GB2453997A

GB2453997A - Fuel Cell Stack And Reformer Arrangement

Info

Publication number: GB2453997A
Application number: GB0721003A
Authority: GB
Inventors: Paul Barnard; Bruce Girvan
Original assignee: Ceres Intellectual Property Co Ltd
Current assignee: Ceres Intellectual Property Co Ltd
Priority date: 2007-10-25
Filing date: 2007-10-25
Publication date: 2009-04-29
Anticipated expiration: 2027-10-25
Also published as: GB2453997B; GB0721003D0

Abstract

A fuel cell stack and reformer assembly is provided, for use in fuel cell stack system assemblies requiring a reformer to fully or partially reform inlet fuel, comprising a base plate 11; a fuel cell stack 19; a reformer unit 1 which comprises a reformer 2, a fuel steam mix inlet 14, a reformate chamber 30, and a reformate outlet 18a, wherein a wall of the reformate chamber 30 defines a heat exchange interface 17; and a fuel steam mixing chamber 10 having inlets for fuel and steam and an outlet arranged to feed into the fuel steam mix inlet 14 of the reformer. The fuel steam mixing chamber 10 is disposed between the base plate 11 and the reformate chamber 30 so as to act as a thermal break, and is in part defined by the heat exchange interface 17 so as to enable heat exchange between in-use reformate gas 15 in the reformate chamber and in-use fuel steam mix 9 in the fuel steam mixing chamber 10, in order to cool the reformate gas 15 to a temperature at or below the operating temperature of the fuel cell stack 19.

Description

-1 245399

FUEL CELL STACK AND REFORMER ARRANGEMENT

This invention relates to improved fuel cell stack and reformer arrangements, for use in fuel cell stack system assemblies requiring a reformer to fully or partially reform inlet fuel.

The term "fuel cell stack and reformer assembly" as used herein means an at least one fuel cell stack, each at least one fuel cell stack comprising at least one fuel cell stack layer, each at least one fuel cell stack layer comprising at least one fuel cell, fuel and oxidant inletloutlet connections, and flow paths for fuel and oxidant stream or streams, and for used fuel and oxidant stream or streams, a fuel cell stack base plate, a hood sealingly attached to the fuel cell stack base plate, and a reformer to fully or partially reform inlet fuel. Other optional components of a fuel cell stack assembly include a fuel side seal assembly, oxidant side seal assembly, end-plates and a compression system, fuel cell stack insulation, and electrical and control/monitoring connections as appropriate.

The term "fuel cell stack system assembly" as used herein means a fuel cell stack and reformer assembly together with system electronics and system control means. Other optional components include a water recovery system, a steam generator unit, an at least one heat exchanger optionally involving the phase change of one of the heat exchanger streams, thermal insulation, a start-up burner, and a fuel cell stack off-gas combustor.

The term "system electronics" includes the control electronics and/or any power electronics, where there can be at least one electronics board and/or unit optionally placed together or apart, in or close to the fuel cell stack assembly.

The term "system control means" includes the gas and fluid control valves and pumps, air blower unit, and safety equipment.

Fuel cell stack assemblies are operated taking inlet oxidant and fuel to generate oxidation products (herein referred to as exhaust gas streams, but also referred to as anode off-gas and cathode off-gas), heat, and electricity in the form of a DC current.

Overall, fuel cell stack system assemblies also comprise additional elements including system control means and system electronics including e.g. power electronics which transform the DC fuel cell output from a first voltage to a second voltage, and/or transform the DC fuel cell output into an AC wave form.

It is known in that fuel cells can operate on hydrogen, and that certain fuel cell technologies can additionally operate on reformed or semi-reformed hydrocarbon fuels.

Some of these later fuel cell technologies have operating temperatures that are different to that of the fuel reformer or pre-reformer.

For teelmo-economic and commercial reasons, it is desirable to have a fuel cell system that is efficient in operation and cost effective to purchase and run. For fuel cell systems where the fuel cell stack operates at intermediate and high temperatures, it is desirable to design the fuel cell stack and the various other hot components required to operate in a thermally integrated manner.

Metal supported intermediate temperature fuel cells that operate between 450 and 650°C have been developed. The system design for such an intermediate temperature fuel cell allows for full or partial reforming to occur to hydrocarbon fuels prior to the reformed fuel entering the fuel cell stack. Integration of the various components required to operate the fuel cell stack can reduce design complexity, reduce part count, improve the fuel cell system response and thermal efficiency, reduce costs and improve overall system operating efficiency.

Early system work involved a steam reformer as a separate unit to the fuel cell stack. A fuel cell module was designed to incorporate a fuel cell stack in a flow hood, both of which are mounted onto one side of a fuel cell stack base plate. The other hot components, such as the reformer and various heat exchangers were connected to the other side of the base plate, often using tubes. In this way the fuel cell stack base plate acted as a reference plate and a thermal zone boundary.

A steam reformer produces a reformate stream with a fluid temperature of around 700°C. This stream needs to be reduced in temperature before it enters into the fuel cell stack anode side. In the fuel cell stack, the reformate will be partially or fully depleted as it reacts across the fuel cell stack anode side. The reformate will also increase in temperature as it passes along the anode side due to the electrochemical reaction that occurs across the fuel cell anode-electrolyte-cathode, and due to the electrical resistance temperature release resulting from the current flowing through the fuel cell elements in the stack. It is therefore desirable to ensure that the reformate inlet stream temperature is less than or equal to the operating temperature of the fuel cell stack, by removing thermal energy from the reformate stream that leaves the reformer before the reformate stream enters the fuel cell stack. Accordingly, it is known to pass the refonnate stream through some form of heat exchanger between leaving the reformer and entering the fuel cell stack.

It would be desirable to be able to minimise the distance that the reformate has to travel between leaving the reformer and entering the fuel cell stack, so that any control of the reformer has a rapid response on the reaction in the fuel cell stack.

It is generally desirable in the manufacture of fuel cell modules to reduce the number of fluid connections to be made during assembly and to reduce packaging volume.

We have now found that it is possible to remove sufficient thermal energy from the reformate stream without compromising the temperature of either the fuel cell stack or the reformer unit, even though the fuel cell stack and the reformer operate at different temperatures, whilst minimising the reformate travel distance between the reformer and the fuel cell stack. Moreover, the fuel cell stack and reformer arrangement according to the present invention enables the reformer and the fuel cell stack to be better physically integrated around the fuel cell stack base plate and requires fewer fluid connections to be made during assembly of the fuel cell module. Thus, the arrangement according to the present invention enables a very compact and physically integrated assembly of a fuel cell stack, base plate and reformer unit, in which operation of the fuel cell stack is not compromised despite different operating temperatures between the fuel cell stack and reformer.

Accordingly, the present invention provides a fuel cell stack and reformer assembly, comprising: (i) a base plate; (ii) a fuel cell stack mounted on one side of the base plate, in which the fuel stack has a reformate inlet to the fuel cell stack; (iii) a reformer unit mounted on the other side of the base plate; in which the reformer unit comprises a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, and a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface; in which the base plate comprises a passage from its one side to its other side, connecting the refonnate chamber outlet of the reformer unit to the reformate inlet of the fuel cell stack; and (iv) a fuel steam mixing chamber having at least one inlet for fuel and steam and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer; in which the fuel steam mixing chamber is disposed between the base plate and the reformate chamber, and is in part defined by the heat exchange interface defined by the reformate chamber wall so as to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in the fuel steam mixing chamber.

According to the present invention there is also provided a method of feeding reformate to a fuel cell stack in a fuel cell stack system assembly, comprising: mixing fuel and steam to form a fuel steam mix flow; feeding the fuel steam mix flow between a base plate and a heat exchange interface so as to flow simultaneously over at least part of one side of the base plate and over one side of the heat exchange interface; reforming the fuel steam mix flow in a reformer to form a reformate flow; feeding the reform ate flow over the other side of the heat exchange interface to cool the reformate flow; feeding the cooled reformate flow through the base plate towards a fuel cell stack mounted on the other side of the base plate; wherein the heat exchange interface is disposed between the fuel steam mix flow and the reformate flow.

According to the present invention there is also provided a reformer unit comprising: a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface, and a fuel steam mixing chamber having at least one inlet and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer; in which the fuel steam mixing chamber is in part defined by the heat exchange interface defined by the reformate chamber wall so as to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in the fuel steam mixing chamber. Optionally, when the unit is mounted to a base plate, the fuel steam mixing chamber is further in part defined by the base plate.

According to the present invention there is also provided a reformer unit comprising: a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, and a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in a fuel steam mixing chamber, when the unit is mounted to a base plate having a fuel steam mixing chamber and having at least one inlet and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer, such that the fuel steam mixing chamber is in part defined by the heat exchange interface defined by the reformate chamber wall and optionally is further in part defined by the base plate.

The arrangement of the fuel steam mixing chamber in the assembly between the fuel cell stack base plate and the reformer enables the volume of fuel steam mix in the chamber to act as a thermal energy control device, by serving to function as a thermal break and to control the thermal energy transfer between the reformer and the fuel cell stack where the reformer and the fuel cell stack are connected to opposing sides of the fuel cell stack base plate. The fuel steam mixing chamber is preferably an integral part of either the reformer unit or the base plate, and is more preferably an integral part of the base plate.

The term ureformerlt as used herein includes any device used to fully or partially reform fuel, and may refer to a fully reforming device, or to a pre-reformer where additional reforming is to be carried out in the fuel call stack or in a further reforming device. The reformer in accordance with the present invention can use any suitable reformer technology such as steam reforming (SR), auto-thermal reforming (AIR) or catalytic partial oxidation (CPOX), and is preferably a steam reformer (SR). A steam reformer requires steam and fuel to be mixed prior to reacting over the steam reformer catalyst.

The reformer unit preferably includes a steam generator to generate a steam feed stream to the fuel steam mixing chamber or premixer.

The fuel may be entered into the fuel steam mixing chamber at a fluid temperature in the range of 0 to 120°C, preferably 20 to 80°C, more preferably 40 to 70°C.

The steam can be entered into the fuel steam mixing chamber at a fluid temperature in the range of 100 to 450°C, preferably 350 to 420°C.

The fuel steam mix at the point of inlet to the fuel steam mixing chamber suitably has a fluid temperature in the range of 200 to 350°C, preferably 200 to 350°C, and at the point of exit from the fuel steam mixing chamber suitably has a fluid temperature in the range of 350 to 550°C, preferably 400 to 500°C.

The reformate stream leaving the refonner catalyst area may have a fluid temperature in the range of 550 to 780°C, preferably 650 to 720°C, more preferably 670 to 700°C. The reformate stream at the point of exit from the reformate chamber may have a fluid temperature in the range of 500 to 600°C, and at the point of inlet to the fuel cell stack may have a fluid temperature in the range of 500 to 600°C.

In operation, the base plate temperature may be in the range of 400 to 650°C, preferably 450 to 550°C, more preferably 470 to 530°C. The air (oxidant) stream fed to the fuel cell stack may have a temperature in the range of 400 to 550°C, preferably 450 to 500°C.

The present invention is particularly applicable to solid oxide fuel cells (SOFCs), more particularly intermediate temperature solid oxide fuel cells (IT-SOFCs). Fuel cell stacks incorporating IT-SOFCs typically operate at around 450-650°C. The fuel cell stack base plate temperature is typically around 400-500°C when the fuel cell stack is operating.

The fuel cell base plate material can be selected from a range of metals, metal alloys, ceramics or cermets. Preferably it is selected from austenitic or ferritic stainless steels or nickel rich steels. Such steels can include stainless steels 310, 316, 321, Inconel 602, EU designation 1.4509 or JS3 (or commonly called Crofer 22APU produced by ThyssenKrupp). The preferred material for an IT-SOFC application is 3CR12. 3CR12 is a modification of grade 409 chromium stainless steel exhibiting good resistance to wet abrasion and mildly corrosive environments. National specifications covering this steel are 1.4003, TiNS S40977 / S41003. 3CR12 is a low cost, easily formed and durable steel with thermal expansion characteristics that are similar to those of the fuel cell stack and the reformer materials.

Forming of the base plate and the base plate features can occur by casting, machining or pressing (including pressing or injection of powder metals or cermets or ceramics in a mould). Presently the base plate is machined or cast, though the preference for high volume manufacture of the base plate is to cast.

Due to the corrosive environment that the fuel steam mixing chamber creates, it is important to select materials and material designs to protect the base plate material during all aspects of base plate forming and in-use operation. For this reason, a protective layer is desirable for at least the areas of the base plate that will be exposed to the fuel steam fluid and the reformate fluid. For casting, a cast liner protective layer may be used whereby, for instance, a metal or cermet or ceramic oxide protective layer, for example a cobalt or ceria oxide based protective layer, may be applied to the cast mould prior to pouring and forming of the base metal, for example 3CR 12. Preferably, a cobalt oxide based protective layer is applied to 3CR12 as base metal. The high temperature of the liquid metal will then sinter the protective layer material and thus form a protective layer that is physically integrated with the parent 3CR12 material. The mould may require a release layer to be applied to the mould material prior to applying the protective ceramic or metal oxide layer in order to facilitate removal of the casting from the mould. The protective layer can be provided over all or some of the surfaces of the base plate mould. The protective layers may be different for the fuel steam chamber and the reformate channel if the reformate channel is cast in the base plate.

Other methods of providing a protective layer include applying the protective layer after forming the base plate. Such methods include wash coating all or some of the formed base plate and then sintering the whole to form a suitable protective layer, or heating the base plate in a suitable environment to provide an oxide layer. Another method is to apply a thermal coating to the required areas requiring protection, such as an application process including plasma spraying.

The fuel cell stack is preferably a metal-supported IT-SOFC stack, more preferably as taught in US 6794075.

According to the present invention, the fuel steam mix chamber is so arranged that the fuel steam mix, typically having a temperature of between 100 and 450°C, provides the main thermal interface between the fuel cell base plate and the reformer. The lower temperature of the fuel and steam mix, and thus the mixing volume, protects the fuel cell base plate from gaining too much heat from the reformer and also acts as a heat sink to absorb heat from the reformate stream, thus reducing the temperature of the reformate stream before the reformate stream enters the fuel cell stack. The reformer can be mounted to the fuel cell stack base plate, and is preferably bolted to the base plate, with a gas-tight, deformable gasket placed between the reformer unit and the base plate such that the fuel steam mix and reformate cannot leak from the join between the reformer unit and base plate. Such a gasket can be, for instance, a vermiculite based compression seal gasket such as Thermiculite 866 (ex-Flexitallic) or a gas-tight deformable metal or alloy, or sandwich construction gasket, such as of the type commonly found in automotive exhaust applications.

The invention will be further apparent from the following description with reference to the several figures of the accompanying drawings which show, by way of example only, embodiments of assemblies in accordance with the present invention. Of the figures: Figure 1 shows a cut-away side view of a fuel cell stack and reformer assembly of the present invention, in which the fuel steam mixing chamber forms part of the fuel cell stack base plate and in which fuel and steam are fed to the fuel steam mixing chamber through separate feed pipes; Figure 2 shows an alternative fuel cell stack and reformer assembly, in which the fuel steam mixing chamber forms part of the fuel cell stack base plate as in Figure 1 but in which premixed fuel and steam are fed to the fuel steam mixing chamber from a fuel steam premixer; Figure 3 shows an alternative fuel cell stack and reformer assembly, in which the fuel steam mixing chamber forms part of the fuel cell stack base plate and in which premixed fuel and steam are fed to the fuel steam mixing chamber as in Figure 2, but in which a connecting conduit feeds the fuel steam mix from the fuel steam mixing chamber to the fuel steam feed annulus of the reformer unit and in which the reformate is fed to the fuel cell stack by a conduit through the fuel cell stack base plate; Figures 4a,b show an alternative fuel cell stack and reformer assembly, in which the fuel steam mixing chamber forms part of the reformer unit and in which premixed fuel and steam are fed to the fuel steam mixing chamber from a fuel steam premixer; Figures 5a,b show an alternative fuel cell stack and reformer assembly, in which the fuel steam mixing chamber forms part of the reformer unit as in Figure 4 but in which fuel and steam are fed to the fuel steam mixing chamber through separate feed pipes; Figures 6a,b show a cut-away side view of a reformer and fuel steam mixer assembly of the present invention, in which a fuel steam mixing chamber forms part of the reformer unit and in which fuel and steam are fed to the fuel steam mixing chamber through separate feed pipes; and Figure 7 shows an alternative reformer and fuel steam premixer assembly of the present invention, in which a fuel steam premixer forms part of the reformer unit, for use with a fuel cell stack and base plate assembly having a fuel steam mixing chamber that forms part of the fuel cell stack base plate.

Unless otherwise indicated, the features shown in Figures 2 to 7 are as shown in and described for Figure 1.

Teachings of fuel cell and fuel cell stack assemblies are well known to one of ordinary skill in the art, and in particular include US 6794075, WO 02/35628, WO 03/075382, WO 2004/089848, WO 2005/078843, WO 2006/079800, and WO 2006/106334, which are incorporated herein by reference in their entirety.

In embodiments shown in Figures 1 to 5b of a fuel cell stack and reformer assembly, a solid oxide fuel cell stack 19 is assembled from a number of fuel cell stack layers, with each fuel cell stack layer containing one or more fuel cells. Each fuel cell comprises an anode, electrolyte and cathode.

Fuel cell stack 19 is mounted on base plate 11 and a hood 21 is placed over fuel cell stack 19 and sealingly engages base plate 11 via gasket 20 to define a hood volume between base plate 11 and hood 21 and containing within it fuel cell stack 19.

Base plate 11 is provided with channels serving as air (oxidant) inlet 22 into the hood volume, cathode off-gas outlet 23 and anode off- gas outlet 24.

In use, reformate feeds to the anode electrode side of fuel stack via fuel inlet feed pipe I 8a or channel I 8b which passes through base plate 11.

In use, air (oxidant) enters the hood volume through oxidant inlet 22 and airflow occurs in the hood volume from oxidant inlet 22 along the sides of fuel cell stack 19 to fuel cell stack entry 25 at the cathode electrode side of fuel cell, and an electrochemical reaction takes place in which oxidant reacts with the cathode and fuel (reformate) reacts with the anode, heat, water and electrical energy being generated. The electrical energy passes across a load on an electrical circuit (not shown).

The reacted off-gases from the cathode and anode then exit fuel cell stack 19 by passing through base plate 11 via off-gas channels 23 and 24.

In the embodiments shown in Figures 1 to 7, a steam reformer unit I includes a steam generator 16. A water feed 3 enters via water feed pipe 4 into steam generator 16.

Generated steam 5 having a temperature of 100 to 400°C flows out of steam generator 16 via steam feed pipe 6. Fuel 7, for example at a temperature between 0 and 50°C, enters via fuel feed pipe 8 for mixing with generated steam 5. Steam reformer unit 1 is mounted to base plate 11 on the other side from that to which fuel stack 19 and hood 21 are mounted. Steam reformer unit 1 is mounted, e.g. by bolting, along peripheral mounting flange 13 via gasket 12.

In the embodiments shown in Figures 1, 5a, Sb, 6a and 6b, steam feed pipe 6 and fuel feed pipe 8 enter fuel steam mixing chamber 10 or 28 as separate feeds and form a mixture 9 of fuel and steam in fuel steam mixing chamber 10 or 28. In alternative embodiments shown in Figures 2, 3, 4a, 4b and 7, steam feed pipe 6 and fuel feed pipe 8 enter a premixer 26 as separate feeds and form a premixture of fuel and steam in premixer 26 before entering fuel steam mixing chamber 10 or 28 as a single premixed feed, for further mixing in fuel steam mixing chamber 10 or 28.

In the embodiments shown in Figures 1, 2, 3 and 7, fuel steam mix chamber 10 forms part of base plate 11. In alternative embodiments shown in Figures 4a, 4b, 5a, 5b, 6a and 6b, fuel steam mix chamber 28 forms part of reformer unit 1. When reformer unit I is mounted to base plate 11, a surface of base plate 11 forms a wall of fuel steam mix chamber 10 or 28 and thus defines part of fuel steam mixing chamber 10 or 28. An opposite wall of fuel steam mix chamber 10 or 28 is defined at least in part by heat exchange surface 17 of a heat exchanger whereby, in use, fuel steam mix 9 flowing through fuel steam mixing chamber passes between base plate 11 and heat exchange surface 17 before entering annular feed 14 to catalytic reformer 2, either directly as shown in Figures 1, 2, 4a, 4b, 5a, 5b, 6a and 6b, or via a connecting conduit 29 as shown in Figure 3. Thus, in use, flow of fuel steam mix 9 in fuel steam mixture chamber 10 or 28 serves to act as a thermal break for base plate 11, whilst simultaneously enabling heat exchange via heat exchange surface 17.

In the embodiments of Figures 4a, 5a and 6a, the wall of the fuel steam mix chamber 28 on the base plate side is defined by a sheet, e.g. of 3CR12 material, forming part of the reformer unit. Alternatively, as shown in the embodiments of Figures 4b, 5b and 6b, the side of the fuel steam mix chamber 28 on the base plate side is open before the reformer is mounted on the base plate, so as to become defined by the base plate when mounted thereto.

Fuel steam mix enter catalytic reformer 2 via annular feed 14 and is filly or partially reformed to generate reformate stream 15 having, for example, a temperature of around 700°C. Reformate 15 passes through reformate chamber 30 before entering fuel stack 19 via feed pipe l8a (Figures 1, 2, 4a, 4b, 5a and 5b) or feed channel 18b (Figure 3) through base plate 11.

Reformate chamber 30 has a wall defined at least in part by the above referred heat exchanger, whereby, in use, reformate 15 as it flows through reformate chamber 30 passes over a surface of the heat exchanger so as to enable heat exchange with relatively cooler fuel steam mix via heat exchange surface 17. Thus, heat can be sufficiently extracted from reformate stream 15 to reduce its temperature to or below the operating temperature of fuel cell stack 19, for example reduction from around 700°C to a temperature in the range of 450 to 550°C.

Figures 6a, 6b and 7 show embodiments of reformer units for mounting to base plate 11.

In the embodiments shown in Figures 6a and 6b, reformer unit 1 includes the volume of fuel steam mixture chamber 28 as an integral part, for mounting to a base plate 11 as depicted in Figures 5a and Sb. When thus mounted, fuel steam mix chamber 28 is in part constituted by a surface of base plate 11. In the embodiment shown in Figure 7, reformer unit I does not include the volume of a fuel steam mixture chamber and is for mounting to a base plate 11 that includes the volume of fuel steam mixture chamber 10 as depicted in Figure 2. When thus mounted, fuel steam mix chamber 10 is in part constituted by surface 17 of the heat exchanger of reformer unit 1.

It will be appreciated that it is not intended to limit the present invention to the above embodiments only, many other embodiments being readily apparent to a person of ordinary skill in the art without departing from the scope of the appended claims.

Reference numerals: I Combined steam reformer and steam generator unit 2 Steam reformer catalyst 3 Water feed 4 Water feed pipe Steam 6 Steam feed pipe 7 Fuel 8 Fuel feed pipe 9 Fuel steam mix Fuel cell base plate fuel steam mixing chamber 11 Fuel cell stack base plate 12 Gasket 13 Reformer unit mounting flange 14 Fuel steam feed annulus Reformate 16 *Steam generator 17 Reformate heat exchange surface 1 8a Reformate to fuel cell stack feed pipe 18b Reformate to fuel cell stack feed conduit 19 Fuel cell stack Gasket 21 Flow hood 22 Air 23 Cathode off-gas 24 Anode off-gas Air entry into stack 26 Fuel steam premixer 27 Fuel steam mix feed pipe 28 Reformer fuel steam mixing chamber 29 Fuel cell base plate fuel steam mixing chamber to fuel steam feed annulus conduit (hidden from view) Reformate chamber

Claims

CLAIMS: 1. A fuel cell stack and reformer assembly, comprising: (i) a base plate; (ii) a fuel cell stack mounted on one side of the base plate and having a reformate inlet to the fuel cell stack; (iii) a reformer unit mounted on the other side of the base plate; in which the reformer unit comprises a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, and a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface; in which the base plate comprises a passage from its one side to its other side, connecting the reformate chamber outlet of the reformer unit to the reformate inlet of the fuel cell stack; and (iv) a fuel steam mixing chamber having at least one inlet for fuel and steam and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer; in which the fuel steam mixing chamber is disposed between the base plate and the reformate chamber, and is in part defined by the heat exchange interface defined by the reformate chamber wall so as to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in the fuel steam mixing chamber.
2. A fuel cell stack and reformer assembly according to Claim 1, in which the reformer unit is bolted to the base plate with a gas sealing and thermally insulating gasket.
3. A fuel cell stack and reformer assembly according to Claim 1, in which the fuel steam mixing chamber has separate inlets for fuel and steam.
4. A fuel cell stack and reformer assembly according to Claim I in which the fuel steam mixing chamber has an inlet for premixed fuel and steam, and further comprising a fuel and steam premixer having separate inlets for fuel and steam.
5. A fuel cell stack and reformer assembly according to any of Claims 1 to 4, in which the fuel steam mixing chamber forms part of the base plate.
6. A fuel cell stack and reformer assembly according to Claim 5, comprising a conduit that connects the fuel steam mixing chamber outlet to the fuel steam mix inlet of the reformer.
7. A fuel cell stack and reformer assembly according to any of Claims 1 to 4, in which the fuel steam mixing chamber forms part of the reformer unit.
8. A fuel cell stack and reformer assembly according to any of the preceding claims, in which the fuel cell stack has an operating temperature of from 450 to 650°C.
9. A fuel cell stack and reformer assembly according to any of the preceding claims, in which the reformer has an operating temperature of from 650 to 720C.
10. A fuel cell stack and reformer assembly according to any of the preceding claims, in which the reformer unit further comprises a steam generator.
11. A fuel cell stack and reformer assembly according to any of the preceding claims, further comprising a flow hood over the fuel cell stack, arranged to direct oxidant flow over the fuel cell stack prior to entry into the fuel cell stack.
12. A method of feeding reformate to a fuel cell stack in a fuel cell stack system assembly, comprising: mixing fuel and steam to form a fuel steam mix flow; feeding the fuel steam mix flow between a base plate and a heat exchange interface so as to flow simultaneously over at least part of one side of the base plate and over one side of the heat exchange interface; reforming the fuel steam mix flow in a reformer to form a reformate flow; feeding the reformate flow over the other side of the heat exchange interface to coot the reformate flow; feeding the cooled reformate flow through the base plate towards a fuel cell stack mounted on the other side of the base plate; wherein the heat exchange interface is disposed between the fuel steam mix flow and the reformate flow.
13. A method according to Claim 12, in which the reformate flow has a temperature exceeding the operating temperature of the fuel cell stack and is cooled by heat exchange with the fuel steam mix flow to a temperature at or below the operating temperature of the fuel cell stack.
14. A method according to Claim 12 or Claim 13, in which separate streams of fuel and steam are mixed to form the fuel steam mix flow.
15. A method according to Claim 12 or Claim 13, in which separate streams of fuel and steam are premixed in a premixer to form the fuel steam mix flow.
16. A method according to any of Claims 12 to 15, in which the fuel steam mix flow is fed through a fuel steam mixing chamber that forms part of the base plate.
17. A method according to any of Claims 12 to 15, in which the fuel steam mix flow is fed through a fuel steam mixing chamber that forms part of a reformer unit that contains the reformer.
18. A method according to any of Claims 12 to 17, in which the reformate flow has a temperature of from 650 to 720CC.
19. A method according to any of Claims 12 to 18, in which the cooled reformate flow has a temperature of from 500 to 6O0C.
20. A reformer unit comprising: a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface, and a fuel steam mixing chamber having at least one inlet and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer; in which the fuel steam mixing chamber is in part defined by the heat exchange interface defined by the reformate chamber wall so as to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in the fuel steam mixing chamber.
21. A reformer unit comprising: a reformer, a fuel steam mix inlet to the reformer, a reformate chamber downstream of the reformer, and a reformate outlet from the reformate chamber, wherein at least a part of a wall of the reformate chamber defines a heat exchange interface to enable heat exchange between in-use reformate gas in the reformate chamber and in-use fuel steam mix in a fuel steam mixing chamber, when the unit is mounted to a base plate having a fuel steam mixing chamber and having at least one inlet and an outlet, the outlet being arranged to feed into the fuel steam mix inlet of the reformer, such that the fuel steam mixing chamber is in part defined by the heat exchange interface defined by the reformate chamber wall is further in part defined by the base plate.
22. A reformer unit according to Claim 20, in which, when the unit is mounted to a base plate, the fuel steam mixing chamber is further in part defined by the base plate.
23. A reformer unit according to any of Claims 20 to 22, further comprising a steam generator.
24. A reformer unit according to Claim 23 further comprising separate inlets for fuel and steam into the fuel steam mixing chamber.
25. A reformer unit according to Claim 23 further comprising a fuel and steam premixer having separate inlets for fuel and steam into the fuel steam mixing chamber.