Fuel cell system and method

Abstract

A fuel cell system, a method of at least partially cracking a fuel gas in a fuel cell system, and a method of starting a fuel cell system. The fuel cell system defines an anode inlet gas fluid flow path for delivering fuel gas from a first inlet of a recuperative heat exchanger to a first outlet of the recuperative heat exchanger, through a cracker, to a second inlet of the recuperative heat exchanger, through a first outlet of the recuperative heat exchanger, through a second outlet of the recuperative heat exchanger. The fuel cells are delivered to a second outlet of the recuperative heat exchanger and to an anode inlet of at least one fuel cell stack. The fuel cell system has a heat source configured to provide heat to the anode inlet gas fluid flow path between the first outlet of the regenerative heat exchanger and the second inlet of the regenerative heat exchanger. The recuperative heat exchanger is arranged to transfer heat from the at least partially cracked fuel gas at a relatively higher temperature from the cracker outlet to a fuel gas at a relatively lower temperature delivered between the first inlet and the first outlet of the recuperative heat exchanger.

Description

Technical Field

[0001] The present invention relates to improved fuel cell systems and methods. Background Art

[0002] Fuel cell systems (including fuel cells, fuel cell stacks, fuel cell stack assemblies, and heat exchanger systems), arrangements, and methods are well known to those of ordinary skill in the art. See, for example, WO2015 / 004419, which is incorporated herein by reference in its entirety.

[0003] Generally, fuel cells use hydrocarbons (such as natural gas) as fuel. In the case of solid oxide fuel cell (SOFC) systems where the fuel cell stack operates in the range of 400 - 650 °C (intermediate temperature solid oxide fuel cell or IT - SOFC) or more particularly in the temperature range of 520 - 620 °C (still IT - SOFC), it is necessary to partially reform the fuel in a reformer before the fuel enters the fuel cell because the temperature in the SOFC is not high enough for effective internal reforming of the fuel in the SOFC. For this purpose, a steam reformer is used in front of the fuel inlet of the fuel cell stack.

[0004] In some cases, it is desirable to avoid using a steam reformer.

[0005] It is also desirable to use other fuels (such as ammonia (NH3)) to operate fuel cells, especially ammonia as a by - product of other industrial processes, and there are fuel cell systems that use ammonia as fuel. See, for example, US2014 / 0072889 and WO2016 / 114214. However, for many forms of fuel cells where the electrochemically active layer of the fuel cell is coated, deposited, or mounted on a metal substrate (usually steel), particularly metal - supported solid oxide fuel cells, or in fuel cell systems where other components of the fuel cell (including connection bolts or welds) are made of metal (such as steel) or the electrolyte material is reactive with ammonia or may otherwise deteriorate (e.g., materials containing nickel (Ni)) when exposed to ammonia, introducing ammonia into the stack, especially at the operating temperatures possible for those systems, will cause problems. For steel, this may be attributed to metal nitridation, which may lead to failure of the relevant metal - containing components. Summary of the Invention

[0006] The present invention aims to provide a fuel cell system in which a reformer is not required and other fuels (such as ammonia) can be used more safely as fuel.

[0007] According to a first aspect of the present invention, there is provided a fuel cell system comprising:

[0008] (i) At least one fuel cell stack, which includes at least one fuel cell and has an anode inlet, a cathode inlet, an anode exhaust outlet, and a cathode exhaust outlet;

[0009] (ii) A cracker for cracking fuel gas into at least partially cracked fuel gas and having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas;

[0010] (iii) A regenerative heat exchanger; and

[0011] (iv) A heat source;

[0012] Wherein:

[0013] (a) The system defines an anode inlet gas fluid flow path for delivering fuel gas from a first inlet of the regenerative heat exchanger to a first outlet of the regenerative heat exchanger, through the cracker, to a second inlet of the regenerative heat exchanger, delivering to a second outlet of the regenerative heat exchanger and delivering to the anode inlet of the at least one fuel cell stack;

[0014] (b) The heat source is configured to provide heat to the anode inlet gas fluid flow path between the first outlet of the regenerative heat exchanger and the second inlet of the regenerative heat exchanger; and

[0015] (c) The regenerative heat exchanger is arranged to transfer heat from the relatively high-temperature at least partially cracked fuel gas from the cracker outlet to the relatively low-temperature fuel gas delivered between the first inlet and the first outlet of the regenerative heat exchanger, so as to increase the temperature of the fuel gas delivered between the first inlet and the first outlet of the regenerative heat exchanger for delivery to the cracker inlet, while reducing the temperature of the at least partially cracked fuel gas from the cracker between the second inlet and the second outlet of the regenerative heat exchanger for delivery to the anode inlet.

[0016] The regenerative heat exchanger has a separate flow path for each fluid, that is, for the cracked fuel gas (i.e., preferably thermal decomposition in the presence of a suitable catalyst to reduce the temperature at which cracking / decomposition occurs) and the relatively high-temperature at least partially cracked fuel gas from the cracker, and these fluids flow through the heat exchanger simultaneously during use, and heat exchange occurs on the walls of the separate flow paths, heating the former fluid and cooling the latter fluid.

[0017] In the case of the present invention, the fuel gas may be an ammonia-containing fuel gas. In this case, the ammonia can be cracked before it enters the fuel cell stack via the anodic inlet gas fluid flow path (i.e., the first fluid flow path), thereby reducing or eliminating nitridation within the fuel cell stack, and in particular nitridation of its metal components (such as the metal substrate of a metal-supported solid oxide fuel cell, or the separator or interconnect plate, or the pipes or manifolds within the fuel cell stack), or the interaction of other reactive or incompatible materials with ammonia.

[0018] Alternatively, the fuel gas may be a methanol-containing fuel gas. In this case, the methanol can be cracked before it enters the fuel cell stack via the anodic inlet gas fluid flow path (i.e., the first fluid flow path), thereby reducing or eliminating coking caused by methanol decomposition within the fuel cell stack, and in particular coking in its fluid channels (such as within the cell unit (e.g., on the metal substrate, separator or interconnect plate of a metal-supported solid oxide fuel cell) or the pipes or manifolds within the fuel cell stack). If such coking is not reduced or eliminated, it may reduce the efficiency of the fuel cell stack (and the system therein) by at least partially blocking the anodic inlet gas fluid flow path (i.e., the first fluid flow path).

[0019] It should be understood that for similar reasons as already described with respect to ammonia and methanol, the present invention can also be used for other fuel gases, such as methane and higher hydrocarbons, as well as ethanol and higher alcohols.

[0020] Furthermore, since a regenerative heat exchanger is provided in addition to the cracker, the efficiency of the fuel cell system can be increased because the heat of the heat source can be used in a cyclic manner. It a) heats the fuel gas in the cracker to achieve the purpose of effectively maintaining an efficient cracking process for the fed (e.g., ammonia-containing or methanol-containing) fuel gas (cracking is an endothermic reaction, so cracking requires a heat source to maintain the operating temperature), and b) heats the products of such an endothermic reaction, i.e., the at least partially cracked fuel gas (usually during the reaction, but often also after the reaction, i.e., while still in the cracker), when heating the anodic inlet gas fluid flow path extending through the cracker, so that the reaction products can be used via the regenerative heat exchanger to preheat the fuel gas before it enters the cracker. This increases the efficiency of the cracker by avoiding waste of heat, and it also increases the service life of the cracker by reducing the heat load on the cracker (by preheating the feed).

[0021] This recuperation operation then pre - conditions the reaction product (i.e., at least partially cracked fuel gas from the cracker) before it enters the fuel cell stack by cooling it with the source fuel gas in a recuperative heat exchanger. This is also beneficial because without cooling, at least partially cracked fuel gas from the cracker is typically too hot for the fuel cell stack, and the arrangement of the present invention allows the cooling process to occur simultaneously with the pre - heating process for the source fuel gas, thus avoiding, minimizing, or reducing system heat losses and additional thermal gradients within system components. After all, fuel cell stacks typically operate effectively within a given temperature range, and the temperature is usually lower than the temperature at which efficient cracking of the fuel gas (e.g., ammonia) is optimally achieved, especially in the case of IT - SOFCs, where the optimal stack temperature may be up to 620 °C, while the required ammonia cracking temperature may be approximately 700 °C.

[0022] The heat source can be configured to directly supply heat to the anode inlet gas fluid flow path, or the heat source can be configured to indirectly supply such heat to the anode inlet gas fluid flow path.

[0023] In some embodiments, the fuel gas is an ammonia - containing fuel gas. In some embodiments, the ammonia in the ammonia - containing fuel gas can be a by - product of other industrial processes.

[0024] In some embodiments, the fuel gas is a methanol - containing fuel gas.

[0025] In some embodiments, the cracker has a catalyst for cracking the fuel gas, the catalyst is disposed on one side of the second heat exchanger, and the catalyst forms part of the anode inlet gas fluid flow path.

[0026] In some embodiments, the recuperative heat exchanger is a counter - current heat exchanger.

[0027] In some embodiments, the cracker is arranged to supply or transfer heat from a heat source (preferably an internal heat source disposed within the fuel cell system boundary and typically via a heated fluid from the heat source (e.g., via a second fluid flow path configured to convey the heated fluid)) to the anode inlet gas fluid flow path to provide energy for cracking. In some embodiments, the heat source is a tail gas incinerator of the fuel cell system, i.e., an internal tail gas incinerator, or a catalytic combustor of the fuel cell system, or the heat source can be an external furnace or a direct - insertion electric heater.

[0028] In some embodiments, heat is provided by a second heat exchanger, which is preferably an integral part of the cracker, whereby the cracker includes the second heat exchanger. However, other forms of crackers are also known, and the heat exchanger for transferring heat to the fuel gas can be separate from the cracker. In some embodiments, for example, the second heat exchanger is between the fuel heat recuperator and the cracker for transferring heat to the recuperation loop upstream of the fuel heat recuperator. Then the cracker does not need to include a heat exchanger.

[0029] In some embodiments, the fuel cell system further includes a second gas fluid flow path, a heat source is configured to provide heat to the second gas fluid flow path, and wherein the fuel cell system is arranged to transfer heat from the second gas fluid flow path to the anode inlet gas fluid flow path (the first gas fluid flow path) to provide energy for cracking. The fuel cell system also preheats the fuel gas before cracking to bring the fuel gas up to the temperature for cracking.

[0030] In some embodiments, the second heat exchanger is a countercurrent heat exchanger, for example having parallel flows in opposite directions. A countercurrent heat exchanger means that the fuel gas in the anode inlet gas fluid flow path reaches the highest available temperature at the outlet of the heat exchanger, thus providing the maximum available energy to facilitate cracking.

[0031] In some embodiments, the second gas fluid flow path includes an exhaust gas fluid flow path from the anode exhaust gas outlet and the cathode exhaust gas outlet of the stack to the heat source and to the cracker. The exhaust gas passing through this second gas fluid flow path is the gas that has been heated by passing through the stack (at the operating temperature T), so the temperature of the exhaust gas leaving the stack approximately corresponds to the operating temperature T, and then the heat source further heats those gases to a temperature more suitable for the outlet temperature of the cracker. This thus improves the cracking performance (since the temperature of the cracker can be optimized) and uses the operating temperature T of the stack to avoid the need for higher energy from the heat source (since the exhaust gas has been preheated by the stack).

[0032] In some embodiments, the second gas fluid flow path extends from the cracker to the exhaust outlet of the fuel cell system. Generally, the second gas fluid flow path passes through a third heat exchanger, for example for heating the oxidant at the cathode inlet. This is after providing heat to the anode inlet gas fluid flow path (i.e., the first fluid flow path) via the cracker.

[0033] It should be understood that the cracker operates as a heat exchanger or particularly includes a heat exchanger that is arranged to transfer heat from the second gas fluid flow path to the anode inlet gas fluid flow path to provide energy for cracking the fuel gas.

[0034] In some embodiments, the heat source is disposed upstream of the cracker (within the fuel cell system) in the second gas fluid flow path. In some embodiments, the heat source is the tail gas burner of the fuel cell system. In other embodiments, the heat source is the catalytic burner of the fuel cell system. In some embodiments, the cracker is a catalytic combustion cracker, such as a catalytic combustion cracker having an integrated catalytic combustion catalyst. The catalyst can be part of the second heat exchanger or downstream thereof.

[0035] In some embodiments, the second heat exchanger (the internal heat exchanger of the cracker) includes a countercurrent heat exchanger.

[0036] In some embodiments, the cracker has a catalyst for cracking the fuel gas (e.g., a catalyst for cracking ammonia in an ammonia-containing fuel gas or a catalyst for cracking methanol in a methanol-containing fuel gas), the catalyst is disposed on one side of the second heat exchanger, typically on the first side, and the catalyst forms part of the anode inlet gas fluid flow path. Thus, the catalyst is on the side of the heat exchanger configured to receive the fuel gas (or in the flow path of the heat exchanger).

[0037] In some embodiments, the system is configured to use the exhaust gases from the anode exhaust gas outlet and the cathode exhaust gas outlet when the heat source is provided.

[0038] In some embodiments, the heat source is a tail gas burner (TGB) configured to burn the exhaust gases from the anode exhaust gas outlet and the cathode exhaust gas outlet, wherein the exhaust gas fluid flow path is configured to direct the combusted exhaust gas to the cracker (for passing through the heat exchanger of the cracker). Since the combusted exhaust gas has a relatively high temperature compared to the fuel gas, the cracker is configured to transfer heat from the relatively high temperature combusted exhaust gas to the relatively low temperature fuel gas.

[0039] In some embodiments, the heat source is a catalytic combustion cracker heat exchanger (CCCHX) configured to catalytically combust the exhaust gases from the anode exhaust gas outlet and the cathode exhaust gas outlet, the CCCHX has a catalyst for cracking the fuel gas (e.g., ammonia-containing or methanol-containing) coated on the anode inlet gas fluid flow path of the CCCHX, and has a catalyst for catalytically combusting the exhaust gases from the anode exhaust gas outlet and the cathode exhaust gas outlet on the exhaust gas fluid flow path of the CCCHX, and the catalytic combustion is configured to provide the heat source for cracking the fuel gas (e.g., ammonia in an ammonia-containing fuel gas or methanol in a methanol-containing fuel gas).

[0040] In some embodiments, a supplementary pipeline is provided, which is configured to supply fuel gas (preferably ammonia-containing fuel gas or methanol-containing fuel gas) and / or oxidant to a heat source (e.g., an exhaust gas incinerator, a catalytic combustor, or a CCCHX). The supplementary pipeline is typically configured to supply the same fuel gas to the heat source as that at the inlet of the regenerative heat exchanger or the cracker inlet.

[0041] In some embodiments, the fuel cell system includes control software, which is configured to use the supplementary fuel gas to increase the temperature of the exhaust gas fluid flow path downstream of the heat source.

[0042] In some embodiments, the exhaust gas fluid flow path further includes an oxidant heat exchanger, which is located between the cracker and the exhaust port of the exhaust gas fluid flow path. The oxidant heat exchanger is configured to supply heat from the exhaust gas fluid flow path to the oxidant, and the oxidant is configured to be supplied to the cathode inlet.

[0043] In some embodiments, the oxidant is configured to be supplied to the cathode inlet via an oxidant fluid flow path from an oxidant source to the cathode inlet.

[0044] In some embodiments, the system is provided with a bypass around the oxidant heat exchanger, such that the exhaust gas fluid flow path can selectively bypass the oxidant heat exchanger.

[0045] In some embodiments, the anode inlet gas fluid flow path further includes a pipeline from the regenerative heat exchanger to the anode inlet, and the pipeline is configured for heat exchange between the at least partially cracked fuel gas and one or both of at least one fuel cell stack and a heat source. This can be heat transferred from the stack to the at least partially cracked fuel gas, or vice versa.

[0046] The pipeline can be wound around the stack or the heat source (e.g., an exhaust gas incinerator).

[0047] In some embodiments, at least a portion of the at least partially cracked fuel gas from the second outlet of the regenerative heat exchanger is fed through another heat exchanger before entering the stack as fuel for the stack. The another heat exchanger can further condition the fuel before it is fed to the stack. Typically this is to heat the fuel, but if the regenerative heat exchanger does not cool the gas to or below the required stack feed temperature, it can instead be arranged to reduce its temperature.

[0048] Such another heat exchanger can advantageously be a recuperative heat exchanger rather than a countercurrent heat exchanger, because the heat exchanger is generally intended to equalize the temperatures between two fluids rather than maximize the heat transfer from one fluid to another.

[0049] In some embodiments, another heat exchanger is thermally connected to the fuel cell stack, whereby the fuel cell stack provides heating for the fuel passing through the other heat exchanger.

[0050] In a set-up situation, another heat exchanger can alternatively (or instead) be arranged to effect heat exchange between the at least partially cracked fuel gas and the oxidant just before entering the anode inlet and the cathode inlet of the fuel cell stack. An additional air bypass can be provided to connect the air / oxidant supply to the said other heat exchanger.

[0051] In the case of the present invention, a tail gas incinerator or a catalytic combustor is a useful device provided as a heat source. However, the heat source does not necessarily have to be a tail gas incinerator or a catalytic combustor integrated into the fuel cell system. For example, the heat source can be an external heat source, or even an electric heater for feeding heat to the anode inlet gas fluid flow path. However, since a fuel cell system usually has a tail gas incinerator or a catalytic combustor, it is preferred to provide at least one of them as the heat source (or as part of the heat source).

[0052] In some embodiments, the present invention further includes a source of ammonia-containing fuel gas, such as an ammonia-containing fuel gas tank. In such cases, the cracker has a catalyst for cracking ammonia, which is provided on one side of the second heat exchanger, and this catalyst forms part of the anode inlet gas fluid flow path.

[0053] In some embodiments, an ammonia supply is provided. The ammonia supply can be ammonia of at least 95% purity or a lower purity mixture of ammonia and other gases, and especially in cases where the other gases are mainly nitrogen and hydrogen. For example, the ammonia supply can be partially cracked ammonia.

[0054] In some embodiments, the present invention further includes a source of methanol-containing fuel gas, such as a methanol-containing fuel gas tank. In such cases, the cracker has a catalyst for cracking methanol, which is provided on one side of the second heat exchanger, and such a catalyst forms part of the anode inlet gas fluid flow path.

[0055] In some embodiments, a methanol supply is provided. The methanol supply can be methanol of at least 95% purity or a lower purity mixture of methanol and other gases, and especially in cases where the other gases are mainly nitrogen and hydrogen. For example, the methanol supply can be partially cracked methanol.

[0056] In some embodiments, the fuel cell system is a medium-temperature or high-temperature fuel cell system.

[0057] In some embodiments, the fuel cell system is a medium-temperature fuel cell system, and the operating temperature of its fuel cell stack is between 400°C and 700°C, especially 450 - 650°C, and more especially 520 - 620°C.

[0058] In the case of the present invention, there are generally three heat exchange stages: heat exchange from the heat source to the fuel gas (for cracking); heat exchange with the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger by at least a portion of the cracked fuel gas at the relatively high temperature from the cracker outlet; and heat exchange for cooling at least a portion of the cracked fuel gas at the relatively high temperature by the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger.

[0059] In some embodiments, the fuel gas fed to the first inlet of the regenerative heat exchanger is provided at a temperature below 60 °C, and more typically at room temperature (about 20 °C), or at a temperature below room temperature (if sourced from a compressed gas supply such as a gas cylinder), due to thermal cooling during expansion before entering the regenerative heat exchanger.

[0060] In some embodiments, the fuel cell system includes a metal-supported fuel cell, the electrochemically active layer of which is coated, deposited or mounted on a metal support or plate. Typically, a plurality of such fuel cells are stacked to form a stack, as described for example in WO2015 / 004419.

[0061] In some embodiments, the fuel cell system includes a solid oxide fuel cell, i.e., the electrochemically active region is a solid oxide. With different electrochemically active electrolyte chemistries, there are many possible SOFC configurations. For example, three well-known electrolyte materials are yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), and gadolinium-doped ceria (GDC or CGO). Desirably, it is a mid-temperature solid oxide fuel cell or IT-SOFC, the stack operating temperature of which is between 400 °C and 700 °C. However, in some embodiments, the fuel cell system includes a high-temperature fuel cell, the stack operating temperature of which is between 750 °C and 1100 °C.

[0062] In some embodiments, flame combustion is used to provide the heat source. Typically, the flame combustion occurs in the tail gas incinerator of the fuel cell system, which is connected, for example, to the anode exhaust outlet and the cathode exhaust outlet of the fuel cell stack.

[0063] In some embodiments, catalytic combustion is used to provide the heat source. Typically, the catalytic combustion occurs in the catalytic combustor of the fuel cell system, which is connected, for example, to the anode exhaust outlet and the cathode exhaust outlet of the fuel cell stack.

[0064] In some embodiments, the heat source and the cracker are separate units of the fuel cell system, connected by a piping system. For example, the heat source may include a hot gas output port, and the cracker may include a hot gas input port fluidly connected to the hot gas output port of the heat source.

[0065] In some embodiments, the heat source and the cracker are combined into a single integrated unit.

[0066] In some embodiments, the heat source and the cracker are combined as a catalytic combustion-cracker heat exchanger (CCCHX).

[0067] In some embodiments, a bypass or variable valve providing flow control is provided between the heat source and the cracker for bypassing or reducing / changing the heat flow from the heat source to the cracker. For example, a bypass from the heat source can be provided to allow at least a portion of the heat from the heat source to be diverted for alternative operations, or to completely bypass heating the anode inlet gas fluid flow path within the cracker. Alternatively, the flow rate from the heat source can be controlled to reduce the heat transfer rate. The bypass or flow rate can be controlled by a controller to maintain the desired temperature of the output of at least a portion of the cracked fuel gas from the cracker outlet. For example, if the temperature of the cracker output is to be increased, then all (or a larger proportion) of the flow from the heat source can be passed through to the cracker, but if the temperature of the cracker output is to be decreased, then some or all of the flow from the heat source can be diverted or slowed down.

[0068] In some embodiments, the bypass allows some of the heat from the heat source to be used elsewhere in the system, or to be used by other nearby equipment, especially equipment where the required heat output is higher than the effluent flowing out of the cracker.

[0069] In some embodiments, when in the steady operating state of the cracker, it is intended that the cracker operates between 550 °C and 900 °C, preferably between 650 °C and 900 °C, more preferably between 650 °C and 750 °C, and most likely at about 700 °C. However, in some embodiments, when in the steady operating state of the cracker, the cracker operates between 550 °C and 600 °C.

[0070] In some embodiments, the fuel gas is an ammonia-containing fuel gas, and the goal of cracking the ammonia-containing fuel gas is to have less than 1000 parts per million of ammonia in the fuel fed to the stack. It has been shown that an operating temperature of 700 °C or higher easily achieves this goal. In the case of some crackers, 700 °C is equivalent to 231 ppm at the output. Some such catalysts preferably operate at 650 - 700 °C and still ensure that it will achieve <1000 ppm at the required fuel flow rate of the stack.

[0071] These temperatures are the peak temperatures of the fuel gas within the cracker.

[0072] Typically, 700 °C is higher than the operating temperature of the stack in an intermediate fuel cell system (e.g., a metal-supported solid oxide fuel cell system), but this heat source is selected to provide the desired temperature within the cracker, such as between 650 °C and 750 °C, or preferably above 700 °C. However, in some embodiments, when in a steady operating state of the cracker, it operates between 550 °C and 600 °C.

[0073] In some embodiments, the fuel gas is a methanol-containing fuel gas, and the goal of cracking the methanol-containing fuel gas is to have less than 1000 parts per million of methanol in the fuel fed to the stack. An operating temperature at or above 700 °C has been shown to readily achieve this goal. Some catalysts preferably operate at 300 - 400 °C and still ensure that it will achieve <1000 ppm at the desired fuel flow rate of the stack. Thus, the methanol-containing fuel gas (and its cracking) is particularly advantageous for a PEM fuel cell stack / system. The operating temperature of such a PEM fuel cell stack / system is lower than the required temperature for methanol cracking, but the heat source can still supply the heat required for cracking.

[0074] In some embodiments, the fuel cell system has an anode exhaust gas recirculation path configured to recirculate a portion of the anode exhaust gas from the anode exhaust gas outlet of at least one fuel cell stack to the anode inlet of at least one fuel cell stack. This can increase the overall system efficiency.

[0075] In some embodiments, the anode exhaust gas recirculation path includes a getter configured to remove un-cracked fuel gas from the anode exhaust gas recirculation path. This reduces the proportion of un-cracked fuel gas directed to the anode inlet of at least one fuel cell stack and can increase the overall system efficiency.

[0076] According to another embodiment of the present invention, there is provided a fuel cell system comprising:

[0077] (i) at least one fuel cell stack including at least one fuel cell and having an anode inlet, a cathode inlet, an anode exhaust gas outlet, and a cathode exhaust gas outlet;

[0078] (ii) a cracker for cracking a fuel gas into at least partially cracked fuel gas and having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas;

[0079] (iii) a regenerative heat exchanger; and

[0080] (iv) a heat source;

[0081] Wherein:

[0082] (a) The system defines an anode inlet gas fluid flow path for delivering fuel gas from a first inlet of the regenerative heat exchanger to a first outlet of the regenerative heat exchanger, through the cracker, to a second inlet of the regenerative heat exchanger, to a second outlet of the regenerative heat exchanger and to the anode inlet of the at least one fuel cell stack;

[0083] (b) The heat source is configured to provide heat to the anode inlet gas fluid flow path between the first outlet of the regenerative heat exchanger and the second inlet of the regenerative heat exchanger; and

[0084] c) A bypass or variable valve providing flow control is provided between the heat source and the cracker for bypassing or reducing / changing the heat flow from the heat source to the cracker.

[0085] In some embodiments, the bypass allows at least a portion of the heat to be diverted from the cracker for alternative use.

[0086] Such a system can also be based on the foregoing system.

[0087] The present invention also provides a method for at least partially cracking a fuel gas, which includes: providing a system as defined above; flowing the fuel gas through the anode inlet gas fluid flow path; and providing heat to the anode inlet gas fluid flow path via a heat source between a first outlet of the regenerative heat exchanger and a second inlet of the regenerative heat exchanger.

[0088] In the case of the present invention, at the start of cracking, the method at least partially cracks the fuel gas in the cracker. In a preferred embodiment, this is achieved while delivering heat from the heat source through the cracker, but the heat can also instead be provided to the fuel gas outside the cracker (e.g., ammonia-containing). Providing heat to the anode inlet gas fluid flow path can be direct or indirect.

[0089] In some embodiments, the operating temperature of the cracker is between 550 °C and 900 °C, preferably between 650 °C and 900 °C, and more preferably between 650 °C and 750 °C, and most likely around 700 °C. This operating temperature is particularly suitable for ammonia-containing fuel gas and is the peak temperature to which the ammonia-containing fuel gas in the cracker rises during normal operation. Those skilled in the art will understand that during the warm-up period, the cracker will initially be exposed to room temperature and start warming up from this temperature during the warm-up cycle.

[0090] In some embodiments where the fuel gas is an ammonia-containing fuel gas, at least a portion of the at least partially cracked fuel gas leaving the cracker contains less than 1000 parts per million of ammonia.

[0091] In some embodiments where the fuel gas is a methanol-containing fuel gas, the cracker can have the operating temperature as described above, but it may be advantageous for its operating temperature to be between 250 °C and 450 °C, preferably between 300 °C and 400 °C. In such cases, it can preferably be used in a PEM fuel cell system. In such cases, at least a portion of the cracked fuel gas leaving the cracker may contain less than 1000 parts per million of methanol.

[0092] In some embodiments, the heat source is configured to combust the exhaust gases from the anode exhaust gas outlet and the cathode exhaust gas outlet, and the exhaust gas fluid flow path is configured to direct the combusted exhaust gases to the cracker at a relatively high temperature compared to the fuel gas, and the cracker is configured to transfer heat from the relatively high-temperature combusted exhaust gases to the relatively low-temperature fuel gas.

[0093] In some embodiments, there are three heat exchange stages: heat exchange from the heat source to the fuel gas; heat exchange through at least a portion of the relatively high-temperature cracked fuel gas from the cracker outlet with the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger; and heat exchange for cooling at least a portion of the relatively high-temperature cracked fuel gas through the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger.

[0094] In some embodiments, the fuel gas fed to the first inlet of the regenerative heat exchanger is provided at a temperature below 60 °C, and more typically at room temperature (about 20 °C), or at a temperature below room temperature (if sourced from a compressed gas supply such as a gas cylinder, due to thermal cooling during expansion before entering the regenerative heat exchanger).

[0095] In some embodiments, the target for the ammonia in the fuel gas to be cracked, which is the fuel to be fed to the stack, is for example less than 1000 parts per million. It has been shown that an operating temperature of 700 °C or higher achieves this target. Tests have shown that in some cases of the cracker, at equilibrium, 525 °C can achieve ≤ 1000 ppm, and above this temperature, lower ppm are achieved at the cracker outlet. In some cases of the cracker, 700 °C is equivalent to 231 ppm at the output. However, typical catalysts preferably operate at 650 - 700 °C to ensure that it will achieve < 1000 ppm at the required fuel flow rate of the stack.

[0096] These temperatures are the peak temperatures of the fuel gas within the cracker.

[0097] Typically, 700 °C is higher than the operating temperature of the stack, but this heat source is selected to provide the required temperature within the cracker, such as between 650 °C and 750 °C, or preferably above 700 °C. However, in some embodiments, when in a steady operating state of the cracker, it operates between 550 °C and 600 °C.

[0098] The present invention also provides a method for starting the fuel cell system as described above, which includes:

[0099] Supplying an oxidant and a supplementary fuel to a heat source to generate a heat exhaust gas;

[0100] Using the heat from the heat exhaust gas, providing heat via an oxidant heat exchanger to preheat the oxidant for feeding into the cathode inlet of the stack; and

[0101] Once a predetermined portion of the stack reaches a first threshold temperature, start the flow of fuel gas through the anode inlet gas fluid flow path (or increase the rate of said flow).

[0102] The present invention also provides a method for starting a fuel cell system, the fuel cell system including:

[0103] At least one fuel cell stack having an oxidant inlet and a fuel inlet,

[0104] An oxidant heat exchanger for an oxidant flow reaching the oxidant inlet of the stack, a heat source for heating the at least one fuel cell stack, and

[0105] A cracker for cracking a fuel gas into at least a partially cracked fuel gas, the cracker having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas for feeding into the fuel inlet of the stack,

[0106] The method includes:

[0107] Heating the at least one fuel cell stack to a first threshold temperature; and

[0108] Once the at least one fuel cell stack reaches the first threshold temperature, start the flow of the fuel gas to the cracker or increase the rate of said flow.

[0109] A heat source (or a different heat source, e.g., in the case where more than one heat source is provided) can heat the cracker and / or the fuel gas.

[0110] The method may include:

[0111] Supplying an oxidant and a supplementary fuel to (or a different) heat source to generate a heat exhaust gas;

[0112] Using heat from the hot exhaust gas, provide heat via the oxidant heat exchanger to preheat the oxidant for feeding into the oxidant inlet of the fuel cell stack; and

[0113] Once a predetermined part of the fuel cell system reaches a first threshold temperature, start the flow of fuel gas to the cracker (or increase the rate of said flow).

[0114] The present invention also provides a method for starting a fuel cell system, the fuel cell system comprising:

[0115] At least one fuel cell stack having an oxidant inlet and a fuel inlet,

[0116] An oxidant heat exchanger for an oxidant stream reaching the oxidant inlet of the stack, a heat source, and

[0117] A cracker for cracking fuel gas into at least partially cracked fuel gas, the cracker having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas for feeding into the fuel inlet of the stack,

[0118] The method comprises:

[0119] Providing an oxidant and a supplementary fuel to the heat source to generate hot exhaust gas;

[0120] Using heat from the hot exhaust gas, provide heat via the oxidant heat exchanger to preheat the oxidant for feeding into the oxidant inlet of the stack; and

[0121] Once a predetermined part of the fuel cell system reaches a first threshold temperature, start the flow of fuel gas to the cracker (or increase the rate of said flow).

[0122] In each method, the fuel cell system is preferably as defined above.

[0123] In some embodiments, the predetermined part is part of the stack. In another embodiment, it can be part of the cracker.

[0124] In some embodiments, the oxidant is provided to the heat source via an oxidant fluid flow path, the oxidant from an oxidant source to the oxidant inlet or cathode inlet of the stack, through the stack and out of the cathode exhaust gas outlet of the stack to reach the heat source.

[0125] In some embodiments, the heat source is a tail gas incinerator or a catalytic combustor connected to the anode exhaust gas outlet and the cathode exhaust gas outlet of the stack.

[0126] In some embodiments, the predetermined portion is at a location in the exhaust gas fluid flow path between the anode exhaust outlet or the cathode exhaust outlet of the stack and the oxidant heat exchanger. The exhaust gas fluid flow path typically passes through the cracker, but in some embodiments, the exhaust gas fluid flow path can selectively bypass it.

[0127] In some embodiments, the predetermined portion is part of the cracker, such as the cracker outlet of the cracker. The first threshold temperature can be a temperature that is at or between 700 °C and 800 °C. The fuel gas stream that then begins flowing into the fuel cell system anode inlet gas fluid flow path can be effectively cracked in the cracker and then penetrate into the stack.

[0128] In some embodiments, after the flow of fuel gas to the cracker is initiated, the method includes gradually increasing the flow rate of the fuel gas to the cracker.

[0129] In some embodiments, after the flow of fuel gas to the cracker is initiated, the method includes reducing the flow rate of the supplementary fuel. In some embodiments, the reduction of the supplementary fuel rate can be initiated simultaneously with the start of the flow of fuel gas, but there can alternatively be a delay between them.

[0130] In some embodiments, the method includes controlling the gradual increase in the fuel flow rate and / or the gradual decrease in the supplementary fuel flow rate so that a predetermined portion of the fuel cell system remains at or above the first threshold temperature. In other embodiments, the method includes controlling the gradual increase in the fuel flow rate and / or the gradual decrease in the supplementary fuel flow rate so that a predetermined location in the exhaust gas fluid flow path remains at or above a predetermined temperature. Preferably, the temperature is at or between 700 °C and 800 °C. In some embodiments, the predetermined location is alternatively or additionally a location in or on the fuel thermal recuperator of the fuel cell system, such as the temperature of at least partially cracked fuel before or at the second inlet of the regenerative heat exchanger. The temperature at this location may need to be maintained at T > 500 °C.

[0131] In some embodiments, the first threshold temperature is the inlet temperature of the fuel cell and it can be between 400 °C and 500 °C, or more preferably at about 450 °C (e.g., for the fuel, or the oxidant, or both).

[0132] Accordingly, the present invention also provides for warming up the system from room temperature / ambient temperature by supplementally flowing fuel through a heat source, typically an exhaust gas burner or a catalytic burner.

[0133] In the case of the present invention, there can be multiple heating-up periods. For example, starting from a cold start, there is an initial preheating using an oxidant and a supplementary fuel. Then, when at a first given predetermined temperature, for example when the air inlet or outlet temperature of the fuel cell stack reaches 450 °C, the method can include slowly introducing fuel through the cracker and the stack to enter a fuel-assisted heating-up period.

[0134] Then an air temperature at the inlet or outlet of the stack of approximately 450 - 500 °C allows starting to draw current from the stack. Then this becomes a current-assisted heating-up period.

[0135] Then, when the temperature at the air outlet of the fuel cell stack reaches approximately 600 °C, this can be used to indicate that the fuel cell system has transitioned to a substantially steady-state operating point. BRIEF DESCRIPTION OF THE DRAWINGS

[0136] The present invention will now be described in further detail, by way of example only, with reference to the accompanying drawings, in which:

[0137] Figure 1 There is schematically shown a first fuel cell system according to the present invention, which has an air preheater, a fuel heat recuperator and an ammonia cracker, using a tail gas incinerator as the heat source for the ammonia cracker;

[0138] Figure 2 There is schematically shown Figure 1 A modified version of the fuel cell system, which has a bypass or variable valve providing flow control between the heat source and the ammonia cracker for bypassing or reducing / changing the heat flow from the heat source to the cracker;

[0139] Figure 3 There is schematically shown Figure 1 Another modified version of the fuel cell system, which incorporates an alternative configuration for supplying fuel to its fuel cell stack, having a fuel heater (or heat exchanger) for supplying heat to the oxidant of the stack and the fuel of the stack (or exchanging heat between the oxidant of the stack and the fuel of the stack);

[0140] Figure 4 There is schematically shown an alternative fuel cell system according to the present invention, in which a combined catalytic combustion cracker is used instead of Figure 1 A separate tail gas incinerator and ammonia cracker;

[0141] Figure 5 There is schematically shown for application to Figure 4 The embodiment of Figure 3 Modifications;

[0142] Figure 6Shows a diagram schematically representing an example of the fluid temperature of ammonia / cracked ammonia when fed to and passing through an ammonia cracker, from its first penetration into the fuel heat recuperator, through the ammonia cracker and again through the fuel heat recuperator, and then through the stack;

[0143] Figure 7 and Figure 8 Schematically shows the relative working fluid temperatures of the fluid passing through the recuperative heat exchanger and the countercurrent heat exchanger respectively;

[0144] Figure 9 Schematically shows a typical fuel cell, and a plurality of such fuel cells can be stacked into a fuel cell stack;

[0145] Figure 10 Schematically provides a graphical representation of the variation with time of various inputs and outputs (such as fluid flow rate, temperature and current) reaching or from the fuel cell system of the present invention during system startup or during a warm-up cycle;

[0146] Figure 11 Schematically shows Figure 1 An optional modified configuration of the fuel cell system during system startup or warm-up cycle; and

[0147] Figure 12 Schematically shows Figure 3 A modified configuration of the fuel cell system. Detailed Description

[0148] First referring to Figure 1 , schematically shows a fuel cell system 100 according to the present invention. The fuel cell system 100 is illustrated by reference to an ammonia-containing fuel gas. The fuel cell system 100 includes a fuel cell stack 10, a heat source 12, an air preheater 14, a fuel heat recuperator 16, an ammonia cracker 18, and a fuel temperature pre-regulator 20. In this embodiment, the heat source 12 is an exhaust gas incinerator 12, which is connected to the stack 10, and the fuel temperature pre-regulator 20 is a heat exchanger 20, which can be in the form of a pipe wound around the stack or some other hot or cold object, depending on whether the fluid passing through the stack 10 is to be heated or cooled.

[0149] The fuel cell stack 10 includes at least one fuel cell 82, for example Figure 9 as shown, and has an oxidant (usually cathode) inlet 28, a fuel (usually anode) inlet 30, an oxidant (usually cathode) exhaust gas outlet 48, and a fuel (usually anode) exhaust gas outlet 46. The fuel cell or each fuel cell 82 is formed by a cathode layer 84, an anode layer 86, and an electrochemically active layer 88, and can be as described, for example, in WO2015 / 004419.

[0150] AsFigure 9 As shown, during the operation of the fuel cell system 100, an oxidant (usually air 22) enters the fuel cell / stack 10, 82 at the oxidant inlet 28, fuel enters the fuel cell / stack 10, 82 at the fuel inlet 30, the cathode exhaust gas leaves the fuel cell / stack 10, 82 at the oxidant exhaust outlet 48, and the anode exhaust gas leaves the fuel cell / stack 10, 82 at the anode exhaust outlet 46, and a DC charge can be obtained from the fuel cell / stack 10, 82 at the terminals 90 at both ends (here the top and bottom) of the stack 10. Such operating characteristics of the fuel cell / stack are well known in the art.

[0151] Figure 1 The heat source 12 in is the tail gas incinerator 12. It receives the anode exhaust gas and the cathode exhaust gas from the fuel cell / stack 10, 82 and burns them together in a flame to generate a heat output. This heat output (usually hot exhaust gas) is discharged from the tail gas incinerator 12 through the heat outlet 36 of the tail gas incinerator 12.

[0152] Then, the heat output (hot exhaust gas) is transferred to the cracker 18 to provide heat for the cracker 18 at the heat input 38 of the cracker 18.

[0153] The cracker 18 is used to crack the ammonia-containing fuel gas. This gas is delivered here from the ammonia source 26, and the ammonia source can be from an adjacent separate process equipment that produces ammonia, a storage tank of ammonia, or an ammonia supply pipeline.

[0154] The ammonia-containing fuel gas is delivered to the cracker 18 at the cracker inlet 42 of the cracker 18, and after being processed by the cracker 18, it exits the cracker 18 at the cracker outlet 44 of the cracker 18 as at least partially cracked fuel gas.

[0155] The at least partially cracked fuel gas is fed from the cracker outlet 44 to the regenerative heat exchanger 16 at the fuel regenerative heat inlet 50 of the regenerative heat exchanger 16. Since the at least partially cracked fuel gas is still hot when it leaves the cracker 18, its heat can be used by the regenerative heat exchanger 16 to preheat the ammonia-containing fuel gas before the ammonia-containing fuel gas enters the cracker, that is, the regenerative heat exchanger 16 is downstream of the cracker 18. The regenerative heat exchanger 16 is also located upstream of the cracker 18, and the ammonia-containing fuel gas first enters the regenerative heat exchanger 16 at the fuel source inlet 52 of the regenerative heat exchanger 16, and then is heated by the heat of the at least partially cracked fuel gas in the regenerative heat exchanger 16, and then leaves the regenerative heat exchanger 16 at the preheated ammonia outlet 56 of the regenerative heat exchanger 16. The now preheated ammonia-containing fuel gas can then penetrate into the cracker 18 via the cracker inlet 42 as described above.

[0156] The at least partially cracked and partially cooled fuel gas can then leave the regenerative heat exchanger 16 via the fuel outlet 54 of the regenerative heat exchanger 16 to pass to the fuel inlet 30 of the fuel cell stack 10.

[0157] In this embodiment, before the at least partially cracked and partially cooled fuel gas enters the fuel cell stack, the fuel gas passes through a fuel temperature pre-regulator 20, which, as described above, is a heat exchanger 20 in this embodiment, preferably in the form of a pipe wound around the fuel cell stack or some other hot object, such that the at least partially cracked and partially cooled fuel gas can be pre-regulated to the correct temperature for entering the fuel cell stack, typically being heated by the heat of the fuel cell stack in the fuel temperature pre-regulator 20, but in some embodiments this may instead require further cooling, for example using a radiator or guiding the pipe near a cooler component to achieve additional heat loss.

[0158] The flow path of ammonia to the fuel inlet 30 before and after cracking is the first gas fluid flow path, also known as the anode inlet gas fluid flow path, which connects the fuel heat recuperator 16, the cracker 18, again the fuel heat recuperator 16, the fuel temperature pre-regulator 20 and the fuel cell stack 10 for delivering the ammonia-containing fuel gas from the first inlet 52 of the regenerative heat exchanger 16 to the first outlet 56 of the regenerative heat exchanger 16, through the cracker 18, to the second inlet 50 of the regenerative heat exchanger 16, to the second outlet 54 of the regenerative heat exchanger 16 and to the anode inlet 30 of at least one fuel cell stack 10. Further, the heat source 12 is configured to supply heat to the anode inlet gas fluid flow path in the cracker 18, thus providing heat between the first outlet 56 of the regenerative heat exchanger 16 and the second inlet 50 of the regenerative heat exchanger 16.

[0159] According to the present invention, the regenerative heat exchanger is arranged to transfer heat from the relatively high temperature at least partially cracked fuel gas from the cracker outlet 44 to the relatively low temperature ammonia-containing fuel gas delivered between the first inlet 52 and the first outlet 56 of the regenerative heat exchanger 16 from the ammonia source 26, so as to increase the temperature of the ammonia-containing fuel gas delivered to the regenerative heat exchanger 16 (such temperature increase occurs on the ammonia-containing fuel gas between the first inlet 52 and the first outlet 56 of the regenerative heat exchanger 16), ready for delivery to the cracker inlet 42, while reducing the temperature of the at least partially cracked fuel gas from the cracker 18 (between the second inlet 50 and the second outlet 54 of the regenerative heat exchanger 16) for subsequent delivery to the anode inlet 30 of the fuel cell stack 10.

[0160] In this embodiment, after using some of the heat of the hot exhaust gas, the cracker 18 discharges the hot exhaust gas via the hot outlet 40 of the cracker 18 so as to be subsequently used by the air preheater 14 of the fuel cell system 100, and then the hot exhaust gas leaves the system 100 at the exhaust port 24. This fluid flow path is the second gas fluid flow path.

[0161] The air preheater 14 is provided to preheat the oxidant (e.g., air or oxygen) of the stack 10. By preheating the air from the air source 22 and feeding the air through the air preheater, the stack is exposed to a smaller thermal shock. Similarly, by preheating the ammonia-containing fuel gas, the cracker 18 is exposed to a smaller thermal shock. The efficiency of the system can also be improved by using the exhaust gas of the stack to provide heat to the cracker, and this heat can also provide air preheating and ammonia-containing fuel gas preheating. In addition, the stack can also provide a certain degree of fuel preheating or preconditioning for the stack at the fuel temperature pre-regulator 20.

[0162] As Figure 1 shown, the oxidant (e.g., air or oxygen) from the air source enters the air preheater at the oxidant inlet 60 of the air preheater 14 and leaves the air preheater 14 at the air outlet 64 of the air preheater 14. Instead, the hot exhaust gas enters the air preheater 14 at the hot inlet 62 of the air preheater 14 and leaves the air preheater at the exhaust port 66 of the air preheater, and is guided by the exhaust port 66 to be discharged from the system 100 via the exhaust port 24. When the air and the hot exhaust gas are in the air preheater, the heat exchanger of the air preheater promotes the heat exchange between the exhaust gas and the air. Heat is transferred from the exhaust gas to the air, so that the exhaust gas is cooled and the air entering the stack is heated.

[0163] An air bypass 92 can be provided to allow air (or oxidant or oxygen) to bypass the air preheater, and control valves 68, 70 can be provided to allow automatic control of the bypass. Therefore, the temperature of the air mixture fed to the stack 10 can be controlled by mixing the hotter air from the air preheater with the cooler air from the source, so as to supply the stack 10 with air at the correct / desired temperature (or within the desired temperature range) as required. In some embodiments, the control valve 70 is provided upstream and downstream of the air preheater. In other embodiments, the control valve 70 is only provided upstream of the air preheater, and the mixer 68 is provided downstream of it, or vice versa.

[0164] As Figure 1As shown, the system 100 can additionally be provided with a fuel supplement 74 for the tail gas incinerator 12 such that if additional heat is required, additional fuel (or fuel and oxidizer, using separate respective supplement pipelines) can be delivered to the tail gas incinerator 12, for example, via one or more supplement inlets 58 into the tail gas incinerator 12. Such a supplement can be air from the air source 22 (e.g., via the stack or via a bypass), or air or oxidizer from elsewhere, and / or fuel from the ammonia source 26 or fuel from elsewhere.

[0165] The piping system connects the various schematically shown elements of such a system 100, as schematically shown by the connecting pipelines in the figure, but the specific configuration of the piping system can be routed differently because the specific positioning of the components between the installation facilities may vary.

[0166] Next, referring to Figure 2 , schematically shows Figure 1 a modified version of the system. In this alternative configuration, a bypass for the cracker 18 is provided such that the hot exhaust gas from the tail gas incinerator 12 can be redirected away from the cracker 18 and can optionally be directed to another device 78 that may require heat. In this embodiment, the bypass uses a variable valve 80 to allow the feed volume or feed rate ratio of the hot exhaust gas between the cracker 18 and the other device 78 to be controlled, but it could alternatively be a fixed valve (or more simply a fixed flow pipeline).

[0167] Next, referring to Figure 3 , schematically shows Figure 1 another modified version of the fuel cell system 100. It employs an alternative configuration for supplying its fuel to its fuel cell stack 10, still having a fuel temperature pre-regulator 20, but this time in the form of a fuel heater 20 rather than a pipe / heat exchanger around the stack 10. Additionally, in this embodiment, the fuel heater 20 additionally provides heat to the fuel for the stack 10 (at least partially cracked ammonia from the cracker 18, via the fuel heat recuperator) and (from) the oxidizer (or air or oxygen) for the stack 10 (or exchanges heat between the fuel for the stack 10 and the oxidizer for the stack 10). For this purpose, the fuel heater has a fuel inlet 94, a fuel outlet 96, an oxidizer inlet 98, and an oxidizer outlet 102. The fuel heater can be a heat exchanger for allowing heating before the oxidizer and / or fuel enters the stack 10. The fuel heater can be a recuperative heat exchanger that exchanges heat between the fuel (at least partially cracked ammonia from the cracker 18) and the oxidizer to ensure that the temperatures of the fuel and oxidizer at the fuel outlet 96 and the oxidizer outlet 102 (and thus also at the respective stack inlets) are similar, which reduces the thermal gradient and associated stress in the stack.

[0168] In this embodiment, an air bypass 92 is again provided to bypass the air preheater, as before, but a second air bypass 104 is additionally provided to bypass both the air preheater 14 and the fuel heater 20. Using suitable control valves for each of these air bypasses, the temperature of the air entering the fuel cell stack 10 and the temperature of the fuel entering the fuel cell stack 10 can each be independently controlled because the temperature of the air entering the fuel heater can be controlled. Thus, with respect to the heat exchanger in the fuel heater 20, the output temperatures of the two fluids from the fuel heater 20 can also be controlled (increased or decreased). For example, in one embodiment, the heat exchangers in the fuel heater can operate in a countercurrent manner, whereby the outlet temperatures of the heat exchangers will be coupled, i.e., substantially the same, and thus not independently controlled. However, at the fuel cell stack inlet, control can be restored via the bypass 104, which allows for a reduction or increase in the oxidant at the oxidant inlet of the fuel cell stack by adding (or not adding) an additional oxidant stream (the stream from the heat exchanger and the stream through the bypass) to the oxidant inlet. Since the temperature of the oxidant passing through the bypass will be lower than the temperature of the oxidant at the outlet of the oxidant from the heat exchanger, this can be used to offset or control the oxidant mixed stream at the oxidant inlet of the fuel cell stack, thus providing a controllable oxidant stream temperature at the oxidant inlet of the fuel cell stack.

[0169] Next, referring to the embodiment represented by Figure 4 the fuel cell system 100 is modified by replacing the separate cracker 18 and the tail gas incinerator 12 with a combined catalytic combustion cracker 106. Instead of the tail gas incinerator, a cracker and a separate catalytic burner can be provided, but by combining the two, space can be saved. Figure 1

[0170] In this embodiment, instead of flame combustion, the exhaust gas from the fuel cell stack 10 is catalytically combusted, thereby generating heat, and the cracker uses the heat to provide energy for the cracking of ammonia in the cracker (an endothermic process, so heat is required to maintain its operation). Excess heat is still generated (the hot exhaust gas from the combined catalytic combustion cracker 106), and thus this system can still be used to heat the air at the air preheater 14, as shown. Additionally, as Figure 5 shown, modifications can also be made to place a fuel heater 20 corresponding to Figure 3 to replace Figure 4 the pipeline as a fuel temperature pre-regulator 20, so that heating or heat exchange is again performed between the air and the fuel of the fuel cell stack 10. In Figure 5In order to simplify the drawings, the cracker and the fuel thermal recuperator (which respectively feed fluids into the air preheater 14 and the fuel heater 20) are not shown. However, the output from the cracker (ExhCrkOut), which enters the air preheater 14, is schematically shown; the output from the fuel thermal recuperator (FuelFhrOut), which enters the stack (STK) 10, is schematically shown; and the air input (AirFcmIn) for the fuel cell, which enters the air preheater 14, is schematically shown.

[0171] Next, referring to Figure 6 , a graphical representation of the sample temperature of ammonia / cracked ammonia as it is fed into and passes through the ammonia crackers 18, 106 is shown, starting from its first penetration into the fuel thermal recuperator 16, through the ammonia crackers 18, 106, and again through the fuel thermal recuperator 16, and then into the stack 10. This figure represents the cold side of the fuel thermal recuperator (left side), which represents the first pass of the fuel through the fuel thermal recuperator (FHR 16), in this case the fuel thermal recuperator (FHR 16) is used to prevent damage to the cracker (CRK 18) by increasing the fuel input temperature into the cracker, thus reducing the thermal gradient across the cracker; the central or intermediate "cracking" period, in this case the fuel temperature further increases (as it passes through the cracker 18) and finally reaches its peak temperature; and the hot side of the fuel thermal recuperator (right side), which represents the second pass of the fuel through the fuel thermal recuperator, reducing the temperature of the (now cracked) fuel to approach the "stack temperature".

[0172] More specifically, in the cold side, the ammonia from the fuel source 26 typically starts at room temperature / ambient temperature (about 20 °C). Since the fuel thermal recuperator is preferably of the cross-flow type, when the fuel first passes through the fuel thermal recuperator 16, its temperature increases at a relatively steady rate, as explained below with reference to Figure 8 .

[0173] Then when the fluid passes through the crackers 18, 106, the rate of temperature increase starts to gradually increase. Although the cracking process is endothermic, the temperature rises slowly due to the heat supplied by the tail gas burner / catalytic combustion. However, as the parts per million (ppm) of ammonia decreases, the effect of the endothermic reaction becomes smaller, and thus the cracking activity also decreases. Therefore, the cracked fuel then starts to heat up faster.

[0174] To maximize the thermal supply effect on the gas at the start of the cracking process and to better counteract the endothermic effect of the cracking process in the crackers 18, 106, a person skilled in the art might initially think that they need the crackers 18, 106 to operate as recuperative heat exchangers in the system. However, in the case where the temperature of the exhaust gas from the heat source is not high enough to be above the target operating temperature at which the crackers achieve the required degree of ammonia cracking (e.g., for achieving <1000 ppm ammonia, 700 °C), a counterflow heat exchanger becomes preferred. In terms of using the exhaust gas from the stack 10 as a heat source in the IT - SOFC, with the operating temperature of the stack typically being 600 °C, the heat source temperature is likely not high enough to be above the target cracking temperature. Thus, in a preferred aspect of the present invention, the crackers 18, 106 are made of counterflow heat exchangers instead of recuperative heat exchangers. In other words, using a counterflow heat exchanger maximizes the highest temperature on the fuel side of the heat exchanger, thus facilitating maximizing the proportion of ammonia cracked in the crackers 18, 106.

[0175] Then, the fluid (now at least partially cracked ammonia fuel) leaves the crackers 18, 106 and returns to the other side of the fuel heat recuperator 16 to steadily decrease in temperature as it heats the incoming ammonia. As shown, in this example, the ammonia gas fed into the crackers peaks at 700 °C because at this temperature, the ammonia crackers 18, 106 can achieve the target of less than 1000 ppm ammonia in the output gas stream (i.e., for the at least partially cracked ammonia fuel leaving the cracker 18). When the fluid re - leaves the fuel heat recuperator 16, it drops to around 300 °C as its heat is transferred to the source gas. Due to the temperature drop, the fluid needs to be reheated again before entering the stack 10. For example, for a medium - temperature solid oxide fuel cell system (e.g., a metal - supported solid oxide fuel cell system), it is reheated to a target temperature of around 450 °C. For this purpose, a fuel heater or fuel temperature pre - regulator 20 is used, which is preferably a recuperative heat exchanger to more or less equalize the temperature of the corresponding flow passing through it.

[0176] It should be understood that the above temperatures are provided only as examples. Different temperatures, higher or lower, can also be used. For example, the actual temperatures can vary depending on the size or efficiency of the corresponding heat exchanger, the specificity of the catalyst used for cracking (and thus the required temperature), and the relative flow rate / heat transfer rate of the system fluids and components.

[0177] Next, referring to Figure 7 and Figure 8 , the relative working fluid temperatures of the fluid passing through a recuperative heat exchanger and a counterflow heat exchanger are schematically shown, respectively.

[0178] In a recuperative heat exchanger, as Figure 7As shown, the temperatures of the two fluids start to increase / decrease rapidly, but as their temperatures approach each other (i.e., equilibrate), the rate of temperature change decreases. This characteristic makes the co-current heat exchanger potentially more suitable for an ammonia cracker because it can better counteract the peak endothermic effect at the start of the cracking process and thus when a high degree of cracking occurs. However, the compromise of using a co-current heat exchanger is that an intermediate temperature of the two fluids is ultimately achieved, and thus a large amount of heat from a heat source is required to achieve this. For example, for the ammonia gas product at the outlet of cracker 18, a temperature of 700 °C is desired (as in the present invention, the goal is a low parts per million of ammonia in the fluid leaving the cracker). Since the exhaust gas burner or catalytic combustion of the exhaust gas using the stack 10 may barely provide such a consistently high temperature (and especially without the need for supplementary fuel / oxidant, but supplementary fuel / oxidant can be provided when needed), the present inventors have realized that this co-current arrangement is not as suitable in practice as a counter-current arrangement.

[0179] Figure 8 A counter-current arrangement and the temperature characteristics of the fluids in such a heat exchanger are shown. As shown, this instead shows a generally linear rate of temperature change, and the heat exchange between the two fluids results in the temperature of the first fluid leaving the heat exchanger being similar to the temperature of the second fluid entering the heat exchanger (an approximation under certain assumptions, such as when the two fluids have similar properties other than temperature). This is beneficial for preheating the ammonia before it enters cracker 18, 106 because the ammonia can then be fed into the cracker at a high temperature (e.g., 500 °C) due to heat exchange between the at least partially cracked ammonia and the original ammonia input (at the fuel heat recuperator 16). It should be noted that this is beneficial because an ammonia cracker or generally a heat exchanger may have a shorter working life when exposed to high levels of thermal stress (e.g., when the feed temperature of the ammonia is very different from the feed temperature of the heat source). It also allows the heat from the exhaust gas burner or catalytic burner to be used as a heat source because the heat source does not need to be significantly hotter than the target cracker temperature.

[0180] Therefore, the present invention preferably uses a counter-current heat exchanger in cracker 18.

[0181] Next, referring to Figure 10 , a graphical representation of the variation over time of various exemplary inputs and outputs (such as fluid flow rate, temperature, and current) of the fuel cell system 100 of the present invention during system startup or during a warm-up cycle is schematically shown.

[0182] From Figure 10As can be seen, at t = 0, there is no air flow 108, the fuel cell stack air inlet temperature 110 is at its minimum value, there is no fuel cell stack current 112, the fuel cell stack fuel flow rate 114 (fuel flow rate to the fuel cell stack) is zero, the temperature at the cracker outlet (tExhCrkOut) 118 is at its minimum value, and the fuel cell stack air outlet temperature 120 is at its minimum value.

[0183] Starting from t = 0, the fuel cell stack is heated using a heater (an electric heater, or burning a hydrocarbon fuel at the burner, in a manner known to those skilled in the art and which can be a tail gas burner 12 or a catalytic burner 106), and an oxidant or air flows through the system 100, allowing the heater to provide the heat flowing through the system, heating the cracker 18 and the fuel cell stack 10, as indicated by the increase in the temperature at the cracker outlet (tExhCrkOut) 118 and the fuel cell stack air inlet temperature 110 and the fuel cell stack air outlet temperature 120. In fact, initially, the air flow and fuel flow increase sharply, and then the air flow reaches a steady state and this steady state is maintained even when the fuel cell system 100 reaches its full operating temperature.

[0184] Meanwhile, fuel can be started to be fed to the fuel cell stack 10, as indicated by the increase in the fuel cell stack fuel flow rate 114, which increase is caused by feeding ammonia through the fuel heat recuperator 16 to the fuel cell stack 18. This produces an initial change in the cracker outlet temperature 118 and a reactive flow rate change in the fuel cell stack fuel supply 114. At the same time, the fuel cell stack air outlet temperature continues to increase. Once around 500 °C is reached, for an IT-SOFC, when the electrochemical active layer 88 of the fuel cells 82 in the fuel cell stack 10 reaches the operating temperature, current 112 can be started to be drawn. Depending on the form / chemistry of the fuel cell, other temperatures can be applied instead. At the same time, the fuel flow rate to the fuel cell stack can reach a steady state. The fuel cell stack air inlet temperature 110 and the cracker outlet temperature 118 can also stabilize, but as shown, due to changes in the electrical load on the fuel cell stack, these temperatures may still change over an extended period.

[0185] During this warm-up / start-up cycle, it is preferred to slowly warm up the cracker to avoid excessive thermal shock to its components. In Figure 10 the example, the rate of increase in the temperature of the cracker 18 is limited, for example, by increasing / decreasing the air flow through the fuel cell stack 10, or using the bypass 92 of the air preheater 14, or by an additional bypass line 122 that also bypasses the fuel cell stack 10 and the tail gas burner 12, such that the outlet temperature 118 of the cracker increases at a rate similar to that of the fuel cell stack 10. For example, in some embodiments, it increases by no more than, for example, 25 °C per minute.

[0186] Next, referring to Figure 11 , schematically showsFigure 1 A modified configuration of the fuel cell system 100 during system startup or warm-up cycle, in which an additional bypass line 122 is shown. It can be seen that the system 100 still has the air preheater 14, the fuel cell stack 10, the tail gas burner 12, the fuel heat reheater 16 and the cracker 18. It also has a bypass 92 for selectively bypassing the air preheater 14. However, there is an additional bypass line 122, which is used to allow air to pass from the air source 22 directly into the effluent from the tail gas burner. Since the typical temperature of the air from the air source is 20-25°C, and the exhaust gas temperature of the tail gas burner is typically about 750°C, the temperature of the gas fed into the cracker hot inlet 38 can be reduced. Further control can also be performed using the variable valve 80 described previously, which can divert some of the gas flow from the tail gas burner (or heater) away from the cracker along the cracker bypass line 124, as previously described with respect to Figure 2 The variable valve 80 may provide thermal bypass for the air upstream of the insertion point of the additional bypass line 122, as shown, because this is more effective than positioning the variable valve thereafter by avoiding some of the effects of heat on the additional air.

[0187] Next reference Figure 12 , schematically showing Figure 3 A modified configuration of a fuel cell system in which an exemplary anode exhaust gas recirculation path 202 is provided. The anode exhaust gas recirculation path 202 is configured to recirculate a portion of the exhaust gas from the anode exhaust gas outlet of the stack 10 to the anode inlet of the stack 10. The exhaust gas from the anode exhaust gas outlet of the stack 10 may contain unused cracked fuel gas, which can be recirculated in the anode exhaust gas recirculation path 202 for use by the stack 10.

[0188] exist Figure 12 In the example of , the anode exhaust gas recirculation path 202 joins the anode inlet gas fluid flow path at the mixer 214 between the (outlet of) the recuperator heat exchanger (fuel heat regenerator 16) and the (inlet of) the air preheater 14. A portion of the exhaust gas from the anode exhaust gas outlet of the stack 10 is directed to the anode exhaust gas recirculation path 202 at the splitter 204. The splitter 204 can direct a fixed or variable (i.e., controlled) portion of the anode exhaust gas to the anode exhaust gas recirculation path 202, and the remainder is provided to the heat source 12 (tail gas incinerator 12), as described above.

[0189] like Figure 12As shown, the anode exhaust gas recirculation path 202 may also sequentially include an anode exhaust gas condenser heat exchanger 206, a pump 210, and a getter 212. The anode exhaust gas condenser heat exchanger 206 is configured to cool the anode exhaust gas in the anode exhaust gas recirculation path 202 by heat transfer using air or an oxidant 22. The anode exhaust gas condenser heat exchanger 206 is positioned upstream of the air preheater 14 in the air inlet fluid flow path. The bypass paths 92 and / or 104 may also bypass the anode exhaust gas condenser heat exchanger 206. The anode exhaust gas condenser heat exchanger 206 is configured to condense water 208 from the anode exhaust gas, and this water may be used elsewhere in the system or diverted out of the system. The pump 210 is configured to pump the anode exhaust gas around the anode exhaust gas recirculation path 202. The getter 212 is configured to remove ammonia from the anode exhaust gas in the anode exhaust gas recirculation path 202. In this way, the proportion of ammonia in the anode exhaust gas recirculation path 202 is reduced or eliminated, while the cracked but unused fuel gas is retained, resulting in a reduced proportion of ammonia in the anode inlet gas fluid flow path downstream of the mixer 214 and in the fuel cell stack 10.

[0190] In this example, the getter 212 is a cryogenic getter (e.g., operable at a temperature of about 100 °C or lower). Getters operating at higher temperatures may also be used, in which case the anode exhaust gas condenser heat exchanger 206 may not be present, but the pump 210 will be subject to operating at a higher temperature.

[0191] Although the anode exhaust gas recirculation path 202 has been described as a modification to Figure 3 the system, it should be understood that the anode exhaust gas recirculation path 202 may similarly be used in combination with the exemplary systems described with reference to Figure 1 、 2 、4, 5, and 11.

[0192] In the foregoing Figure 1-12In the description, the fuel gas is exemplified as ammonia, and the cracker is exemplified as having a catalyst suitable for ammonia cracking. The described arrangement can equally be used for other fuel gases for which it is advantageous to crack the fuel gas into at least a partially cracked fuel gas for delivery to the anode inlet of at least one fuel cell stack. Methane and higher hydrocarbons can be cracked in the described arrangement. For example, the fuel gas can be (or can contain) a methanol-containing fuel gas, in which case the cracker can be provided with a catalyst suitable for methanol cracking. In this case, cracking the methanol-containing fuel before delivery to the anode inlet of at least one fuel cell stack reduces coking in the at least one fuel cell stack. This methanol cracking can be used in medium-temperature or high-temperature fuel cell systems. However, for some methanol cracking catalysts, such a high grade of heat (as found in these systems) is not necessary. Thus, the described fuel cell system is particularly useful for cracking methanol in a PEM fuel cell system, the stacks of which operate at a relatively low (or lower) temperature, but the heat source of which can be used to provide sufficient heat for methanol cracking in the arrangement described herein.

[0193] It should be understood that the arrangements described herein are applicable to other fuel gases such as methane and higher hydrocarbons, as well as ethanol and higher alcohols.

[0194] Accordingly, certain embodiments of the invention have been described above by way of example only with reference to the drawings. Each of these embodiments can be modified in detail without departing from the scope of the invention as defined in the appended claims.

Claims

1. A fuel cell system, comprising: (i) at least one fuel cell stack including at least one fuel cell and having an anode inlet, a cathode inlet, an anode exhaust outlet, and a cathode exhaust outlet; (ii) a cracker configured to crack fuel gas into at least partially cracked fuel gas and having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas; (iii) a regenerative heat exchanger; and (iv) a heat source; wherein: a) the system defines an anode inlet gas fluid flow path for delivering fuel gas from a first inlet of the regenerative heat exchanger to a first outlet of the regenerative heat exchanger, through the cracker, to a second inlet of the regenerative heat exchanger, to a second outlet of the regenerative heat exchanger and to the anode inlet of the at least one fuel cell stack; b) the heat source is configured to supply heat to the anode inlet gas fluid flow path between the first outlet of the regenerative heat exchanger and the second inlet of the regenerative heat exchanger; and c) the regenerative heat exchanger is arranged to transfer heat from the relatively high temperature at least partially cracked fuel gas from the cracker outlet to the relatively low temperature fuel gas delivered between the first inlet and the first outlet of the regenerative heat exchanger to increase the temperature of the fuel gas delivered between the first inlet and the first outlet of the regenerative heat exchanger for delivery to the cracker inlet, while reducing the temperature of the at least partially cracked fuel gas from the cracker between the second inlet and the second outlet of the regenerative heat exchanger for delivery to the anode inlet.

2. The fuel cell system according to claim 1, wherein the heat source comprises an exhaust gas burner of the fuel cell system.

3. The fuel cell system according to claim 1, wherein the heat source comprises a catalytic burner of the fuel cell system.

4. The fuel cell system according to claim 1 or claim 3, wherein the heat source is a catalytic combustion cracker heat exchanger (CCCHX) configured to catalytically combust exhaust gas from the anode exhaust outlet and the cathode exhaust outlet, the CCCHX having a catalyst for cracking fuel gas coated on the anode inlet gas fluid flow path of the CCCHX and having a catalyst for catalytically combusting exhaust gas from the anode exhaust outlet and the cathode exhaust outlet on the exhaust gas fluid flow path of the CCCHX, the catalytic combustion being configured to provide the heat source for cracking the fuel gas.

5. The fuel cell system according to any one of the preceding claims, wherein the cracker comprises a second heat exchanger.

6. The fuel cell system according to claim 5, further comprising a second gas fluid flow path, wherein the heat source is configured to supply heat to the second gas fluid flow path, and wherein the fuel cell system is arranged to transfer heat from the second gas fluid flow path to the anode inlet gas fluid flow path to provide energy for cracking.

7. The fuel cell system according to claim 6, wherein the second gas fluid flow path includes an exhaust gas fluid flow path from the anode exhaust gas outlet and the cathode exhaust gas outlet of the stack to the heat source and to the cracker.

8. The fuel cell system according to any one of claims 5 to 7, wherein the cracker has a catalyst for cracking the fuel gas, the catalyst is provided on one side of the second heat exchanger, and the catalyst forms a part of the anode inlet gas fluid flow path.

9. The fuel cell system according to any one of the preceding claims, wherein a supplementary pipeline is provided, the supplementary pipeline is configured to supply fuel gas to the heat source, and optionally further includes control software, the control software is configured to use the supplementary fuel gas to increase the temperature of the exhaust gas fluid flow path downstream of the heat source.

10. The fuel cell system according to any one of the preceding claims, wherein the anode inlet gas fluid flow path further includes a pipeline from the regenerative heat exchanger to the anode inlet, the pipeline is configured for heat exchange between the at least partially cracked fuel gas and one or both of the following: the at least one fuel cell stack, and the heat source.

11. The fuel cell system according to any one of the preceding claims, wherein a bypass or a variable valve for providing flow control is provided between the heat source and the cracker to bypass or reduce / change the heat flow from the heat source to the cracker.

12. The fuel cell system according to claim 11, wherein the bypass from the heat source is provided, the bypass is arranged to allow at least a part of the heat from the heat source to be diverted for alternative operation, or to completely bypass heating the anode inlet gas fluid flow path in the cracker.

13. The fuel cell system according to any one of the preceding claims, wherein the fuel gas is an ammonia-containing fuel gas.

14. The fuel cell system according to claim 13 when dependent on any one of claims 5 to 8, wherein the cracker has a catalyst for cracking ammonia, the catalyst is provided on one side of the second heat exchanger, and the catalyst forms a part of the anode inlet gas fluid flow path.

15. The fuel cell system according to any one of claims 1 to 12, wherein the fuel gas is a methanol-containing fuel gas.

16. The fuel cell system according to claim 15 when dependent on any one of claims 5 to 8, wherein the cracker has a catalyst for cracking methanol, the catalyst is provided on one side of the second heat exchanger, and the catalyst forms a part of the anode inlet gas fluid flow path.

17. The fuel cell system according to any one of the preceding claims, further comprising: An anode exhaust gas recirculation path configured to recirculate a portion of anode exhaust gas from the anode exhaust gas outlet of the at least one fuel cell stack to the anode inlet of the at least one fuel cell stack.

18. The fuel cell system according to claim 17, wherein the anode exhaust gas recirculation path includes an aspirator configured to remove un-cracked fuel gas from the anode exhaust gas recirculation path.

19. A method for at least partially cracking a fuel gas, comprising: Providing a system as claimed in any of the preceding claims; Flowing fuel gas through the anode inlet gas fluid flow path; And providing heat to the anode inlet gas fluid flow path via the heat source between the first outlet of the regenerative heat exchanger and the second inlet of the regenerative heat exchanger.

20. The method according to claim 19, wherein the heat source is configured to combust exhaust gas from the anode exhaust gas outlet and the cathode exhaust gas outlet, and the exhaust gas fluid flow path is configured to direct the combusted exhaust gas to the cracker at a relatively higher temperature compared to the fuel gas, and the cracker is configured to transfer heat from the relatively higher temperature combusted exhaust gas to the relatively lower temperature fuel gas.

21. The method according to claim 19 or 20, wherein there are three heat exchange stages: heat exchange from the heat source to the fuel gas; heat exchange with the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger by at least a portion of the relatively higher temperature cracked fuel gas from the cracker outlet; and heat exchange for cooling at least a portion of the relatively higher temperature cracked fuel gas by the fuel gas supply when fed between the first inlet and the first outlet of the regenerative heat exchanger.

22. The method according to any of claims 19 to 21, wherein the fuel gas is an ammonia-containing fuel gas, the method is a method of at least partially cracking ammonia into nitrogen and hydrogen, and the operating temperature of the cracker is between 550 °C and 900 °C.

23. The method according to claim 22, wherein the at least partially cracked fuel gas leaving the cracker contains less than 1000 parts per million by volume of ammonia.

24. The method according to any of claims 19 to 21, wherein the fuel gas is a methanol-containing fuel gas, the method is a method of at least partially cracking methanol into carbon dioxide gas and hydrogen, and the operating temperature of the cracker is between 250 °C and 450 °C.

25. The method according to claim 24, wherein the at least partially cracked fuel gas leaving the cracker contains less than 1000 parts per million by volume of methanol.

26. A method of starting a fuel cell system, the fuel cell system comprising: At least one fuel cell stack having an oxidant inlet and a fuel inlet, An oxidant heat exchanger for an oxidant stream reaching the oxidant inlet of the stack, A heat source for heating the at least one fuel cell stack, and A cracker for cracking fuel gas into at least partially cracked fuel gas, the cracker having a cracker inlet for receiving the fuel gas and a cracker outlet for discharging the at least partially cracked fuel gas for feeding to the fuel inlet of the fuel cell stack. The method includes: heating the at least one fuel cell stack to a first threshold temperature; and once the at least one fuel cell stack reaches the first threshold temperature, starting the flow of the fuel gas to the cracker or increasing the rate of the flow.

27. The method according to claim 26, wherein the fuel cell system is as described in any one of claims 1 to 18.

28. The method according to claim 26 or 27, wherein the oxidant is provided to the heat source via an oxidant fluid flow path, the oxidant from an oxidant source to the oxidant inlet or cathode inlet of the stack, through the stack and out of the cathode exhaust outlet of the stack to reach the heat source.

Images