the fuel cell stack without passing through a heat exchanger.

[0035] The second pre-reformer may be disposed between an outlet of the second anode ejector and the fuel supply manifold and may be configured to remove higher hydrocarbons from the second fuel stream received by the second anode ejector. In some examples, the second pre-reformer may be an adiabatic catalytic converter configured to remove the higher hydrocarbons from the fuel stream from the second anode ejector without any heat input other than heat.

[0036] In some examples, the first anode ejector is configured to deliver the first fuel stream based on a recirculation ratio of at least 7.5. In some examples, the first anode ejector is configured to deliver the first fuel stream based on a recirculation ratio range between 7.5 and 15. Similarly, in some examples, the second anode ejector is configured to deliver the second fuel stream based on a recirculation ratio of at least 7.5. In some examples, the second anode ejector is configured to deliver the second fuel stream based on a recirculation ratio range between 7.5 and 15.

[0037] In some embodiments, the first anode ejector and the second anode ejector are configured to supply the first fuel stream and the second fuel stream at respective recycle ratios such that the first fuel stream and the second fuel stream provide a combined fuel containing less than about 11% methane. For example, the first anode ejector may be configured to supply the first fuel stream based on a first ratio of the received first portion of exhaust gas to the received fuel, and the second anode ejector may be configured to supply the second fuel stream based on a second ratio of the received portion of exhaust gas to the received fuel. In some examples, the first ratio and second ratio may each be in the range of 7.5 to 15.

[0038] In some embodiments, the fuel cell system may also include an auxiliary ejector. For example, the auxiliary ejector may be configured to receive a portion of fuel exhaust from the fuel cell stack and the oxidant removed from the oxidant exhaust manifold. In some embodiments, the fuel cell system may also include an afterburner configured to receive fuel exhaust from the fuel cell stack as well as oxidant removed from the auxiliary ejector. In some embodiments, the fuel cell system may also include a turbine configured to receive the exhaust from the afterburner.

[0039] In some examples, the fuel cell system includes a heat exchanger located upstream or downstream of the cathode ejector. The heat exchanger may transfer heat from the auxiliary ejector exhaust gas to the oxidant supply. For example, the heat exchanger may be configured to receive the auxiliary ejector exhaust gas and receive oxidant supplied from the cathode ejector. The heat exchanger may then transfer heat from the auxiliary ejector exhaust gas to the oxidant supply and provide it to the oxidant inlet manifold of the fuel cell stack. Alternatively, the heat exchanger may be configured to receive oxidant from the oxidant source, transfer heat from the auxiliary ejector exhaust gas to the oxidant, and supply the oxidant to the cathode ejector.

[0040] In some examples, a fuel cell system is provided that includes a fuel cell block, an off-block oxidant flow path, a first off-block fuel flow path, and a second off-block fuel flow path. The fuel cell block may include a fuel cell stack having first and second segments, each segment including a plurality of solid oxide fuel cells, each solid oxide fuel cell including an anode, a cathode, and an electrolyte.The fuel cell block may also include a first in-block fuel feed flowpath including a first fuel supply manifold, a first fuel exhaust manifold, and one or more first fuel feed channels in fluid communication with the first fuel supply manifold and the first fuel exhaust manifold, wherein each anode in the first segment is exposed to a fuel flowing in one or more of the first fuel feed channels. Further, the fuel cell block may include a second in-block fuel feed flowpath including a second fuel supply manifold, a second fuel exhaust manifold, and one or more second fuel feed channels in fluid communication with the second fuel supply manifold and the second fuel exhaust manifold, wherein each anode in the second segment is exposed to a fuel flowing in one or more of the second fuel feed channels.The fuel cell block may also include an in-block oxidizer flow path including an oxidizer supply manifold, an oxidizer exhaust manifold, and one or more oxidizer channels in fluid communication with the oxidizer supply manifold and the oxidizer exhaust manifold, wherein each cathode in the first and second segments is exposed to an oxidizer flowing in one or more oxidizer channels.

[0041] The off-block oxidizer flowpath may include a cathode ejector having an oxidant supply inlet, an oxidant return inlet, and a combined oxidizer outlet. Further, the off-block oxidizer flowpath may include an oxidant supply line in fluid communication with the cathode ejector oxidant supply inlet, an oxidant source in fluid communication with the oxidant supply line, and an oxidizer return line in fluid communication with the cathode ejector oxidant return inlet and the on-block oxidizer flowpath oxidizer exhaust manifold. The off-block oxidizer flowpath may also include a combined oxidizer supply line in fluid communication with the combined cathode ejector oxidizer outlet and the on-block oxidizer flowpath oxidizer supply manifold.

[0042] The first off-block fuel flowpath may include a first anode ejector having a fuel supply inlet, a fuel return inlet, and a combined fuel outlet. The first off-block fuel flowpath may also include a first fuel supply conduit in fluid communication with the first anode ejector fuel supply inlet, a fuel source in fluid communication with the first fuel supply conduit, and a first fuel return conduit in fluid communication with the first anode ejector fuel return inlet and the second on-block fuel delivery flowpath fuel exhaust manifold. Further, the first off-block fuel flowpath may include a first combined fuel supply conduit in fluid communication with the first combined anode ejector fuel outlet and the first on-block fuel delivery flowpath fuel supply manifold.

[0043] The second off-block fuel flowpath may include a second anode ejector having a fuel supply inlet, a fuel return inlet, and a combined fuel outlet. The second off-block fuel flowpath may also include a second fuel supply conduit in fluid communication with the second anode ejector fuel supply inlet, a fuel source in fluid communication with the second fuel supply conduit, and a second fuel return conduit in fluid communication with the second anode ejector fuel return inlet and the first on-block fuel delivery flowpath fuel exhaust manifold. Further, the second off-block fuel flowpath may include a second combined fuel supply conduit in fluid communication with the second combined anode ejector fuel outlet and the second on-block fuel delivery flowpath fuel supply manifold.

[0044] In some examples, the first and second off-block fuel flow paths and the first and second on-block fuel feed flow paths are each configured to provide a recirculation ratio in the range of 7.5 to 15 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel feed inlet.

[0045] In some examples, the fuel cell system fuel cell block with a fuel cell stack having a first and a second segment includes an external auxiliary flowpath including an auxiliary ejector with an oxidant supply inlet, a fuel exhaust inlet, an oxidant exhaust inlet, a recirculation inlet, and an outlet. Further, the auxiliary flowpath may include an oxidant supply line (e.g., supply line) in fluid communication with the auxiliary ejector oxidant supply inlet and an oxidant source.Additionally, the auxiliary flowpath may include a fuel exhaust conduit in fluid communication with the auxiliary ejector fuel exhaust inlet and the first in-block fuel delivery flowpath fuel exhaust manifold, and an oxidizer exhaust conduit in fluid communication with the auxiliary ejector oxidizer exhaust inlet and the second in-block oxidizer flowpath oxidizer exhaust manifold. Additionally, the auxiliary flowpath may include an auxiliary exhaust conduit in fluid communication with the auxiliary ejector outlet; and a return conduit in fluid communication with the auxiliary ejector return inlet and the auxiliary exhaust conduit.

[0046] In some examples, a fuel cell system includes a fuel cell stack having a plurality of solid oxide fuel cells, each having an anode, a cathode, and an electrolyte. The fuel cell system may also include a fuel supply manifold, a fuel exhaust manifold, and one or more fuel delivery channels forming a flow path between the fuel supply and fuel exhaust manifolds. The one or more fuel delivery channels are in fluid communication with the anodes of the plurality of fuel cells. Further, the fuel cell system may include a fuel delivery system having a source of unreformed fuel and an ejector having an input of unreformed fuel from the fuel source, an input for recirculated fuel from the fuel exhaust manifold, and an output for combined fuels from the inputs, provided at the fuel supply manifold.Additionally or alternatively, the fuel cell system may be configured such that the recycle ratio of the recycled fuel mass to the unreformed fuel mass is in the range of 4.5:1 to 15:1. Additionally or alternatively, the fuel cell system may be configured such that the output of the combined fuels fed to the fuel supply manifold comprises at most 11 wt% methane. Additionally or alternatively, the fuel cell system may be configured such that the temperature of the fluid entering the fuel supply manifold is not greater than the temperature of the combined fuels output from the ejector. For example, the fuel cell system may not include a heat exchanger between the output of the ejector and the fuel supply manifold, which would otherwise add thermal energy (i.e., heat) to the fuel flowing into the fuel supply manifold.

[0047] Corresponding methods are further contemplated. In some examples, a fuel cell system includes a fuel cell stack configured for in-block reforming. The method includes receiving a fuel from a fuel source through a fuel supply manifold of the fuel cell stack. The method may further include receiving an oxidant from an oxidant source through an oxidant supply manifold of the fuel cell stack. The method may also include reforming the received fuel with the received oxidant by the fuel cell stack. In some examples, all of the fuel reforming of the fuel cell system is performed by the fuel cell stack (i.e., 100% in-block reforming).The method may also include: expelling fuel exhaust gas from the fuel cell stack through the fuel cell stack. Furthermore, the method may include: expelling cathode exhaust gas, e.g., oxidant, through an oxidant exhaust manifold of the fuel cell stack. Furthermore, the method may include: receiving fuel from the fuel source through an anode ejector, and receiving a first portion of the fuel exhaust gas from the fuel exhaust manifold through the anode ejector. Furthermore, the method may include: supplying a fuel stream comprising at least a portion of the received fuel and / or the received first portion of the fuel exhaust gas through the anode ejector.The method may further comprise removing higher hydrocarbons from a fuel stream from the anode ejector by a pre-reformer; and passing the fuel stream through the pre-reformer to the fuel supply manifold of the fuel cell stack for in-block reforming.

[0048] In another example, a method for providing fuel to the anodes of a solid oxide fuel cell stack comprises: withdrawing unreformed fuel from a fuel source; combining the unreformed fuel with at least a portion of the fuel exhausted from the fuel cell stack; pre-reforming the combined unreformed fuel and exhausted fuel; and reforming the unreformed fuel, the improvement comprising: reforming all of the unreformed fuel in the fuel cell stack.

[0049] In yet another example, a method in a fuel cell system comprises: expelling fuel exhaust gas through a fuel exhaust manifold of a fuel cell stack; expelling oxidant exhaust gas through an oxidant exhaust manifold of the fuel cell stack; receiving fuel from a fuel source through an anode ejector; receiving a first portion of the fuel exhaust gas from the fuel exhaust manifold through the anode ejector; supplying a fuel stream comprising at least a portion of the received fuel and / or the received first portion of the fuel exhaust gas to a pre-reformer through the anode ejector; removing higher hydrocarbons from the fuel stream from the anode ejector through the pre-reformer;the pre-reformer directing the fuel stream to a fuel supply manifold of the fuel cell stack for in-block reforming; the fuel cell stack receiving an oxidant from an oxidant source through an oxidant supply manifold; and the fuel cell stack in-block reforming the fuel stream with the received oxidant, wherein all fuel reforming of the fuel cell system is performed by the fuel cell stack.

[0050] In some examples, the anode ejector supplies a fuel stream including at least a portion of the received fuel and / or the received first portion of the fuel off-gas to a pre-reformer based on a recycle ratio range, e.g., a range of 7.5 to 15, of a mass of the first portion of the fuel off-gas from the fuel off-gas manifold to a mass of the fuel from the fuel source. In another example, the anode ejector supplies a fuel stream including at least a portion of the received fuel and / or the received first portion of the fuel off-gas to a pre-reformer, wherein a weight percentage of methane in the fuel stream supplied by the anode ejector is at most eleven percent. Other corresponding methods according to the disclosures are also contemplated herein.

[0051] Among other advantages, the disclosures provide fuel cell systems having fuel cell stacks configured for in-block reforming. The fuel cell systems include pre-reformers in which incoming fuel is pre-reformed to remove higher hydrocarbons, and the remainder of the fuel is reformed directly within the fuel cell stack without the need for an external reformer. In this way, the difference between the fuel cell stack (cathode) air temperature at the fuel cell stack outlet and the fuel cell stack inlet is significantly reduced. As a result, the temperature of the fuel entering the fuel cell stack inlet is increased. Additionally, the temperature of the fuel exiting the fuel cell stack is decreased, reducing exit degradation of the fuel cell stack.Another benefit is a more even current distribution throughout the fuel cell stack, resulting in a longer-lasting fuel cell stack. For example, the internal electrical resistance of the fuel cell varies with temperature. Thus, the amount of current a fuel cell can deliver varies with temperature. A more uniform temperature throughout the fuel cell stack would mean that all cells would have a narrower range of internal resistance and therefore produce a narrower range of currents. This is an advantage, at least because the fuel cell stack tends to degrade based on how much current is drawn. If some fuel cells degrade faster than others, the fuel cell stack may reach its end-of-life, although some cells may still be usable.This system also offers cost advantages, as no external reformer is required in the fuel cell system. Further advantages of the subject matter will become apparent to those skilled in the art from the disclosure, based on the claims, the accompanying drawings, and the following detailed description of the embodiments. Short description of the drawings Fig. 1 shows a fuel cell system according to some embodiments of the disclosure; Fig. 2 shows another fuel cell system according to some embodiments of the disclosure; Fig. 3 shows yet another fuel cell system according to some embodiments of the disclosure; and Fig. 4 shows another fuel cell system according to some embodiments of the disclosure. Further description

[0052] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are particularly described herein. The objects and advantages of the claimed subject matter will become more apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings. It is to be understood, however, that the disclosure is not intended to be limited to the specific forms disclosed. Rather, the disclosure is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.

[0053] Fig. 1 shows a fuel cell system 100 that includes a fuel cell stack 102, an oxidant source 108, a fuel source 110, an anode ejector 112 (also called a fuel ejector), a cathode ejector 114 (also called an oxidant ejector), a pre-reformer 144, and an auxiliary ejector 116. The system includes the IBR of fuel. For example, in some examples, all of the fuel reforming (i.e., 100%) occurs within the fuel cell stack 102. The IBR may include dry or wet reforming. The fuel cell system 100 may also include auxiliary equipment and components. In this example, the fuel cell system 100 includes a compressor 134, a turbine 136, a generator 138, and a recuperator 142.

[0054] The fuel cell stack 102 may include a plurality of individual fuel cells (not shown). The individual fuel cells may each include an anode, a cathode, and an electrolyte. The fuel cell stack 102 may also include a fuel supply manifold 120 (also known as a fuel inlet manifold) configured to receive a fuel stream from the pre-reformer 144.

[0055] Further, the fuel cell stack 102 may include a fuel exhaust manifold 118 configured to expel (e.g., degas) fuel exhaust, including unconsumed fuel (e.g., fuel that has been reformed (reformat)) and / or fuel cell reaction products, from the fuel cell stack 102. The fuel exhaust may be supplied to the intake of the anode ejector 112, the intake of the auxiliary ejector 116, or other auxiliary equipment such as an afterburner (not shown). The fuel exhaust manifold 118 may also be configured to expel fuel exhaust to the atmosphere, or may be configured to supply or expel the fuel exhaust using any combination of these options.

[0056] The anode ejector 112 may receive a source of fuel from the fuel source 110 and may further receive fuel off-gas from the fuel off-gas manifold 118 from the fuel cell stack 102, which is recirculated to the anode ejector 112 as previously mentioned. The anode ejector 112 is configured to supply the fuel to the pre-reformer 104. In some examples, the anode ejector 112 is configured to supply fuel based on a high recirculation ratio. For example, the anode ejector 112 may be configured to supply fuel based on a recirculation ratio in the range of 7.5 to 15. In some examples, the anode ejector 112 supplies fuel containing less than 11% methane to the pre-reformer based on the recirculation ratio for which it is configured.

[0057] The pre-reformer 144 may be disposed between the outlet of the anode ejector 112 and the fuel supply manifold 120. The pre-reformer 144 functions to remove higher hydrocarbons from the fuel stream from the outlet of the anode ejector 112 and any higher hydrocarbons that may be present in the fuel exhaust gas recycled to the anode ejector 112. The pre-reformer 144 may be an adiabatic catalytic converter capable of removing higher hydrocarbons without any heat input other than the heat from the fuel from the source 110 and that recycled from the fuel exhaust gas 118.

[0058] In some examples, the fuel source provides desulfurized natural gas to the anode ejector 112. Methane gas that may exit the anode ejector 112 is converted into syngas by steam reforming in the fuel cell stack 102. The resulting syngas is converted into carbon dioxide and water by the electrochemical process of the fuel cell stack 102.

[0059] The fuel cell stack 102 may further include an oxidant supply manifold 122 (which may be referred to as an oxidant inlet manifold) and an oxidant exhaust manifold 124. The oxidant supply manifold 122 is configured to receive an oxidant from the cathode ejector 114. Furthermore, the cathode ejector 114 is configured to receive oxidant exhausted from the oxidant exhaust manifold 124 of the fuel cell stack 102. Furthermore, the cathode ejector 114 is configured to deliver the received oxidant to the plurality of cathodes within the fuel cell stack 102.

[0060] The oxidizer exhaust manifold 124 may be configured to deliver the oxidant from the fuel cell stack 102 for delivery to the suction side of the cathode ejector 114, the suction side of the auxiliary ejector 116, and / or another component, such as an afterburner (not shown). Further, the oxidizer exhaust manifold 124 may be configured to vent the oxidant to the atmosphere, or may be configured to exhaust or vent the oxidant in a combination of these ways.

[0061] The oxidant exhaust supplied to the suction side of the cathode ejector 114 flows through a portion of a cathode loop. In this example, the cathode loop consists of the oxidant flow path from the cathode ejector 114 into the oxidant supply manifold 122, from which the oxidant is supplied to the cathodes in the fuel cell stack 102, exhausted from the oxidant exhaust manifold 124, and returned to the intake of the cathode ejector 114. As can be seen, the cathode loop is not a closed system, as oxidant can enter the loop from the oxidant supply 108 and exit the loop via the intake of the ejector 116. For example, in some embodiments, the cathode loop can be viewed as including the oxidant source 108 and the additional components illustrated between the oxidant source 108 and the fuel cell stack 102.Additionally, in some examples, the cathode loop may include an oxidant flow that is ionized and diffused through one or more fuel cell electrolytes of the fuel cell stack.

[0062] An afterburner (not shown), which may be integral with the auxiliary ejector 116, may be supplied with fresh oxidant, which may provide the energy used to feed the auxiliary ejector 116. The auxiliary ejector 116 may draw a portion of fuel exhaust from the fuel exhaust manifold 118, a portion of oxidant from the oxidizer exhaust manifold 124, and may further draw fuel gases produced by the auxiliary ejector 116.

[0063] In this example, a portion of the fuel cell system 100 includes an anode loop. The anode includes the fuel flow path from the pre-reformer 114 into the fuel inlet manifold 120, out of the fuel exhaust manifold 118, into the anode ejector 112, and back into the pre-reformer 144. The anode loop may also include the fuel flow path from the fuel source 110 into the anode ejector 112.

[0064] Fuel source 110 may be a fuel source, e.g., hydrocarbon fuel, desulfurized natural gas, or any other fuel type. Oxidant source 108 may include storage tanks filled with an oxidant, e.g., pure oxygen, atmospheric air, or other oxidant source, or a system configured to generate an oxidant supply.

[0065] As previously mentioned, fuel cell system 100 includes compressor 134, turbine 136, generator 138, and recuperator 142. Recuperator 142 may be supplied with oxidant from compressor 134 to a set of cold-side channels therein. Similarly, recuperator 142 may be supplied with exhaust from turbine 136 to a set of hot-side channels. Recuperator 142 is located upstream of cathode ejector 114 and auxiliary ejector 116 and functions to transfer heat between the exhaust from turbine 136 and the oxidant supplied by compressor 134.

[0066] The generator 138 may supply electrical power to the turbine 136. The turbine 136 drives the compressor 134 and the generator 138 and may receive the combustion products, for example, from the auxiliary ejector 116. The combustion products may expand as they pass through the turbine 136. The exhaust gas from the turbine 136 may be supplied to the recuperator 142 to effect heat transfer therein before being exhausted to the atmosphere. The turbine 136 may also be configured to vent the exhaust gas to the atmosphere.

[0067] Compressor 134 may be located downstream of oxidant supply 108. Compressor 134 may draw in and compress the oxidant used to drive cathode ejector 114 and auxiliary ejector 116. In this example, compressor 134 is configured to supply the compressed oxidant to recuperator 142.

[0068] In some embodiments, the fuel cell system 100 may be one of several integrated fuel cell systems. As shown on the right side of Fig. 1, the right arrow below the cathode ejector 114 labeled "To Additional Integrated Blocks" indicates that the oxidant may flow to another integrated fuel cell system to supply oxidant to that system's cathode ejector and auxiliary ejector. In such an embodiment, the compressor 134 may provide compressed oxidant to the multiple integrated fuel cell systems. Similarly, according to the arrow labeled "From Additional Integrated Blocks," the exhaust from the auxiliary ejector 116 may be supplied to a common exhaust manifold that discharges into the turbine 136. In some embodiments, multiple turbines and compressors may be used between the multiple integrated fuel cell systems.

[0069] Fig. 2 shows a fuel cell system 200 which includes similar components as those previously described with reference to Fig. 1. Similar to the fuel cell system 100 of Fig. 1, the system includes the IBR of fuel. For example, in some examples, all fuel reforming occurs in the fuel cell stack 102. However, in this example, the fuel cell stack 102 has two chambers, i.e., a first chamber 103 and a second chamber 104. Furthermore, the fuel cell system 200 includes two anode ejectors, including an anode ejector 112 and an anode ejector 113, and two pre-reformers, including a pre-reformer 144 and a pre-reformer 145.

[0070] The anode ejector 112 may receive a source of fuel from the fuel source 110 and may further receive fuel exhaust from the fuel exhaust manifold 118 from the chamber 104 of the fuel cell stack 102. The anode ejector 112 is configured to supply the fuel to the pre-reformer 144.

[0071] The pre-reformer 144 may be disposed between the outlet of the anode ejector 112 and the fuel supply manifold 120 of the chamber 103 of the fuel cell stack 102. The pre-reformer 144 functions to remove higher hydrocarbons from the fuel stream from the outlet of the anode ejector 112 and any higher hydrocarbons that may be present in the fuel exhaust gas recirculated to the anode ejector 112. The pre-reformer 144 supplies the fuel stream to the fuel supply manifold 120 of the chamber 103 of the fuel cell stack 102.

[0072] Similarly, the anode ejector 113 may receive a source of fuel from the fuel source 110 and may further receive fuel exhaust from a fuel exhaust manifold 128 from the chamber 103 of the fuel cell stack 102. The anode ejector 113 is configured to supply the fuel to the pre-reformer 145.

[0073] The pre-reformer 145 may be disposed between the outlet of the anode ejector 113 and the fuel supply manifold 130 of chamber 14 of the fuel cell stack 102. The pre-reformer 145 functions to remove higher hydrocarbons from the fuel stream from the outlet of the anode ejector 113 and any higher hydrocarbons that may be present in the fuel exhaust gas recirculated to the anode ejector 113. The pre-reformer 145 supplies the fuel stream to the fuel supply manifold 130 of chamber 104 of the fuel cell stack 102.

[0074] In some examples, fuel source 110 provides desulfurized natural gas to both anode ejector 112 and anode ejector 113. Any methane that may exit anode ejector 112 is converted to syngas in chamber 103 of fuel cell stack 102 through steam reforming. The resulting syngas is converted to carbon dioxide and water by the electrochemical process of fuel cell stack 102. Similarly, any methane that may exit anode ejector 113 is converted to syngas in chamber 104 of fuel cell stack 102 through steam reforming. The resulting syngas is converted to carbon dioxide and water by the electrochemical process of fuel cell stack 102.Thus, the use of two anode ejectors in this example enables fuel delivery to the fuel cell stack 102 with a lower methane concentration than in some systems that may use only one anode ejector. In some examples, the anode ejectors combine to deliver fuel with a methane concentration of 11% or less.

[0075] Fig. 3 shows a fuel cell system 300 which corresponds to the fuel cell system 200 of Fig. 2, but further includes a heat exchanger 306. In this example, the oxidant flows through cold side channels of the heat exchanger 306 before entering the oxidant supply manifold 122 of the fuel cell stack 102. In this example, the cathode ejector 114 is configured to receive fresh oxidant from the oxidant source 108 and supply the oxidant to the hot side channels of the heat exchanger 306.

[0076] A source of hot fluid is supplied to the hot-side channels of heat exchanger 306, e.g., in this example, the exhaust gas from auxiliary ejector 116. In other examples, another warm fluid may be used. For example, the warm fluid may be combustion products from an afterburner, which may be integrated with auxiliary ejector 116 and combusts a portion of fuel exhaust from the anodes of fuel cell stack 102, the oxidant exhaust from the cathodes of fuel cell stack 102, oxidant from compressor 134, or a combination of these fluids. After passing through the hot-side channels of heat exchanger 306, the warm fluid may be supplied to the suction side of auxiliary ejector 116, as in this example. In some examples, the warm fluid may be vented to the outside environment.

[0077] Fig. 4 illustrates a fuel cell system 400 similar to the fuel cell system 300 of Fig. 3. However, in this example, the heat exchanger 306 is located downstream and not upstream of the cathode ejector 114. Thus, in this example, the cold side channels of the heat exchanger 306 receive oxidant from the oxidant supply 108. After passing through the heat exchanger 306, the oxidant is fed to the cathode ejector 114. As in the fuel cell system 300 of Fig. 3, a source of hot fluid is supplied to the hot-side channels of heat exchanger 306, e.g., in this example, the exhaust gas from auxiliary ejector 116. After passing through the hot-side channels of heat exchanger 306, the warm fluid may be supplied to the suction side of auxiliary ejector 116 as in this example. In some examples, the warm fluid may be vented to the outside environment.

[0078] Among other advantages, the disclosures provide fuel cell systems having fuel cell stacks configured for in-block reforming. The fuel cell systems include pre-reformers in which incoming fuel is pre-reformed to remove higher hydrocarbons, and the remainder of the fuel is reformed directly within the fuel cell stack without the need for an external reformer. In this way, the difference between the fuel cell stack (cathode) air temperature at the fuel cell stack outlet and the fuel cell stack inlet is significantly reduced. As a result, the temperature of the fuel entering the fuel cell stack inlet is increased. Additionally, the temperature of the fuel exiting the fuel cell stack is decreased, reducing exit degradation of the fuel cell stack.Another advantage is a more even current distribution throughout the fuel cell stack, resulting in a longer-lasting fuel cell stack. This system also offers cost advantages, as no external reformer is required in the fuel cell system.

[0079] Further advantages of the subject matter will become apparent to those skilled in the art from the disclosure in light of the claims, the accompanying drawings and the following detailed description of the embodiments.

[0080] Although preferred embodiments of the subject matter have been described, it should be understood that the described embodiments are for illustrative purposes only and that the scope of the subject matter is to be determined only by the appended claims, with full equivalence accorded to them, and the numerous modifications and variations that will be apparent to those skilled in the art from their language.

Claims

[1] System that has: a fuel cell block comprising: a fuel cell stack (102) with several solid oxide fuel cells, wherein each solid oxide fuel cell comprises an anode, a cathode and an electrolyte; an in-block fuel feed flow path including a fuel supply manifold (120), a fuel exhaust manifold (118) and one or more fuel delivery channels in fluid communication with the fuel supply manifold (120) and the fuel exhaust manifold (118), each anode being exposed to a fuel flowing in one or more of the fuel delivery channels; and an in-block oxidizer flow path comprising an oxidizer supply manifold (122), an oxidizer exhaust manifold (124), and one or more oxidizer channels in fluid communication with the oxidizer supply manifold (122) and the oxidizer exhaust manifold (124), each cathode being exposed to an oxidizer contained in one or more flows through oxidation channels; an off-block oxidizer flow path comprising: a cathode ejector (114) with an oxidant supply inlet, an oxidizer return inlet and a combined oxidizer outlet; an oxidant supply line in fluid communication with the cathode ejector oxidant supply inlet; an oxidant source (108) in fluid communication with the oxidant supply line; an oxidizer return line in fluid communication with the cathode ejector oxidizer return inlet and the in-block oxidizer flowpath oxidizer exhaust manifold; and a combined oxidant supply line in fluid communication with the combined cathode ejector oxidant output and the in-block oxidizer flowpath oxidant supply manifold; and an off-block fuel flow path comprising: an anode ejector (112) having a fuel supply inlet, a fuel return inlet and a combined fuel outlet; a fuel supply line in fluid communication with the anode ejector fuel supply inlet; a fuel source (110) in fluid communication with the fuel supply line; a fuel return line in fluid communication with the anode ejector fuel return inlet and the in-block fuel feed flowpath fuel exhaust manifold; and a combined fuel supply conduit in fluid communication with the combined anode ejector fuel output and the in-block fuel delivery flowpath fuel supply manifold, wherein the out-of-block fuel flowpath and the in-block fuel delivery flowpath are configured to effect a recirculation ratio in the range of 4.5 to 15 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel delivery inlet. further comprising a pre-reformer (144) in a flow path formed by the combined fuel supply line of the block-external fuel flow path. [2] The system of claim 1, wherein the off-block fuel flow path and the on-block fuel delivery flow path are configured to provide a ratio in the range of 6 to 8 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel supply inlet. [3] The system of claim 2, wherein the off-block fuel flow path and the on-block fuel delivery flow path are configured to effect a ratio of about 7.5 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel supply inlet. [4] The system of claim 1, wherein the off-block fuel flow path and the on-block fuel delivery flow path are configured to cause a weight percentage of methane in a fluid flowing into the on-block fuel delivery flow path fuel supply manifold of no more than eleven percent. [5] The system of claim 1, wherein the pre-reformer (144) is an adiabatic catalytic converter configured to remove higher hydrocarbons from the fuel. [6] The system of claim 1, further comprising an off-block auxiliary flow path comprising: an auxiliary ejector (116) having an oxidant supply inlet, a fuel exhaust inlet, an oxidant exhaust inlet, a recirculation inlet, and an outlet; an oxidant supply line in fluid communication with the auxiliary ejector oxidant supply inlet and the oxidant source (108); a fuel exhaust line in fluid communication with the auxiliary ejector fuel exhaust inlet and the in-block fuel delivery flowpath fuel exhaust manifold; an oxidizer exhaust conduit in fluid communication with the auxiliary ejector oxidizer exhaust inlet and the in-block oxidizer flowpath oxidizer exhaust manifold; an auxiliary exhaust line in fluid communication with the auxiliary ejector outlet; and a return line in fluid communication with the auxiliary ejector return inlet and the auxiliary exhaust line. [7] The system of claim 6, further comprising an afterburner in a flow path formed by the auxiliary exhaust conduit. [8] The system of claim 7, further comprising a heat exchanger (306) for transferring thermal energy between a fluid output of the afterburner and a fluid flowing in the combined oxidant supply line. [9] The system of claim 7, further comprising a heat exchanger (306) for transferring thermal energy between a fluid output of the afterburner and a fluid flowing in the oxidant supply line. [10] System that has: a fuel cell block comprising: a fuel cell stack (102) having a first segment and a second segment, each segment having a plurality of solid oxide fuel cells, each solid oxide fuel cell having an anode, a cathode and has an electrolyte; a first in-block fuel delivery flow path comprising a first fuel supply manifold (120), a first fuel exhaust manifold (118), and one or more first fuel delivery channels in fluid communication with the first fuel supply manifold (120) and the first fuel exhaust manifold (118), each anode in the first segment being exposed to fuel flowing in one or more of the first fuel delivery channels; a second in-block fuel delivery flowpath comprising a second fuel supply manifold (130), a second fuel exhaust manifold (128), and one or more second fuel delivery channels in fluid communication with the second fuel supply manifold (130) and the second fuel exhaust manifold (128), each anode in the second segment being exposed to fuel flowing in one or more of the second fuel delivery channels; and an in-block oxidizer flow path comprising an oxidizer supply manifold (122), an oxidizer exhaust manifold (124), and one or more oxidizer channels in fluid communication with the oxidizer supply manifold (122) and the oxidizer exhaust manifold (124), each cathode in the first and second segments being exposed to an oxidizer disposed in flows through one or more oxidation channels; an off-block oxidizer flow path comprising: a cathode ejector (114) with an oxidant supply inlet, an oxidizer return inlet and a combined oxidizer outlet; an oxidant supply line in fluid communication with the cathode ejector oxidant supply inlet; an oxidant source (108) in fluid communication with the oxidant supply line; an oxidizer return line in fluid communication with the cathode ejector oxidizer return inlet and the in-block oxidizer flowpath oxidizer exhaust manifold; and a combined oxidant supply line in fluid communication with the combined cathode ejector oxidant output and the in-block oxidizer flow path oxidizer supply manifold; a first off-block fuel flow path comprising: a first anode ejector (112) having a fuel supply inlet, a fuel return inlet and a combined fuel outlet; a first fuel supply line in fluid communication with the first anode ejector fuel supply inlet; a fuel source (110) in fluid communication with the first fuel supply line; a first fuel return line in fluid communication with the first anode ejector fuel return inlet and the second in-block fuel delivery flowpath fuel exhaust manifold; and a first combined fuel supply line in fluid communication with the first combined anode ejector fuel outlet and the first in-block fuel delivery flowpath fuel supply manifold; and a second off-block fuel flow path comprising: a second anode ejector (113) with a fuel supply inlet, a fuel return inlet and a combined fuel outlet; a second fuel supply line in fluid communication with the second anode ejector fuel supply inlet; a fuel source (110) in fluid communication with the second fuel supply line; a second fuel return line in fluid communication with the second anode ejector fuel return inlet and the first in-block fuel delivery flowpath fuel exhaust manifold; and a second combined fuel supply conduit in fluid communication with the second combined anode ejector fuel output and the second in-block fuel delivery flowpath fuel supply manifold, wherein the first and second out-of-block fuel flowpaths and the first and second in-block fuel delivery flowpaths are each configured to provide a recirculation ratio in the range of 4.5 to 15 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel delivery inlet cause further comprising a pre-reformer (144) in a flow path formed by the second combined block-external fuel flow path fuel supply line. [11] The system of claim 10, wherein the first off-block fuel flow path and the second off-block fuel flow path and the first and second on-block fuel feed flow paths are configured to provide a recirculation ratio in the range of 6 to 8 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel feed inlet. [12] The system of claim 11, wherein the first off-block fuel flow path and the second off-block fuel flow path and the first and second on-block fuel feed flow paths are configured to provide a recirculation ratio of about 7.5 of a fuel mass flowing into the anode ejector fuel return inlet to a fuel mass flowing into the anode ejector fuel feed inlet. [13] The system of claim 10, wherein the first off-block fuel flow path and the second off-block fuel flow path and the first and second on-block fuel delivery flow paths are configured to cause a weight percentage of methane in a fluid flowing into the first on-block fuel delivery flow path fuel supply manifold and the second on-block fuel delivery flow path fuel supply manifold of no more than eleven percent. [14] The system of claim 10, wherein the pre-reformer (144) is an adiabatic catalytic converter configured to remove higher hydrocarbons from the fuel. [15] The system of claim 10, further comprising an off-block auxiliary flow path comprising: an auxiliary ejector (116) having an oxidant supply inlet, a fuel exhaust inlet, an oxidant exhaust inlet, a recirculation inlet, and an outlet; an oxidant supply line in fluid communication with the auxiliary ejector oxidant supply inlet and the oxidant source (108); a fuel exhaust conduit in fluid communication with the auxiliary ejector fuel exhaust inlet and the first in-block fuel delivery flowpath fuel exhaust manifold; an oxidizer exhaust conduit in fluid communication with the auxiliary ejector oxidizer exhaust inlet and the second in-block oxidizer flowpath oxidizer exhaust manifold; an auxiliary exhaust line in fluid communication with the auxiliary ejector outlet; and a return line in fluid communication with the auxiliary ejector return inlet and the auxiliary exhaust line. [16] The system of claim 15, further comprising an afterburner in a flow path formed by the auxiliary exhaust conduit. [17] The system of claim 16, further comprising a heat exchanger (306) for transferring thermal energy between a fluid output of the afterburner and a fluid flowing in the combined oxidant supply line. [18] The system of claim 16, further comprising a heat exchanger for transferring thermal energy between a fluid output of the afterburner and a fluid flowing in the oxidant supply line.

Images