FUEL CELL SYSTEMS AND METHODS

Abstract

A fuel cell system (200) and a method (900) for controlling temperature of a heat transfer fluid in a fuel cell system (200). The system (200) comprising at least one fuel cell stack (205) comprising at least one fuel cell, and having an anode inlet, an anode off-gas outlet for flow of anode off-gas. The system (200) further comprising a first heat exchanger (215) coupled to receive the anode off-gas which has been output form the anode off-gas outlet, the first heat exchanger (215) configured to exchange heat between the anode off-gas and a heat transfer fluid to cool the anode off-gas and heat the heat transfer fluid. The system (200) further comprising a second heat exchanger (230) that is configured to provide heat to the heat transfer fluid and a heat removal region (235) that is configured to remove heat from the heat transfer fluid. The system (200) further comprising a pump (240) configured to pump the heat transfer fluid around a fluid circuit (225) in a flow direction of: heat removal region (235) where thermal energy is removed, second heat exchanger (230) where thermal energy is added, first heat exchanger (215) where thermal energy is added. The method (900) comprises controlling (920, 945) the pump speed and controlling (925, 940) a mass flow rate of a medium to control the rate of heat removal in the heat removal region (235).

Claims

1. A fuel cell system comprising: at least one fuel cell stack comprising at least one fuel cell, and having an anode inlet, an anode off-gas outlet for flow of anode off-gas; a first heat exchanger coupled to receive the anode off-gas which has been output form the anode off-gas outlet, the first heat exchanger configured to exchange heat between the anode off-gas and a heat transfer fluid to cool the anode off-gas and heat the heat transfer fluid; a second heat exchanger that is configured to provide heat to the heat transfer fluid; a heat removal region that is configured to remove heat from the heat transfer fluid; and a pump configured to pump the heat transfer fluid around a fluid circuit in a flow direction of: heat removal region where thermal energy is removed, second heat exchanger where thermal energy is added, first heat exchanger where thermal energy is added.

2. The fuel cell system of claim 1, further comprising a separator to receive the anode off-gas from the first heat exchanger and configured to separate condensed water from the anode off-gas from anode off-gas containing remaining water vapour.

3. The fuel cell system of claim 1, further comprising a burner through which the anode off-gas is routed, subsequent to the separator, and remaining fuel in the anode off-gas combusted, and wherein the combustion products are routed to the second heat exchanger to provide said heat to the heat transfer fluid.

4. The fuel cell system of claim 3, further comprising a top up line configured to supply fuel to burner, wherein use of fuel by the burner is controllable to increase a heat content of the combustion products and thereby increase the temperature of the heat transfer fluid.

5. The fuel cell system of claim 1, wherein the heat removal region comprises a third heat exchanger configured to remove heat from the heat transfer fluid to another medium.

6. (canceled)

7. The fuel cell system of claim 5, wherein the other medium is a gas, and wherein the gas is driven through the third heat exchanger by a controllable fan configured to control heat transfer from the heat transfer fluid.

8. (canceled)

9. The fuel cell system of claim 1, wherein the heat removal region comprises a fourth heat exchanger in the fluid circuit configured to remove heat from the heat transfer fluid to a heat reservoir if the temperature of the heat transfer fluid is greater than the temperature of the heat reservoir and provide heat to the heat transfer fluid from the heat reservoir if the temperature of the heat transfer fluid is less than the temperature of the heat reservoir.

10. The fuel cell system of claim 9, wherein the heat reservoir comprises a hot water circuit in which water circulates.

11. The fuel cell system of claim 1, further comprising a fifth heat exchanger positioned in the fluid circuit between the heat removal region and the first heat exchanger, and the fifth heat exchanger configured to provide heat to the heat transfer fluid.

12. (canceled)

13. The fuel cell system of claim 1, wherein one or more of the pump and the rate of heat removal in the heat removal region are controllable by an algorithm to maintain a target temperature of the heat transfer fluid subsequent to the first heat exchanger.

14. (canceled)

15. A method for controlling temperature of a heat transfer fluid in a fuel cell system in which the heat transfer fluid is pumped around a fluid circuit by a pump of controllable speed and a heat removal region configured to remove heat from the heat transfer fluid to another medium, wherein a mass flow rate of the other medium is controllable to control the rate of heat removal, the method comprising: prioritising increasing pump speed over increasing the mass flow rate of the other medium as temperature of the heat transfer fluid rises, and prioritising reducing mass flow rate of the other medium over reducing pump speed as temperature of the heat transfer fluid falls.

16-18. (canceled)

19. The method of claim 15, wherein if the temperature is less than the maximum temperature of the operating range, further comprising reducing the mass flow rate of the other medium to zero.

20. (canceled)

21. The method of claim 15, wherein the temperature is a first temperature and the first temperature of heat transfer fluid is monitored subsequent to a first heat exchanger in the fluid circuit and further comprising determining that the first temperature is such that the heat transfer fluid may freeze and increasing the temperature of the heat transfer fluid and/or determining that the temperature of water condensed at the first heat exchanger and entering a storage tank subsequent to the first heat exchanger may freeze and increasing the temperature of the heat transfer fluid.

22. The method of claim 15, further comprising monitoring a water level in a tank in which water is recovered from anode off-gas for reuse in a fuel cell stack, and a) determining that an increased rate of water recovery is required to at least maintain the water level, and increasing pump speed and/or increasing mass flow rate of the other medium in order to reduce the temperature of the heat transfer fluid, or b) determining that a decreased rate of water recovery may be tolerated, and reducing pump speed and/or reducing mass flow rate of the other medium in order to increase the temperature of the heat transfer fluid.

23. The method of claim 15, further comprising monitoring a second temperature of heat transfer fluid prior to the first heat exchanger.

24. The method of claim 23, further comprising determining that the second temperature is such that the heat transfer fluid may freeze and supplying fuel to a burner configured to combust said fuel and routing the combustion products to a second heat exchanger in the fluid circuit to heat the heat transfer fluid.

25. (canceled)

26. The method of claim 15, wherein the other medium is a gas, and wherein the gas is driven by a fan of controllable speed to vary the mass flow rate of the gas and control the rate of heat removal in the heat removal region.

27. A fuel cell system comprising: at least one fuel cell stack comprising at least one solid oxide fuel cell, and having an anode inlet, an anode off-gas outlet for flow of anode off-gas; a first heat exchanger coupled to receive the anode off-gas which has been output form the anode off-gas outlet, the first heat exchanger configured to exchange heat between the anode off-gas and a heat transfer fluid to cool the anode off-gas and heat the heat transfer fluid; a second heat exchanger that is configured to provide heat to the heat transfer fluid; a heat removal region that is configured to remove heat from the heat transfer fluid; a bypass path for the heat transfer fluid to bypass the heat removal region; and a pump configured to pump the heat transfer fluid around a fluid circuit in a flow direction of: first heat exchanger where thermal energy is added second heat exchanger where thermal energy is added, heat removal region where thermal energy is removed.

28. The fuel cell of claim 27, wherein the bypass path comprises a controllable flow splitter to control a relative flow rate of the heat transfer fluid through the bypass path and through the heat removal region.

29. The fuel cell of claim 27, wherein the heat removal region comprises a fourth heat exchanger in the fluid circuit configured to remove heat from the heat transfer fluid to a heat reservoir if the temperature of the heat transfer fluid is greater than the temperature of the heat reservoir and provide heat to the heat transfer fluid from the heat reservoir if the temperature of the heat transfer fluid is less than the temperature of the heat reservoir.

30-31. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] FIG. 1 is a schematic of a prior art fuel cell system.

[0085] FIG. 2 is a schematic of a fuel cell system in accordance with the present invention.

[0086] FIG. 3 is a schematic of a fuel cell system in accordance with the present invention.

[0087] FIG. 4 is a schematic of a fuel cell system in accordance with the present invention.

[0088] FIG. 5 is a schematic of a fuel cell system in accordance with the present invention.

[0089] FIG. 6 is a schematic of a fuel cell system in accordance with the present invention.

[0090] FIG. 7 is a schematic of a fuel cell system in accordance with the present invention.

[0091] FIG. 8 is a schematic of a fuel cell system in accordance with the second aspect of the present invention.

[0092] FIG. 9 illustrates control processes for controlling a fuel cell system in accordance with the invention.

[0093] FIG. 10 Illustrates control processes for controlling a fuel cell system in accordance with the invention.

[0094] For Illustrative purposes only, the figures only indicate a single fuel cell stack. In various embodiments, (not shown) multiple fuel cell stacks are provided, and in still further embodiments multiple fuel cell stacks each comprising multiple fuel cells are provided. It will be appreciated that the anode and cathode inlets, outlets (off-gas), ducting, manifolding, and temperature sensors and their configuration are modified as appropriate for such embodiments, and will be readily apparent to a person of ordinary skill in the art.

[0095] In the following figures and description like reference numerals will be used for like elements in different figures.

DETAILED DESCRIPTION

[0096] Referring to FIG. 2, fuel cell system 200 is shown. The fuel cell system 200 includes a fuel cell stack 205 is a metal-supported IT-SOFC fuel cell stack, comprising metal-supported IT-SOFC fuel cells, but may be any other type of fuel cell stack. Each fuel cell has an anode side, electrolyte layer, and cathode side. Each fuel cell layer in the fuel cell stack is separated by an electrically conducting gas impermeable metal interconnect plate (interconnector) (not shown). Fuel cell stack endplates and compression means (not shown) are also provided. Reference herein to fuel cell is to the full set of fuel cells which form the fuel cell stack. An electrical load is placed across the fuel cell. The fuel cell stack has an anode inlet and anode outlet in fluid communication with the anode of the fuel cells in the fuel cell stack. The anode inlet provides fuel to the anode of the fuel cells. The fuel may be hydrogen gas or methane, which is produced from a supply of natural gas and water vapour via reformation in a reformer (not shown). Alternatively, the fuel may be natural gas mixed with water vapour which is subsequently reformed to hydrogen or methane within the fuel cell stack. The anode outlet is an exhaust for fluids from the anode side of the fuel cells in the fuel cell stack, these fluids will be referred to as anode off-gas and comprise unused fuel, and water vapour.

[0097] A fuel cell stack anode inlet is in fluid flow communication with fuel cell anode inlet for the flow of anode inlet gas to the anode side of fuel cell. A fuel cell anode outlet is in fluid flow communication with fuel cell stack anode off-gas outlet for the flow of anode off-gas.

[0098] A fuel cell stack cathode inlet is in fluid flow communication with a fuel cell cathode inlet for the flow of cathode inlet gas to the cathode side of fuel cell. A fuel cell cathode outlet is in fluid flow communication with fuel cell stack cathode off-gas outlet for the flow of cathode off-gas.

[0099] Burner 210 (which may also be referred to as a tail gas burner) is in fluid flow communication with fuel cell stack anode and cathode off-gas outlets and has a burner exhaust, anode off-gas inlet and cathode off-gas inlet. Burner 210 lies on a fluid flow path from fuel cell stack anode and cathode off-gas outlets to tail-gas burner exhaust, and is configured for burning anode and cathode off-gases and producing a tall-gas burner off-gas. The burner may have a supply of fuel (also referred to as top-up fuel) from a fuel supply for burning in the burner. The burner off-gas may be routed from the burner 210 via an optional non-return valve (not shown) to a flue (not shown) to cool the burner off-gas and release the products to the environment surrounding the fuel cell system 200. Various components, generally represented by a double slash “//”, may be positioned between the burner and the flue, through which the burner off-gas is routed.

[0100] An anode off-gas fluid flow path is defined from fuel cell stack anode off-gas outlet to tank 220 (also referred to as separator) to an anode off-gas inlet of tail gas burner 210. The anode off-gas may pass through other components between the tank 220 and the burner 210.

[0101] An anode inlet gas fluid flow path (not shown in full) is defined from a fuel source to the fuel cell anode inlet (optionally via a steam reformer). Water, sourced from the tank 220, is added to the fuel for reformation of the fuel in the fuel cell stack or in a steam reformer (if present). Various components, generally represented by a double slash “//”, may be positioned on the anode inlet gas fluid flow path between the tank 220 and the fuel cell stack 205. These various components may include a reformer to reform fuel, an evaporator to evaporate fuel and water, and a heat exchanger to pre heat the anode (and cathode) inlet gas by transfer of heat from the burner off-gas as described in WO2015004419A1. These various components condition the anode inlet gas for use in the stack.

[0102] A cathode inlet gas flow path (not shown) is defined from an oxidant source to the fuel cell stack cathode inlet (and may pass through other components, such as heat exchangers to heat the oxidant before entry to the fuel cell, as described in WO2015004419A1). The cathode inlet gas flow path may include flow from a blower to and anode off-gas heat exchange to an air pre-heater heat exchanger to a reformer heat exchanger, to the fuel cell stack cathode inlet.

[0103] A cathode off-gas fluid flow path (not shown) is defined from fuel cell stack cathode off-gas outlet to cathode off-gas inlet of the burner 210.

[0104] Fuel cell system 200 includes a fluid circuit 225 configured to transport a heat transfer fluid between various components. The heat transfer fluid passes through numerous heat exchangers, each of which may comprise at least one heat exchange element or heat exchange surface, and are configured to transfer heat (otherwise referred to as thermal energy) between a first fluid, for example the heat transfer fluid, and a second fluid. The heat exchangers may be any type of heat exchanger, and may be co-flow or counter-flow.

[0105] The fluid circuit 225 of FIG. 2 comprises a first heat exchanger 215, a second heat exchanger 230, a heat removal region 235, and a pump 240. The pump is configured to pump the heat transfer fluid around the fluid circuit in a flow direction of: heat removal region 235, second heat exchanger 230, and first heat exchanger 215. The pump 240 is shown located in the fluid circuit 225 between the heat removal region 235 and the second heat exchanger 240, but alternatively be located at any suitable position within the fluid transfer circuit 225 which allows the pump 240 to pump the heat transfer fluid around the fluid transfer circuit 225. The pump may be a variable speed pump, the speed controllable to control a flow rate of heat transfer fluid around the fluid transfer circuit 225. The fluid transfer circuit 225 may be a continuous or sealed fluid circuit.

[0106] The heat transfer fluid, which may also be referred to as heat exchange fluid, may be any one of water, refrigerant fluid, anti-freeze fluid, oil, mixed fluids, fuel and air.

[0107] The first heat exchanger 215, also referred to as the anode off-gas heat exchanger or anode off-gas (AOG) condenser, is in fluid communication with the stack 205 and coupled to receive anode off-gas from the stack 205. The first heat exchanger 215 exchanges heat between the anode off-gas and the heat transfer fluid in the fluid circuit 225. The anode off-gas typically has a high temperature (for example, 400-800 C.) and so thermal energy is transferred to the heat transfer fluid at first heat exchanger 215.

[0108] The second heat exchanger 230 exchanges heat between the heat transfer fluid in the fluid circuit 225 and another fluid is a further circuit (not shown). Thermal energy is transferred to the heat transfer fluid at the second heat exchanger 230.

[0109] The heat removal region 235 is configured to remove heat from the heat transfer fluid. Thermal energy is removed from the heat transfer fluid at the heat removal region 235 to maintain the heat transfer fluid in an operating range of temperature. The heat removal region 235 may comprise one or more of a heat exchanger for transfer of heat from the heat transfer fluid to another fluid or a pipe for transferring heat from the heat transfer fluid to the surroundings of the pipe. The pipe may comprise a heating system (for example, an underfloor heating system).

[0110] The fluid transfer circuit 225 is provided with temperature sensors to measure the temperature of the heat transfer fluid. A first temperature sensor 245 is positioned to measure the temperature of the heat transfer fluid between the first heat exchanger 215 and the heat removal region 235. The first temperature sensor 245 measures temperature T.sub.B, which is referred to as the anode off-gas (AOG) condensing temperature. A second temperature sensor 250 is positioned to measure the temperature of the heat transfer fluid between the second heat exchanger 230 and the first heat exchanger 215. The second temperature sensor 250 measures temperature T.sub.A, which is referred to as the AOG inlet temperature.

[0111] In use, the pump 240 is operated to pump the heat transfer fluid around the fluid circuit 225 in a flow direction of: heat removal region where thermal energy is removed, second heat exchanger where thermal energy is added, first heat exchanger (AOG) where thermal energy is added. Heat is transferred to the heat transfer fluid at the second heat exchanger 230. The temperature of the heat transfer fluid subsequent to the second heat exchanger 230 is measured using the second temperature sensor 250. Subsequent to the second heat exchanger 230, the heat transfer fluid passes through the first heat exchanger 215, in which heat is transferred from the anode off-gas to the heat transfer fluid. The temperature of the heat transfer fluid subsequent to the first heat exchanger 215 is measured using the first temperature sensor 245. Subsequent to the second heat exchanger 230, the heat transfer fluid passes through the heat removal region 235, in which heat is transferred from the heat transfer fluid and may be usefully used, for example to heat a room or a hot water system.

[0112] The speed of the pump 240 (and therefore the rate of flow of heat transfer fluid around the fluid circuit 225) is controlled by an algorithm, which will be described in more detail with reference to

[0113] FIGS. 9 and 10. The algorithm monitors the temperature of the heat transfer fluid via first temperature sensor 245 and/or second temperature sensor 250 and adjusts the pump speed to maintain the heat transfer fluid within an operating range of temperature. The algorithm may increase the pump speed (thereby increasing the flow rate) to reduce the temperature of the heat transfer fluid, for example if the heat transfer fluid reaches an upper limit of the operating range of temperature, as a result of increasing the flow rate the temperature of the heat transfer fluid typically decreases. The algorithm may decrease the pump speed (thereby decreasing the flow rate) to increase the temperature of the heat transfer fluid, for example if the heat transfer fluid reaches a lower limit of the operating range of temperature, as a result of decreasing the pump speed the temperature of the heat transfer fluid typically increases.

[0114] Fuel is provided to the anode inlet (not shown) of fuel cell stack 205 for supply of gas to the anode(s) of the fuel cell(s), Water is sourced from the tank 220, vaporised, and added to the fuel. The water is used for reformation of the fuel in the fuel cell stack or in a steam reformer (if present) prior to the fuel cell stack.

[0115] Hot anode off-gas from the fuel cell stack anode off-gas outlet is routed to the first heat exchanger 215, where thermal energy is removed from the anode off-gas and transferred to the heat transfer fluid. As a result, the anode off-gas is cooled significantly. The anode off-gas is subsequently routed via an anode off-gas fluid flow path 216 to the tank 220, where condensate (water) is recovered from the anode off-gas and stored in the tank. As a result, the humidity of the anode off-gas is reduced and it may be referred to as dry anode off gas. The dry anode off-gas is routed (via path 217) from the tank 220 to the burner 210. The dry anode off-gas is mixed with oxidant (not shown) and combusted in the burner 210 to remove any remaining fuel, the combustion products, or burner off-gas, are routed to a flue (not shown) via path 218 and released to atmosphere. Ideally, little unused fuel is present in the anode off-gas and so little fuel is burnt in the burner 210. The oxidant combusted in the burner may be cathode off-gas routed from the fuel cell stack 205.

[0116] The amount of water recovered from the anode off-gas at the tank 220 (and so humidity of the dry anode off-gas) is dependent upon the temperature of the dry anode off gas which, in turn, is dependent upon the temperature of the heat transfer fluid at the entry to and exit from the first heat exchanger 215. If the heat transfer fluid is warmer, then less water is recovered from the anode off-gas than if the heat transfer fluid is cooler, Water is used for reformation of supply fuel to hydrogen, but is produced at the anode during operation of the fuel cell. In order to enable the fuel cell system to be self-sufficient with water, the algorithm may monitor the level of water in the tank and control the temperature of the heat transfer fluid in order to increase or decrease the rate at which water is recovered in the tank, to maintain the level of water in the tank within an operating range. The algorithm may determine that the level of water in the lank is low, and increase the pump speed to decrease the temperature of the heat transfer fluid, thereby decreasing the humidity of the dry anode off-gas and increasing the amount of water recovered to the tank 220.

[0117] Coking of system components between the tank and burner including the burner can occur in certain circumstances of the dry anode off-gas composition being unfavourable and the components being at unfavourable temperatures where coking can occur. Likelihood of coking can be reduced by increasing the water vapour content of the AOG. The algorithm may determine that the level of water in the tank is adequate or high, and decrease the pump speed to increase the temperature of the heat transfer fluid, thereby increasing the humidity of the dry anode off-gas and decreasing the amount of water recovered to the tank 220. A higher humidity of dry anode off-gas is favoured to reduce coking in the anode off-gas stream in components downstream of the tank 220, for example at the burner 210. Thus, the algorithm may maintain the heat transfer fluid at a temperature at which the level of water in the tank is constant (i.e. the level neither decreases nor increases).

[0118] Referring to FIG. 3, a fuel cell system 300 is shown. Fuel cell system 300 is a variant of the fuel cell system 200 of FIG. 2. In the variant shown in FIG. 3, the burner off gas is routed to the second heat exchanger 331 and is the another fluid referred to above. The second heat exchanger 230 exchanges heat between the heat transfer fluid in the fluid circuit 225 and the burner off-gas. Thermal energy is transferred from the burner off-gas to the heat transfer fluid at the second heat exchanger 230. The burner off-gas leaves the second heat exchanger 230 and passes though an optional non-return valve (not shown) before exiting the fuel cell system via an exhaust flue assembly to atmosphere or another extraction system.

[0119] The burner may be equipped with a supply of fuel additional to any fuel in the anode off-gas. The additional fuel may be referred to as top up fuel, and originates from the same source as the fuel used in the fuel cell stack 205. Top up fuel may be burnt in the burner in order to raise the temperature of the burner off-gas and/or increase the heat transferred to the heat transfer fluid at the second heat exchanger 331. The algorithm may control burning of the top up fuel to increase the temperature of the heat transfer fluid, for example if the heat transfer fluid is at risk of freezing.

[0120] Referring to FIG. 4, a fuel cell system 400 is shown. Fuel cell system 400 is a variant of the fuel cell system 200 of FIG. 2. In the variant shown in FIG. 4, the heat removal region is represented as a third heat exchanger 436 and positioned within the fluid circuit subsequent to the pump 240 and prior to the second heat exchanger 230.

[0121] The third heat exchanger 436 is configured to remove heat from the heat transfer fluid and transfer heat to another fluid. In an example, the another fluid is a gas. The gas may be air, the air is warmed at the third heat exchanger and can be used to heat an enclosed volume. For example, the enclosed volume may be the cabin of a vehicle, in which case the third heat exchanger may be a radiator (e.g. the vehicle's radiator), or the enclosed volume may be air enclosed within rooms of a building. In an alternative example, the another fluid is a liquid. The liquid may circulate in a hot water circuit to heat a medium. The hot water circuit may comprise a heating system in a house or in a motive application, for example a mobile home (e.g. campervan). The liquid may be water and be used in a house or mobile home as a source of hot water.

[0122] Referring to FIG. 5, a fuel cell system 500 is shown. Fuel cell system 500 is a variant of the fuel cell system 400 of FIG. 4. In the variant shown in FIG. 5, third heat exchanger 537 is configured to remove heat from the heat transfer fluid and transfer heat to a gas. The gas is driven through the third heat exchanger 537 by a fan 555. The fan 555 is controllable by the algorithm to vary the mass flow rate of gas through the third heat exchanger 537 and so configured to control heat transfer from the heat transfer fluid to the gas and thereby control the temperature of the mass transfer fluid. The mass flow rate of gas through the third heat exchanger 537 is proportional to the speed (rotations per time) of the fan. The fan is driven by electricity, the electricity is supplied by the fuel cell stack and the algorithm seeks to minimise usage of the fan, for example by increasing pump speed over increasing fan speed. The gas may be air, the air is warmed at the third heat exchanger and can be used to heat an enclosed volume. For example, the enclosed volume may be the cabin of a vehicle, in which case the third heat exchanger may be a radiator (e.g. the vehicle's radiator), or the enclosed volume may be air enclosed within rooms of a building.

[0123] Referring to FIG. 6, a fuel cell system 600 is shown. Fuel cell system 600 is a variant of the fuel cell system 400 of FIG. 4. In the variant shown in FIG. 6, the pump 240 used for pumping the heat transfer fluid around the fluid circuit 225 is positioned in the fluid circuit between the second hear exchanger 230 and the first heat exchanger 215, i.e. the pump 240 is downstream of the second heat exchanger 230 and upstream of the first heat exchanger 215.

[0124] FIG. 6 is an example in which the heat removal region comprises the third heat exchanger 638 configured to remove heat from the heat transfer fluid and transfer heat to a liquid. The liquid circulates in liquid circuit 660, and is pumped around the circuit by a pump 665. The liquid may be water. Other components in the fluid circuit 660 are represented by the double slash “//”. A heat sink is located in the fluid circuit 660 to remove heat from the liquid circuit 660.

[0125] The liquid circuit 660 may circulate to heat a medium, in which case the liquid circuit 660 may be a continuous or sealed circuit. In this case, the hot water circuit may comprise a heating system in a house or in a motive application, for example a mobile home (e.g. campervan), and heat may be removed from the liquid circuit 660 via a radiator or a pipe for transferring heat to its surroundings, such as a heating system (e.g. underfloor heating system). Alternatively or additionally, the liquid circuit 660 may be used in a house or mobile home as a source of hot water, in which case the liquid circuit is non-continuous, and cool water is introduced to the liquid circuit 660 to replace hot water taken from the circuit.

[0126] Referring to FIG. 7, a fuel cell system 700 is shown. Fuel cell system 700 is a variant of the fuel cell system 400 of FIG. 5. In the variant shown in FIG. 7, a fourth heat exchanger 770 and a fifth heat exchanger 775 are positioned within the fluid circuit 225. It is to be understood that the fourth heat exchanger 770 and the fifth heat exchanger 775 are optional and one may be present without the other.

[0127] The fourth heat exchanger 770 is positioned upstream of the third heat exchanger 537 and downstream of the first heat exchanger 215 subsequent to the first temperature sensor 245, in other words the fourth heat exchanger 770 is placed in the fluid circuit 225 between the first heat exchanger 215 and the third heat exchanger 537. The fourth heat exchanger 770 exchanges heat between the heat transfer fluid and a heat reservoir (not shown). The fourth heat exchanger 770 removes heat from the heat transfer fluid to the heat reservoir reservoir if the temperature of the heat transfer fluid is greater than the temperature of the heat reservoir and provides heat to the heat transfer fluid from the heat reservoir if the temperature of the heat transfer fluid is less than the temperature of the heat reservoir. The heat reservoir may comprise a liquid circuit, similar to that described with reference to FIG. 6 above. As such, heat removed from the heat transfer fluid at the fourth heat exchanger 770 serves a useful purpose, and the heat transferred within the fourth heat exchanger 770 is maximised by positioning the fourth heat exchanger 700 at the location in the fluid circuit 225 at which the heat transfer fluid is at its hottest (subsequent, e.g. immediately subsequent, to the first heat exchanger 215 and prior to the third heat exchanger 537).

[0128] The fifth heat exchanger 775 is positioned upstream of the first heat exchanger 215 prior to the first temperature sensor 245 and downstream of the second heat exchanger 331, in other words the fifth heat exchanger 775 is placed in the fluid circuit 225 between the second heat exchanger 331 and the first heat exchanger 215. The fifth heat exchanger 775 may be a heat source to provide heat to the heat transfer fluid or a heat sink to remove heat from the heat transfer fluid. In the case that the fifth heat exchanger 775 is a heat sink, it may be used to heat air in a building or vehicle (similar to the third heat exchanger 436, 537, 638 as described above), or it may be used to heat water for purposes of heating a building or vehicle, or to provide a supply of hot water (similar to the fourth heat exchanger 770 described above). The fifth heat exchanger 775 may represent more than one heat exchanger, the more than one heat exchanger being any combination of heat sinks and heat sources. For example, in an automotive application of the system 700, the fifth heat exchanger may exchange heat between the heat transfer fluid and other components of the automotive system such as cooled inverters, batteries, or electric motors, in order to cool the same and allow the heat transferred to the heat transfer fluid to be used in fluid circuit 225 by increased temperature at the first heat exchanger 215 (thereby reducing coking) and to heat other media external to the fluid circuit 225 via the third heat exchanger 537 and fifth heat exchanger 770. Further, in an automotive application the fifth heat exchanger 775 may remove heat from the heat transfer fluid and use it to heat cabin air.

[0129] In cases where the fuel supplied to the fuel cell stack originates from a pressure compressed fuel tank, the fifth heat exchanger 775 may remove heat from the heat transfer fluid and use it to heat the fuel upon exiting the tank (the temperature of the fuel as it exits the tank is low because of expansion of the fuel as it exits the high pressure tank).

[0130] In an alternative, the fifth heat exchanger 775 is positioned upstream of the second heat exchanger 331 and downstream of the third heat exchanger 537, in other words the fifth heat exchanger 775 is placed in the fluid circuit 225 between the third heat exchanger 537 and the second heat exchanger 331. This alternative arrangement is preferable if the fifth heat exchanger 775 is a heat sink to remove heat from the heat transfer fluid such that the heat transfer fluid upon entry to the first heat exchanger 215 is not cooled by a heat sink positioned in the fluid circuit 225 between it and the second heat exchanger 331.

[0131] Further shown in FIG. 7 are typical temperatures for a combined heat and power stationary application which is able to provide power (generated at the fuel cell stack) and heat (recovered from the heat transfer fluid at the fourth heat exchanger 770 and/or the third hear exchanger 537) to a building or group of buildings. The typical temperatures shown in FIG. 7 are for the case where the fourth heat exchanger 770 removes heat from the heat transfer fluid and the fifth heat exchanger 775 provides heat to the heat transfer fluid. The typical temperatures are appropriate for the case where each heat exchanger is a parallel flow heat exchanger, nonetheless other types of heat exchangers may be used in the fuel cell system, for example counter-flow heat exchangers. A temperature of around 60 deg C. is achieved in the heat transfer fluid at the first temperature sensor 245, subsequent to the first heat exchanger 215, which is found to be an ideal temperature to recover sufficient water in the tank 220 and minimise coking in the components, including burner 210, through which the anode off-gas and burner off-gas passes (it will be understood that the specific temperature at the first temperature sensor required to balance water recover and coking is a function of fuel utilisation and based on operating space analysis).

[0132] As shown in FIG. 7, the temperature T1 of the heat transfer fluid subsequent to the third heat exchanger 537 is low. Heat is transferred to the heat transfer fluid at the second heat exchanger 331 and so the temperature T2 of the heat transfer fluid subsequent to the second heat exchanger 331 is greater than T1 (T2>T1). Heat is transferred to the heat transfer fluid at the fifth heat exchanger 775 and so the temperature T3 of the heat transfer fluid subsequent to the fifth heat exchanger 775 is greater than T2 and T1 (T3>T2>T1). Heat is transferred to the heat transfer fluid at the first heat exchanger 215 and so the temperature T4 of the heat transfer fluid subsequent to the first heat exchanger 215 is greater than T3, T2 and T1 (T4>T3>T2>T1). Heat is removed from the heat transfer fluid at the fourth heat exchanger 770 and so the temperature T5 of the heat transfer fluid subsequent to the fourth heat exchanger 770 is less than T4 (T5<T4). Heat is removed from the heat transfer fluid at the third heat exchanger 537 and so the temperature T1 of the heat transfer fluid subsequent to the third heat exchanger 537 is less than T5 (T1<T5).

[0133] In the example temperatures shown in FIG. 7, the medium to which heat is transferred at the fourth heat exchanger 770 is relatively warm (or has low capacity for exchange of heat) and so the temperature of the heat transfer fluid is reduced by a relatively small amount at the fourth heat exchanger 770, such that T5=T3, and a correspondingly larger temperature drop is evident between T5 and T1 via heat removed at the third heat exchanger 537. If the medium to which heat is transferred at the fourth heat exchanger 770 is relatively cool (or has high capacity for exchange of heat) and so the temperature of the heat transfer fluid is reduced by a relatively larger amount at the fourth heat exchanger 770, such that T5<13 (and T5=12 or T5<T2 but T5>T1), and a correspondingly lesser temperature drop is evident between T5 and T1 via heat removed at the third heat exchanger 537, because a lower rate of heat transfer from the heat transfer fluid is required at the third heat exchanger to maintain the heat transfer fluid within an operating temperature range. In such a case, the speed of the fan 555 may be zero (the fan is off) and so heat transfer from the heat transfer fluid at the third heat exchanger 537 is minimal, T5=T1, and the majority of heat removal from the heat transfer fluid is at the fourth heat exchanger 770 (where it may be used as described above, thereby increasing the overall efficiency of the system).

[0134] Table 1 summarises a number of example use cases described with respect to FIGS. 2-7 from the perspective of “heat in” to the heat transfer fluid in the fluid circuit 225, 825 (i.e. heat transferred to the heat transfer fluid at the respective heat exchanger) and “heat out” from the heat transfer fluid in the fluid circuit 225, 825 (i.e. heat transferred from the heat transfer fluid to some other medium at the respective heat exchanger). In the table, “HX” is used as shorthand for “heat exchanger”. It will be understood that the fourth heat exchanger 770, where present, can be configured to transfer heat to or from the heat transfer fluid, or can be operated as a heat reservoir to transfer heat to or from the heat transfer fluid depending upon current operating conditions, as is shown by the example use case of FIG. 7, options A-D below. It will be understood that the fifth heat exchanger, where present, can be configured to transfer heat to or from the heat transfer fluid, as is shown by the example use case of FIG. 7, options A-D below. FIG. 7, option A corresponds to the typical temperatures shown in that figure.

TABLE-US-00001 TABLE 1 Second HX Third HX 436, Fourth HX Example use case First HX 215 230, 331 537, 638 770 Fifth HX 775 FIG. 2 Heat in Heat in Optional as part of heat Not present removal region 235 FIG. 3 Heat in Heat in Optional as part of heat Not present removal region 235 FIG. 4 Heat in Heat in Heat out Not present Not present FIG. 5 Heat in Heat in Heat out Not present Not present FIG. 6 Heat in Heat in Heat out Not present Not present FIG. 7, option A Heat in Heat in Heat out Heat out Heat in FIG. 7, option B Heat in Heat in Heat out Heat in Heat in FIG. 7, option C Heat in Heat in Heat out Heat out Heat out FIG. 7, option D Heat in Heat in Heat out Heat out Heat in FIG. 8, option A Heat in Heat in Heat out Heat out Heat in FIG. 8, option B Heat in Heat in Heat out Heat out Heat out FIG. 8, option C Heat in Heat in Heat out Heat in Heat in FIG. 8, option D Heat in Heat in Heat out Heat in Heat out

[0135] Various use cases for the options given in table 1 are discussed above in reference to FIGS. 2-8. Generally, in the use cases of table 1, heat is removed from the heat transfer fluid at the third heat exchanger is used to heat a volume of air, or is expelled as waste heat (particularly in the cases where useful heat is recovered from the heat transfer fluid using the fourth heat exchanger).

[0136] Generally, in the use cases where heat is removed from the heat transfer fluid at the fourth heat exchanger, that heat is used to heat a liquid, typically water for use in a hot water system (to supply hot water to taps) or to heat a volume of air via radiators. This is in contrast to heating of air at the third heat exchanger because the temperature of the heat transfer fluid entering the fourth heat exchanger is higher than that entering the third heat exchanger, and so a larger amount of thermal energy can be transferred out of the heat transfer fluid at the fourth heat exchanger than at the third heat exchanger. The liquid with which thermal energy is exchanged at the fourth heat exchanger may, under certain circumstances (e.g. FIG. 7, option 8), provide heat to the heat transfer fluid (i.e. the fourth heat exchanger acts as a heat reservoir), which reduces the warm up time of the fuel cell system from a dormant or off state.

[0137] Generally, in the use cases where heat is transferred to the heat transfer fluid at the fifth heat exchanger, that transfer of heat is used to provide cooling to components external to the fuel cell system but within a wider system of which the fuel cell system is a part. Waste heat expelled by those components is usefully converted by the fuel cell system to raise the temperature of the heat transfer fluid to avoid coking, and may be usefully transferred out of the fuel cell system via the third and/or fourth heat exchangers. Generally, in the use cases where heat is removed from the heat transfer fluid at the fifth heat exchanger, that heat is used to heat other components which require only a small amount of thermal energy.

[0138] Referring to FIG. 8, a fuel cell system 800 is shown. Fuel cell system 800 is an alternative to the fuel cell systems described with reference to FIGS. 2 to 7. Fuel cell system 800 comprises a fuel cell stack 205, first heat exchanger 215, tank 220, and burner 210 as described above. In fuel cell system 800, the heat transfer fluid circulates in fluid circuit 825, and pumped around the fluid circuit 825 by pump 240. The fluid circuit 825 comprises the pump 240, first heat exchanger 215, fifth heat exchanger 775, second heat exchanger 331, fourth heat exchanger 770, and third heat exchanger 537. The pump is configured to pump the heat transfer fluid around the fluid circuit 825 in a flow direction of: pump 240, first heat exchanger 215, fifth heat exchanger 775, second heat exchanger 331, fourth heat exchanger 770, and third heat exchanger 537. Similar to the system 700 described above with reference to FIG. 7, the fourth heat exchanger 770 and fifth heat exchanger 775 are optional and one or both need not be present in the fuel cell system 800 of FIG. 8. Similar to the system 700 described above with reference to FIG. 7, the fourth heat exchanger 770 and the third heat exchanger 537 represent a heat removal region in which heat may be transferred from the heat transfer fluid. The first temperature sensor 245 is positioned subsequent to the first heat exchanger (in the fluid circuit between the first heat exchanger 215 and the fifth heat exchanger 775, or second heat exchanger 331 if the fifth heat exchanger 775 is not present). The second temperature sensor 250 is positioned prior to the first heat exchanger (in the fluid circuit between the pump 240 and the first heat exchanger 215).

[0139] The fuel cell system 800 of FIG. 8 includes a bypass path 885 for heat transfer fluid to allow at least a portion of the heat transfer fluid to bypass (i.e. not flow through) the heat removal region. A valve is positioned in the fluid circuit 825 between the second heat exchanger 331 and the fourth heat exchanger 770 (or between the second heat exchanger 331 and the third heat exchanger 537 if the fourth heat exchanger is not present). The valve splits the heat transfer fluid between flow through the heat removal region (through the continuation path 825a, which is a continuation of the fluid circuit 825) and the bypass path 885. A portion of the heat transfer fluid passes through the bypass path 885, while the remainder of the heat transfer fluid passes through the heat removal region (i.e. through third heat exchanger 537 and fourth heat exchanger 770). The bypass path and the path 825a through the heat removal region rejoin subsequent to the heat removal region at join point 881. Join point 881 is prior to the pump 240. The pump 240 may be positioned at any location in the fluid circuit 825 (i.e. the pump 240 is not positioned on the path 825a or on the bypass path 885.

[0140] The proportion of heat transfer fluid directed through the bypass path 885 and through the heat removal region is controlled by the control valve 880, which may be adjustable. The control valve may be adjusted to direct a relatively greater proportion of heat transfer fluid around the bypass path 885 (i.e. an increased mass flow rate of heat transfer fluid around the bypass path 885 and a correspondingly reduced mass flow rate of heat transfer fluid through the heat removal region) to increase the temperature of the heat transfer fluid. Conversely, the control valve may be adjusted to direct a relatively greater proportion of heat transfer fluid through the heat removal region (i.e. an increased mass flow rate of heat transfer fluid through the heat removal region and a correspondingly reduced mass flow rate of heat transfer fluid around the bypass path 885) to decrease the temperature of the heat transfer fluid. Adjustment of the control valve is controlled by the algorithm to achieve a desired temperature of heat transfer fluid (at the first temperature sensor 245 and/or second temperature sensor 250) and a desired rate of water recovery at the tank 220. As described above, decreasing the temperature of the heat transfer fluid causes an increased rate of water collection in the tank 220 and decreased humidity in the dry anode off-gas and so increased chance of coking downstream of the tank 220 while increasing the temperature of the heat transfer fluid causes a decreased rate of water collection in the tank 220 and increased humidity in the dry anode off-gas and so decreased chance of coking downstream of the tank 220.

[0141] FIG. 9 is a flow diagram representing a method 900 for control of the fuel cell systems described with reference to FIGS. 2-8. The method 900 is implemented by an algorithm to control the pump speed of pump 240 to control the mass flow rate of the heat transfer fluid around the fluid circuits 225, 825. The method 900 is implemented by an algorithm to control the mass flow rate of another medium to control the heat removed from the heat transfer fluid in the heat removal region. The method shown in FIG. 9, and described below, takes air as the another medium and so the mass flow rate of the another medium is controlled by controlling the fan 555 so control heat removal at the third heat exchanger 537. Equally, the another medium may be a liquid and the mass flow rate of the liquid controlled by controlling pump 665 to control the mass flow rate of liquid and so control heat removal at the third heat exchanger 638.

[0142] There exists a non-zero minimum mass flow rate of heat transfer fluid around the fluid circuit, while the minimum mass flow rate of the gas through the third heat exchanger is zero. A non-zero mass flow rate of the gas typically requires usage of electricity produced by the fuel cell stack to drive the gas through the third heat exchanger using fan 555. As temperature rises under closed circuit control, the pump is turned up to a maximum pump flow rate before the fan is turned on or turned up. And as temperature falls, the fan is turned down or turned off before the pump is turned down. Therefore method 900 prioritises use of the pump to drive the heat transfer fluid through the fluid circuit rather than use of the fan 555 to drive gas through the third heat exchanger.

[0143] The method monitors temperature T.sub.B, which is referred to as the anode off-gas (AOG) condensing temperature, using the first temperature sensor 245 and monitors temperature T.sub.A, which is referred to as the AOG inlet temperature, using the second temperature sensor 250. AOG inlet temperature (T.sub.A) and AOG condensing temperature (T.sub.B) are compared with a number of target temperatures: minimum AOG condensing temperature to avoid coking (Min AOGC T), maximum AOG outlet temperature to avoid running out of water (Max AOGC T), and the freezing point of the heat transfer fluid (0° C. in the example of FIG. 9).

[0144] The method 900 starts at start 905. At 910, if the AOG condensing temperature (T.sub.B) is greater than Max AOGC T, it is determined at 915 whether the pump is at its maximum speed. If it is determined that the pump is not at its maximum speed, then at 920 the pump speed is increased in order to increase the mass flow rate of the heat transfer fluid and thereby aim to reduce the temperature of the heat transfer fluid. If it is determined that the pump is at its maximum speed, then at 925 the fan speed is increased in order to increase the rate of heat removal at the third heat exchanger. Subsequent to 920 and 925 the method returns to start 905, incorporating a suitable delay (not shown) to allow the effect of the increase in fan or pump speed to have an effect on the temperature of the heat transfer fluid. The delay is a control loop response time, which may comprise a proportional-integral-derivative (PID) controller for each of the fan and pump, each PID controller having a time constant which characterizes the delay. The PID controller for the fan in general has a different time constant than that for the pump.

[0145] At 930, if the AOG condensing temperature (T.sub.B) is between the Max AOGC T and Min AOGC T (this may be referred to as the heat transfer fluid being within an operating range of temperatures), it is determined at 935 whether the fan is on. If it is determined that the fan is on, then at 940 the fan speed is reduced. The fan speed may be reduced to zero. If it is determined that the fan is not on, then at 945 the pump speed is reduced. The pump speed may be reduced to a minimum pump speed. Subsequent to 940 and 945 the method returns to start 905, incorporating a suitable delay (similar to that described above) to allow the effect of the decrease in fan or pump speed to have an effect on the temperature of the heat transfer fluid.

[0146] At 950, if the AOG condensing temperature (T.sub.B) is less than the Min AOGC T and AOG inlet temperature (T.sub.A) is greater than the freezing point of the heat transfer fluid (e.g. 0 deg C. for water), it is determined at 955 whether the fan is on. If it is determined that the fan is on, then at 940 the fan speed is reduced. The fan speed may be reduced to zero. If it is determined that the fan is not on, then at 945 the pump speed is reduced. The pump speed may be reduced to a minimum pump speed. Subsequent to 940 and 945 the method returns to start 905, incorporating a suitable delay (similar to that described above) to allow the effect of the decrease in fan or pump speed to have an effect on the temperature of the heat transfer fluid.

[0147] At 960, if the AOG inlet temperature (T.sub.A) is less than the freezing point of the heat transfer fluid (e.g. OC for water), then it is determined that the temperature of the heat transfer fluid needs to be increased. The AOG inlet temperature (T.sub.A) may be less than the freezing point of the heat transfer fluid if the fuel cell system is in an off or dormant state, if it is operated in a cold environment, or if the second and/or third and/or fourth heat exchanger, are exposed to ambient atmospheric conditions in some instalments. As a result, at 940 the fan speed is reduced. The fan speed may be reduced to zero. The pump speed may also be reduced at 945. In order to introduce heat into the system (in particular if the fuel cell system is in a dormant or off state), at 965 the heat transferred to the heat transfer fluid at the second heat exchanger is increased. This may be effected by lighting the burner 210 and burning top up fuel therein, the heat produced being transferred to the heat transfer fluid at the second heat exchanger and circulated around the fluid circuit by the pump. Subsequent to 940, 945, and 965 the method returns to start 905, incorporating a suitable delay (similar to that described above) to allow the effect of the decrease in fan or pump speed to have an effect on the temperature of the heat transfer fluid.

[0148] FIG. 10 is a flow diagram representing a method 1000 for control of the fuel cell systems described with reference to FIGS. 2.8, and allows the algorithm to adjust the Max AOGC T and Min AOGC T used in the method 900 of FIG. 9 to ensure adequate water recovery at the first heat exchanger 215 and in tank 220. Adequate water recovery means that the fuel cell system is self-sufficient for water by recovering water from the anode off gas to use in reforming (at a steam reformer or in the fuel cell stack) of fuel used at the anode.

[0149] The method 1000 starts at start 1005. The level of water in the tank 220 is monitored, and at 1010 it is identified that the level of water in the tank is low (e.g. below a threshold), therefore a greater rate of water recovery from anode off-gas is required. If the level of water in the tank is low, then at 1015 it is determined whether the AOG condensing temperature (T.sub.B) is less than the Max AOGC T. If, at 1015, the AOG condensing temperature (T.sub.B) is not less than the Max AOGC T, then it is assumed that the method 900 is acting to decrease the AOG condensing temperature (T.sub.B) and the method returns to start 1005, and in doing so a greater rate of water recovery from anode off-gas will be achieved. If, at 1015, the AOG condensing temperature (T.sub.B) is less than the Max AOGC T, then the method proceeds to reduce, at 1020, the Max AOGC T. The reduced Max AOGC T is used in the method 900, and as a result of reducing the Max AOGC T it is expected that, on average, the temperature of the heat transfer fluid is reduced, thereby increasing the rate of water recovery from anode off-gas and increasing the level of water in the tank 220. Subsequent to 1020 the method returns to start 1005, incorporating a suitable delay (similar to that described above) to allow the effect of the reduced Max AOGC T to have an effect on rate of water recovery from anode off-gas to the tank 220.

[0150] Returning to start 1005, the method 1000 also monitors the length of time that the system continually operates with the AOG condensing temperature (T.sub.B) at or within a threshold temperature of the Min AOGC T. The threshold temperature may be 30, 20, 10, or 5 deg C. depending upon wider system requirements and installation. If the length of time that the system continually operates with the AOG condensing temperature (T.sub.B) at (or within a threshold temperature of) the Min AOGC T exceeds a threshold period of time, then this is identified at 1025. The threshold period of time (“X” in FIG. 10) may be set at between 10 and 100 hours. Operation close to the Min AOGC T for long periods of time may lead to coking in components through which the dry anode off-gas passes. As a result, it is determined at 1030 whether the AOG condensing temperature (T.sub.B) remains within a threshold temperature of the Min AOGC T. If, at 1030, the AOG condensing temperature (Ta) is greater than the Min AOGC T plus the threshold temperature, then the method returns to start 1005 and the length of time that the system continually operates with the AOG condensing temperature (T.sub.B) at (or within a threshold temperature of) the Min AOGC T is reset. If, at 1030, the AOG condensing temperature (T.sub.B) is greater than the Min AOGC T plus the threshold temperature, then the method continues to 1035 where the Min AOGC T is increased. The increased Max AOGC T is used in the method 900. As a result, method 900 will tend to increase the temperature of the heat transfer fluid, thereby reducing the likelihood of coking in the system components through which the dry anode off-gas passes. Subsequent to 1035 the method returns to start 1005, incorporating a suitable delay (similar to that described above) to allow the effect of the increased Min AOGC T to have an effect on the temperature of the heat transfer fluid, thereby reducing the likelihood of coking in the system components through which the dry anode off-gas passes.

[0151] In an example, the desired AOG condensing temperature (T.sub.B) may be 50 deg C. for a particular system (based on the balance between sufficient water recovery and coking). The Min AOGC T may be set to 20 deg C., the threshold temperature to 30 deg C., and the threshold period of time to 24 hours. This means that the system may operate at T3<Min AOGC T+Threshold for up to 24 hours, which is expected to cause little coking, before Min AOGC T is increased to reduce water recovery and likelihood of coking.

[0152] It will be noted that method 1000 is a partial control logic as it shows only reducing Max AOGC T and increasing Min AOGC T. It will be understood that the Max AOGC T and Min AOGC T may be re-set to default values if the tank level is acceptable and the AOGC T is above the Min AOGC T. The re-set may occur immediately after start 1005 or otherwise periodically, for example every 10-100 hours.

[0153] The present invention is not limited to the above examples only, and other examples will be readily apparent to one of ordinary skill in the art without departing from the scope of the appended claims.