IMPROVED FUEL CELL SYSTEMS AND METHODS

Abstract

A fuel cell system comprising (i) at least one fuel cell stack (30) comprising at least one intermediate-temperature solid oxide fuel cell, and having an anode inlet (41) and a cathode inlet (61) and (ii) a reformer (70) for reforming a hydrocarbon fuel to a reformate, and a reformer heat exchanger (160); and defining: an anode inlet gas fluid flow path from a fuel source (90) to said reformer (70) to said fuel cell stack anode inlet (41); a cathode inlet gas fluid flow path from an oxidant inlet (140, 140′, 140″) through at least one cathode inlet gas heat exchanger (110, 150) to said reformer heat exchanger (160) to said fuel cell stack cathode inlet (61); wherein said at least one cathode inlet gas heat exchanger (110, 150) is arranged to heat relatively low temperature cathode inlet gas by transfer of heat from at least one of (i) an anode off-gas fluid flow path and (ii) a cathode off-gas fluid flow path; wherein said reformer heat exchanger is arranged for heating said anode inlet gas from said relatively high temperature cathode inlet gas to a temperature T.sub.3 at the anode inlet that is below a temperature T.sub.1 at the cathode inlet; and wherein oxidant flow control means (200) for controlled mixing of low temperature oxidant from the or each oxidant inlet (140, 140′, 140″) with high temperature cathode inlet gas to control a temperature T.sub.1 at the cathode inlet (61) relative to a temperature T.sub.3 at the anode inlet (41) and at a level higher than T.sub.3.

Claims

1. A fuel cell system comprising: (i) at least one fuel cell stack comprising at least one intermediate-temperature solid oxide fuel cell, and having an anode inlet, a cathode inlet, an anode off-gas outlet, and a cathode off-gas outlet; and (ii) a reformer, optionally a steam reformer, for reforming a hydrocarbon fuel to a reformate, and having a reformer inlet for anode inlet gas, a reformer outlet for exhausting anode inlet gas, and a reformer heat exchanger; and defining: (a) an anode inlet gas fluid flow path from a fuel source to said reformer to said at least one fuel cell stack anode inlet; (b) an anode off-gas fluid flow path from said at least one fuel cell stack anode off-gas outlet to a fuel cell system exhaust; (c) a cathode inlet gas fluid flow path from an at least one oxidant inlet through at least one cathode inlet gas heat exchanger to said reformer heat exchanger to said at least one fuel cell stack cathode inlet; and (d) a cathode off-gas fluid flow path from said at least one fuel cell stack cathode off-gas outlet to said fuel cell system exhaust; wherein said at least one cathode inlet gas heat exchanger is arranged to heat relatively low temperature cathode inlet gas by transfer of heat from at least one of (i) said anode off-gas fluid flow path and (ii) said cathode off-gas fluid flow path, to provide relatively high temperature cathode inlet gas; characterized in that said reformer heat exchanger is arranged for heating said anode inlet gas from said relatively high temperature cathode inlet gas to a temperature T.sub.3 at the anode inlet that is below a temperature T.sub.1 at the cathode inlet; and characterized by oxidant flow control means for controlled mixing of low temperature oxidant from the or each oxidant inlet with high temperature cathode inlet gas to control a temperature T.sub.1 at the cathode inlet relative to a temperature T.sub.3 at the anode inlet and at a level higher than T.sub.3.

2. The system according to claim 1, wherein the oxidant flow control means is arranged to control mixing of low temperature oxidant from an oxidant inlet at the cathode inlet so as to reduce the temperature T.sub.1.

3. The system according to claim 1, wherein the oxidant flow control means is arranged to control mixing of low temperature oxidant from an oxidant inlet at an input to the reformer heat exchanger so as to reduce the temperature T.sub.1 while also reducing the temperature T.sub.3.

4. The system according to claim 1, wherein the reformer heat exchanger comprises a hot bypass for cathode inlet gas to bypass the reformer heat exchanger and contribute to elevating said cathode inlet gas to temperature T.sub.1 at the cathode inlet.

5. The system according to claim 4, wherein the hot bypass comprises a pre-set aperture restrictor.

6. The system according to claim 4, wherein the hot bypass cathode inlet gas is drawn from the cathode inlet gas fluid flow path prior to mixing of low temperature oxidant.

7. The system according to claim 4, wherein the hot bypass comprises a controllable restrictor.

8. The system according to claim 1, wherein the oxidant flow control means is arranged to derive a reformer bypass air flow demand output signal from a reformer temperature input, which indicates fuel temperature at the reformer outlet, and a reformer setpoint input.

9. The system according to claim 8 further comprising a tail-gas burner in fluid flow communication with said at least one fuel cell stack anode and cathode off-gas outlets, having a tail-gas burner exhaust, defining a fluid flow path from said at least one fuel cell stack anode and cathode off-gas outlets to said tail-gas burner exhaust to said exhaust and further comprising a tail-gas burner exhaust temperature sensor for sensing a tail-gas burner exhaust temperature (T.sub.TGB), wherein said oxidant flow control means is further arranged to derive a tail gas burner exhaust temperature setpoint from the reformer temperature input and the reformer setpoint input.

10. The system according to claim 9 further comprising tail gas burner control means for providing a fuel demand actuator command derived from the tail gas burner exhaust temperature setpoint and the tail-gas burner exhaust temperature so as to increase supply of fuel to the tail gas burner when the tail-gas burner exhaust temperature is below the tail gas burner exhaust temperature setpoint as provided by the oxidant flow control means.

11. The system according to claim 1, comprising first and second oxidant mixers, the first mixer arranged for mixing low temperature oxidant from an oxidant inlet at an inlet to the reformer heat exchanger and the second mixer arranged for mixing low temperature oxidant from an oxidant inlet at a reformer heat exchanger outlet and cathode inlet.

12. The system according to claim 1, wherein the cathode inlet gas fluid flow path has a temperature of 750-850 degrees centigrade at its hottest point in steady state operation at ambient temperature air input.

13. The system according to claim 1, wherein T.sub.1 is controlled to be between 50 and 150 degrees centigrade higher than T.sub.3 in steady state operation at ambient temperature air input.

14. The system according to claim 1, wherein T.sub.1 is controlled to be between 500 and 600 degrees centigrade in steady state operation at ambient temperature air input.

15. The system according to claim 1, wherein T.sub.3 is controlled to be between 400 and 500 degrees centigrade in steady state operation at ambient temperature air input.

16. The system according to claim 1, wherein the reformer heat exchanger is a co-flow or parallel heat exchanger.

17. A method of operating a fuel cell having: (i) at least one fuel cell stack comprising at least one intermediate-temperature solid oxide fuel cell, and having an anode inlet, a cathode inlet, an anode off-gas outlet, and a cathode off-gas outlet; and (ii) a reformer for reforming a hydrocarbon fuel to a reformate, and having a reformer inlet for anode inlet gas, a reformer outlet for exhausting anode inlet gas, and a reformer heat exchanger; and defining: (a) an anode inlet gas fluid flow path from a fuel source to said reformer to said at least one fuel cell stack anode inlet; (b) an anode off-gas fluid flow path from said at least one fuel cell stack anode off-gas outlet to a fuel cell system exhaust; (c) a cathode inlet gas fluid flow path from an at least one oxidant inlet through at least one cathode inlet gas heat exchanger to said reformer heat exchanger to said at least one fuel cell stack cathode inlet; and (d) a cathode off-gas fluid flow path from said at least one fuel cell stack cathode off-gas outlet to said fuel cell system exhaust; the method comprising: heating relatively low temperature cathode inlet gas by heat exchange from at least one of (i) said anode off-gas fluid flow path and (ii) said cathode off-gas fluid flow path, to provide relatively high temperature cathode inlet gas; heating said anode inlet gas from said relatively high temperature cathode inlet gas to a temperature T.sub.3 at the anode inlet that is below a temperature T.sub.1 at the cathode inlet; and controlled mixing of low temperature oxidant from the or each oxidant inlet with high temperature cathode inlet gas to control, at a level higher than T.sub.3, the temperature T.sub.1 at the cathode inlet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG. 1 shows a schematic of a fuel cell system according to the prior art.

[0053] FIG. 2 is temperature sketch diagram illustrating temperature of air and fuel through the reformer of FIG. 1.

[0054] FIG. 3 is an alternative temperature sketch diagram illustrating temperature of air and fuel through the reformer of FIG. 1 in the case of post reformer air bypass.

[0055] FIG. 4 shows a schematic of a fuel cell system in accordance with a preferred embodiment of the present invention.

[0056] FIGS. 5 and 6 show temperature sketch diagrams illustrating temperature of air and fuel through the reformer of FIG. 4.

[0057] FIG. 7 illustrates control processes for controlling a fuel cell system in accordance with aspects of the invention.

[0058] FIG. 8 shows a schematic of an alternative fuel cell system in accordance with the present invention

[0059] FIG. 9 is a temperature sketch diagrams illustrating temperature of air and fuel through a reformer in accordance with an alternative embodiment of the invention.

[0060] For illustrative purposes only, the figures only indicate a single fuel cell. 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.

[0061] In the following embodiments, air is used as the oxidant. Any reference to “oxidant” elsewhere can therefore be construed as reference to “air” in the following embodiments, and vice versa.

DETAILED DESCRIPTION

[0062] Referring to FIG. 4, fuel cell system 400 is an intermediate-temperature solid oxide fuel cell (FT.sup.-- SOFC) system. Fuel cell stack 20 is a metal-supported IT-SOFC fuel cell stack. Fuel cell system 400 has a steady state 1 kW electric output from fuel cell stack 20, and comprises 121 metal-supported IT-SOFC fuel cells 30. Each fuel cell 30 has an anode side 40, electrolyte layer 50, and cathode side 60. 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 30 is to the full set of 121 fuel cells 30.

[0063] Electrical load L is placed across fuel cell 30.

[0064] Fuel cell stack anode inlet 41 is in fluid flow communication with fuel cell anode inlet 41 A for the flow of anode inlet gas to the anode side 40 of fuel cell 30. Fuel cell anode outlet 42A is in fluid flow communication with fuel cell stack anode off-gas outlet 42 for the flow of anode off-gas.

[0065] Fuel cell stack cathode inlet 61 is in fluid flow communication with fuel cell cathode inlet 61A for the flow of cathode inlet gas to the cathode side 60 of fuel cell 30. Fuel cell cathode outlet 62A is in fluid flow communication with fuel cell stack cathode off-gas outlet 62 for the flow of cathode off-gas.

[0066] Tail-gas burner 80 is in fluid flow communication with fuel cell stack anode and cathode off-gas outlets 42, 62 and has a tail gas burner exhaust 81, anode off-gas inlet 82 and cathode off-gas inlet 83. Tail-gas burner 80 defines a fluid flow path from fuel cell stack anode and cathode off-gas outlets 42, 62 to tail-gas burner exhaust 81, and is configured for burning anode and cathode off-gases and producing a tail-gas burner off-gas.

[0067] An anode inlet gas fluid flow path A is defined from fuel source 90 to evaporator 100 to steam reformer 70 to fuel cell stack anode inlet 41 to fuel cell anode inlet 41 A, i.e, the components are in fluid flow communication with one another.

[0068] An anode off-gas fluid flow path B is defined from fuel cell anode outlet 42A to fuel cell stack anode off-gas outlet 42 to anode off-gas heat exchanger 110 (HX-AOG) to condenser heat exchanger 120 to separator 130 to anode off-gas inlet 82 of tail-gas burner 80.

[0069] Main cathode inlet gas flow path 230 is defined from oxidant inlet 140 to blower 210 to anode off-gas heat exchanger 110 to air pre-heater heat exchanger 150 to reformer heat exchanger 160 to fuel cell stack cathode inlet 61 to fuel cell cathode inlet 61A. Air bypass inlet gas flow path 240 is defined from oxidant inlet 140′ to blower 210′ to air bypass inlet 190 to reformer heat exchanger 160 to fuel cell stack cathode inlet 61 to fuel cell cathode inlet 61A.

[0070] Air bypass inlet gas flow path 260 is defined from oxidant inlet 140″ to blower 210″ to air bypass inlet 190′ to fuel cell stack cathode inlet 61 to fuel cell cathode inlet 61A. Thus the air bypass inlet gas flow path 260 meets the cathode inlet gas fluid flow path (C) at air bypass inlet 190′ which is between the reformer heat exchanger 160 (and downstream of it) and the fuel cell stack cathode inlet 61, more particularly between the reformer heat exchanger oxidant outlet 162 and the fuel cell stack cathode inlet gas temperature sensor T1.

[0071] A cathode off-gas fluid flow path D is defined from fuel cell cathode outlet 62A to fuel cell stack cathode off-gas outlet 62 to cathode off-gas inlet 83 of tail-gas burner 80.

[0072] A tail-gas burner off-gas fluid flow path E is defined from tail gas burner exhaust 81 to air pre-heater heat exchanger 150 to evaporator heat exchanger 170 (HX-Evap) to fuel cell system exhaust 180. Anode off-gas heat exchanger 110 is in fluid flow communication with (i) fuel cell stack anode off-gas outlet 42 (i.e. with fuel cell anode outlet 42A) and tail-gas burner anode off-gas inlet 82, and (ii) oxidant inlet 140 and fuel cell stack cathode inlet 61 (i.e. with fuel cell cathode inlet 61A), and is arranged for exchanging heat between anode off-gas from fuel cell stack 20 and cathode inlet gas to fuel cell stack 20.

[0073] Air pre-heater heat exchanger 150 is in fluid flow communication with (i) tail-gas burner exhaust 81 and fuel cell system exhaust 180, and (ii) oxidant inlet 140 and fuel cell stack cathode inlet 61 (i.e. with fuel cell cathode inlet 61A), and is arranged for exchanging heat between tail-gas burner 81 off-gas and cathode inlet gas to fuel cell stack 20.

[0074] Reformer heat exchanger 160 may be a parallel-flow heat exchanger (other possibilities are described below) and is in fluid flow communication with (i) oxidant inlet 140 and fuel cell stack cathode inlet 61 (i.e. with fuel cell cathode inlet 61 A), and (ii) fuel source 90 and fuel cell stack anode inlet 41 (i.e. with fuel cell anode inlet 41A), and is arranged for exchanging heat between cathode inlet gas and anode inlet gas.

[0075] Evaporator 100 has a fuel inlet 101 for anode inlet gas from fuel source 90, a water inlet 102 for water from water supply 103, and an evaporator exhaust 104 of exhausting anode inlet gas from evaporator 100, and is located in the anode inlet gas fluid flow path between fuel source 90 and steam reformer 70. Evaporator 100 additionally comprises evaporator heat exchanger 170 located in the tail-gas burner off-gas fluid flow path E between air pre-heater heat exchanger 150 and fuel cell system exhaust 180.

[0076] Evaporator heat exchanger 170 is in fluid flow communication with (i) tail-gas burner exhaust 81 and fuel cell system exhaust 180, and (ii) fuel source 90 and water supply 103 and fuel cell stack anode inlet 41 (i.e. with fuel cell anode inlet 41 A), and is arranged to exchange heat between tail-gas burner off-gas and anode inlet gas and water, generating a steam fuel mix for the anode inlet gas to steam reformer 70.

[0077] Condenser heat exchanger 120 is in fluid flow communication with (i) fuel cell stack anode off-gas outlet 42 (i.e. fuel cell anode outlet 42A) and tail-gas burner anode off-gas inlet 82, and (ii) cooling circuit 121, and is arranged for exchanging heat between anode off-gas from fuel cell stack 20 and a cooling fluid in cooling circuit 121.

[0078] Separator 130 is located in the anode off-gas fluid flow path between condenser heat exchanger 120 and tail-gas burner 80, and has a separator condensate outlet 131, and is adapted to separate condensate from the anode off-gas fluid flow path, and exhaust the condensate via the condensate outlet 131.

[0079] Controller 402 has the same inputs and outputs as controller 200 of FIG. 1. It may be the same as controller 200 or may be modified vis-à-vis controller 200 as be described.

[0080] A hot cathode bypass 401 is provided, extending from the air outlet of air pre-heater heat exchanger 150 in path C direct to the anode inlet 61 of the fuel cell stack 20. This bypass allows a small amount of hot cathode inlet gas to bypass the reformer heat exchanger and contribute to elevating the cathode inlet gas to temperature at the cathode inlet. This bypass flow is small relative to the volume of cathode gas passing through heat exchanger 160.

[0081] Hot cathode bypass 401 preferably has a fixed restrictor or throttle 410. A variable throttle version is described further below.

[0082] The effect of hot cathode bypass 401 is illustrated in FIG. 5. It allows for heating of the air to a greater temperature than the fuel at the outlet of the reformer heat exchanger so that T1 at the cathode inlet is greater than T3 at the anode inlet. This allows for more internal reforming in the fuel cell stack 20 without drop in stack voltage. This in turn allows total airflow to be lower, which means lower power to the blower, which means higher overall system efficiency.

[0083] Providing reformer outlet temperature to be lower than stack air inlet temperature is found to give rise to more optimal system performance.

[0084] The temperature T1 of the cathode inlet 61A can be controlled by addition of cool air from air inlet 140″; through control of blower 210″.

[0085] This is illustrated in FIG. 6, in which the cathode inlet gas fluid temperature falls as it passes through reformer heat exchanger 160, then rises with the mixing of hot bypass gas from bypass 401 and then falls, in a controlled manner, upon the mixing of air from air inlet 140″.

[0086] Thus, as has been described, controller 402 can control the temperature T1 of the cathode inlet 61A by addition of cool air from air inlet 140″, through control of blower 210″, with the modification that this control takes place at a temperature above that fuel cell stack anode inlet 41.

[0087] Blowers 140 and 140′ may be replaced by a single blower and an adjustable valve/separator (not shown) that can adjust the proportion of inlet oxidant passing along, on the one hand, main cathode inlet gas fluid flow path 230 and, on the other hand, bypass inlet gas flow path 240.

[0088] FIG. 7 shows a modification to the control processes in controller 402 to achieve steady state operation of the apparatus of FIG. 4.

[0089] There is a reformer control process 700, a tail gas burner (TGB) process 701, a fuel control process 702 and an air control process 708.

[0090] The reformer control process takes as its inputs a reformer temperature 710 and a reformer temperature setpoint 711. The reformer temperature 710 is T3 measured at the reformer outlet 72 in FIGS. 1 and 4. The reformer control process delivers two outputs: a TGB output temperature setpoint 710 and a reformer bypass air flow demand 715.

[0091] The TGB control process 701 takes a TGB output temperature setpoint 710 as one of its inputs and a TGB outlet temperature 713 as another input and delivers a fuel demand output 714. The TGB outlet temperature is T.sub.TGB as measured at the TGB tailgas output 81 (FIGS. 1 and 4).

[0092] The fuel control process 702 takes the fuel demand output 714 as its input and converts this into an actuator control at its output to control supply of fresh fuel to the TGB from the fuel source 90 or 250 (FIG. 4) or fuel 82 that has passed through the reformer and stack, or a mixture of the two.

[0093] The air control process 708 takes the pre-reformer bypass air flow demand 715 as its input and converts this to an actuator control output 718. This control output controls valves 820 and 821 as well as blower 810. This is achieved in one of several alternative ways.

[0094] It may be desirable to keep either total airflow rate, main air flow rate or the post reformer bypass flow rate constant. For each of these cases more or less adjustment of the valve positions or blower speed will be required.

[0095] For example, it may be preferred to keep main air flow rate constant along path 230. In this case, valve 820 may be fixed and actuator control output 718 can control valve 821, with a corresponding adjustment to blower 810.

[0096] Alternatively, it may be preferred to keep post reformer bypass flow rate constant (along path 260) in which case, valve 821 may be fixed and actuator control output 718 can control valve 820, with a corresponding adjustment to blower 810.

[0097] Because of the difference in pressure drop in each of the flow paths it will generally be necessary to make some adjustment to both valves and blower.

[0098] FIG. 8. shows a fuel cell module as already described with reference to FIG. 4, in which like elements are given like reference numerals. There is a common cold air source 802, an air filter/noise attenuator 805, a fuel cell blower 810 and first and second air bypass valves 820 and 821. First air bypass valve 820 controls supply of cold air to the anode off-gas heat exchanger 110. Second air bypass valve 821 controls air to the air bypass inlet gas flow paths 240 and 260. These valves control the proportion of air passed from the blower 810 to these three paths.

[0099] Ambient air at about 30 Deg C. passes to the anode off-gas heater where is first heated and then to the air preheater 150 where it is further heated. This is the hottest point in cathode inlet gas fluid flow path C. Air is heated to a high temperature primarily by exhaust from the tail gas burner may be about 800 to 900 Deg C.

[0100] This hot air is mixed in mixer 830 with cold air from air bypass path 240. The outlet air from mixer 830 may be between 500 and 600 Deg C. This passes through the reformer heat exchanger, causing the reformed fuel to heat to between about 400 and 500 Deg C., and the air exits from the reformer heat exchanger at a similar temperature (or to a temperature about 15 to 25 Deg C. above that temperature, but, as will be explained, it may exit at a temperature below that of the reformed fuel).

[0101] Between the reformer heat exchanger oxidant outlet 162 and the fuel cell stack cathode inlet 61 is a further mixer 840 that has bypass paths 260 as an inlet and has hot bypass 401 as another inlet. Hot bypass path has a throttle, choke or restrictor 410.

[0102] After mixing with cold air from bypass path 260 and hot air from hot bypass 401, the temperature at the fuel cell stack cathode inlet 61 is between about 500 and about 600 Deg C. Thus, the temperature T1 at the fuel cell stack cathode inlet 61 is greater than the temperature T3 at the fuel cell stack anode inlet 41.

[0103] All the air from the blower 810 is used, so the blower is used to its maximum efficiency. The fuel cell stack cathode and anode inlet temperatures can be carefully controlled by air bypass valves 820 and 821 and the power supplied to the blower 810 can he reduced to match the demands from these valves.

[0104] In an alternative embodiment, the hot bypass 401 is dispensed with, and the reformer heat exchanger is modified to heat the fuel to a temperature below that of the oxidant from the cathode inlet gas fluid flow path, prior to mixing with air from air bypass inlet gas flow path 260. The reformer heat exchanger 160 can, for example, be a foreshortened parallel flow heat exchanger that does not completely heat the fuel to the outlet temperature of the air. Alternatively, it can be a contra-flow heat exchanger in which there is a temperature difference between the primary (heating) and secondary (heated) paths at all points along those paths. Other arrangements are possible. Operation of such embodiments is illustrated in FIG. 9, which shows the fuel and air emerging from the reformer heat exchanger with the air hotter than the fuel and shows a temperature drop as the emerging air is mixed in a controlled manner with oxidant from the cathode inlet gas fluid flow path, under the control of the blower 210″ (FIG. 4) or the bypass valve 821 (FIG. 8).

[0105] It has been explained that, in the preferred embodiment, the restrictor or throttle 410 is fixed. This is because controlling the flow of hot gas requires an expensive control valve that is prone to frequent maintenance or replacement. For this reason, in smaller systems, it is preferable to bring the temperature of the air exiting the reformer to a temperature above that of the fuel and then to cool it to the required temperature by mixing.

[0106] As an alternative, particularly in larger systems, the throttle 410 may be controlled by the controller 200 or 800 to allow just the required amount of hot cathode gas to bypass the reformer so as to bring the fuel cell stack cathode inlet 61 to the desired temperature above that of the fuel cell stack anode inlet 41. This arrangement may be preferable in systems generating more than 10 or 20 kW of power. In such systems, the energy saving from greater efficiency is such that the expense of hot flow control components may be outweighed by the energy savings.

[0107] In this way, a fuel cell system with a hot reformer bypass, and with cold pre- and post-reformer bypasses has been described and various alternative combinations of these (hot bypass with post-reformer bypass and no pre-reformer bypass; no hot bypass with post-reformer bypass and optional pre-reformer bypass; hot controllable bypass with post-reformer bypass and optional pre-reformer bypass). In some embodiments the fuel is heated in the reformer to a temperature below that of the oxidant at the reformer outlet. In the case, for example, of a counter flow reformer heat exchanger, the hot bypass flow would need to be greater, and the flow of cold pre ref bypass would be greater. These can indeed be advantageous in terms of lower pressure drops in the system or compactness.

[0108] System warm-up options may be provided in which a different type of reforming reaction is used other than steam reforming. For example, CPOX reforming can be used before reverting to SMR in normal operation. This would preferably include anode off gas recirculation. This would be implemented by taking some of the flow from stream ‘B’ at any point between the stack 20 and the TGB 80 and feeding it into the inlet of the reformer 70.

[0109] A related modification includes dispensing with the evaporator heat exchanger 170.

[0110] The present invention is not limited to the above embodiments only, and other embodiments will be readily apparent to one of ordinary skill in the art without departing from the scope of the appended claims.