WO2011015840A1

WO2011015840A1 - Cell stack system block

Info

Publication number: WO2011015840A1
Application number: PCT/GB2010/051149
Authority: WO
Inventors: Andreas Karl Backstrom; James Alexander Austin; Roger Anthony Pitts
Original assignee: Afc Energy Plc
Priority date: 2009-08-07
Filing date: 2010-07-14
Publication date: 2011-02-10
Also published as: GB0913827D0; GB2484242A; TW201117460A; GB201201383D0

Abstract

A system block (10) for mounting one or more cell stacks consists of two opposed half-blocks (12, 14) between which is sandwiched at least one separation plate (16). Each half-block (12, 14) comprises a flat plate and a multiplicity of protruding ribs. The ribs may be formed by injection moulding. The protruding ribs on an inner surface, that is a surface that faces the separation plate, define flow channels for fluids, while protruding ribs (20) on an opposite, outer surface of a half-block (12) define locating recesses or sockets for connection to cell stacks or to fluid flow ducts. At least some of the flow channels communicate with apertures in the flat plate of the half-block or apertures in the separation plate (16), and the cell stacks communicate with some of these apertures. The system block (10) enables fluids such as liquid electrolyte, hydrogen and air, to be supplied to and removed from one or more fuel cell stacks, while only requiring a single external connection for each fluid to or from the system block.

Description

Cell Stack System Block

The present invention relates to a system block for mounting one or more cell stacks, whereby fluids can flow to or from the cell stacks.

Background to the invention

Fuel cells have been identified as a relatively clean and efficient source of electrical power. Alkaline fuel cells are of particular interest because they operate at relatively low temperatures, are efficient and suitable for operation in an industrial environment.

Acid fuel cells and fuel cells employing other aqueous electrolytes are also of interest. Such fuel cells typically comprise an electrolyte chamber separated from a fuel gas chamber (containing a fuel gas, typically hydrogen) and a further gas chamber (containing an oxidant gas, usually air) . The electrolyte chamber is separated from the gas chambers using electrodes.

Typical electrodes for alkaline fuel cells comprise a conductive metal mesh, typically nickel, that provides mechanical strength to the electrode. Onto the metal mesh is deposited a catalyst which may for example contain activated carbon and a catalyst metal such as platinum. A single fuel cell does not produce a large voltage, and it is usually desirable to assemble a number of fuel cells into a stack to provide a larger electrical power output. For some purposes it may be necessary to assemble a number of such stacks, to provide still greater

electrical power output; and in this context there is a problem of providing the requisite fluids (electrolyte and gases) to each of the stacks. Discussion of the invention

The system block of the present invention addresses or mitigates one or more problems of the prior art.

There is provided in accordance with the present invention a system block for mounting one or more cell stacks, the system block comprising two opposed half- blocks between which is sandwiched at least one

separation plate; each half-block comprising a flat plate and a multiplicity of protruding ribs such that the half- block may be formed by injection moulding, wherein each half-block defines protruding ribs on an inner surface to define flow channels for fluids, the inner surface facing the separation plate, at least some of the flow channels communicating with one or more apertures in the flat plate of the half-block or one or more apertures in the separation plate, wherein one or more cell stacks may be mounted at an outer surface of at least one of the half- blocks to communicate with apertures therein.

Thus the system block enables fluids to be supplied to and removed from one or more cell stacks, while only requiring a single external connection for each fluid to or from the system block. This considerably simplifies the pipework for connecting the fluid ducts to all of the cell stacks, as the complexity involved in ensuring uniform distribution of the fluids is provided within the system block, and significantly reduces the part count.

Preferably at least one of the half-blocks also defines protruding ribs on an opposite, outer surface of the half-block to define locating recesses or sockets for connection to cell stacks or to fluid flow ducts.

Preferably each half-block defines protruding ribs on both surfaces, and preferably the half-blocks are each arranged to carry one or more cell stacks. In this case preferably at least some of the fluid flow apertures that communicate with cell stacks on opposite half-blocks are aligned with each other.

A system block can be arranged to define flow channels for liquid electrolyte, for a fuel gas (such as hydrogen) and for an oxidising gas such as oxygen, or another oxygen-containing gas such as air. In a

preferred embodiment the protruding ribs on the inner surface of any one half-block are of uniform height, those on the first half-block being of less height than those on the second half-block. The protruding ribs on the inner surface of the first half-block may define fluid flow channels for a liquid electrolyte, while the protruding ribs on the inner surface of the second half- block define fluid flow channels for a gas which are of larger cross-sectional area. The system block is particularly suited to fuel cell stacks, but it may also be utilised with electrolysis cell stacks, for example for electrolysis of water to generate hydrogen and oxygen. Preferably the system block also incorporates a tank for a liquid electrolyte.

The invention will now be further and more

particularly described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a system block of the invention, with the components separated for clarity; Figure 2a shows a plan view of an outer face of a first half-block of the system block of figure 1 (in the direction of arrow 2a of figure 2b) ;

Figure 2b shows a side elevation, in the direction of arrow 2b of figure 2a, of the half-block of figure 2a;

Figure 2c shows a plan view of the inner face of the half-block of figure 2a, being the view in the direction of arrow 2c of figure 2b; Figure 3a shows a plan view of an outer face of a second half-block of the system block of figure 1 (in the direction of arrow 3a of figure 3b) ;

Figure 3b shows a side elevation, in the direction of arrow 3b of figure 3a, of the half-block of figure 3a;

Figure 3c shows a plan view of the inner face of the half-block of figure 3a, being the view in the direction of arrow 2c of figure 3b;

Figure 4 shows a plan view of a perforated plate forming part of the system block of the invention.

A fuel cell consists of two electrodes, an anode and a cathode, separated by an electrolyte, and each

electrode is in contact with a respective gas stream. Chemical reactions that take place at the electrodes cause ions to migrate through the electrolyte, and generate an electric current in an external circuit. It is customary to arrange fuel cells in stacks, to obtain a larger voltage or power output than is available from a single fuel cell. Each such fuel cell stack must be supplied with appropriate fluids. For example the electrolyte may be an aqueous solution of potassium hydroxide (KOH) , and the gas streams may be hydrogen and air or oxygen. In the example described below a KOH electrolyte and an air stream are passed in parallel through the fuel cell stacks, while a hydrogen stream is passed through them in series. Referring now to figure 1, a system block 10 of the invention consists of a first half-block 12, a second half-block 14, and a perforated plate 16. In addition the system block 10 includes a generally rectangular tank 18 with an open end surrounded by a peripheral flange 19. When assembled, the perforated plate 16 is sandwiched between, and bonded to, the inner faces of the first half-block 12 and the second half-block 14. The outer faces of the first and second half-blocks 12 and 14 have projecting ribs that define two generally rectangular recesses 20 within which are several projecting sockets 22 (described in greater detail below) . In use a fuel cell stack (not shown) is inserted into each such

rectangular recess 20, and the sockets 22 provide for flow of fluids to and from each fuel cell stack. Hence in this example the system block 10 would carry four fuel cell stacks, two on each side.

Referring now to figure 2a the first half-block 12, on its outer face, also defines a large rectangular aperture 24 through which the rectangular tank 18

projects. It also defines two spaced apart circular apertures 25 and 26 between which is connected an air scrubber (not shown) . Referring now to figure 2c, the first half-block 12, on its inner face, defines several projecting ribs arranged to define (along with the adjacent perforated plate 16) a number of fluid flow channels .

Referring now to figure 3a the second half-block 14, on its outer face, also defines a large circular aperture 25b which is connected to an air blower (not shown) ; two sockets 33 and 34 between which is connected an

electrolyte pump (not shown); and two sockets 36 and 37 for a hydrogen supply (as described later) . Referring to figure 3c, the second half-block 14, on its inner face, defines several projecting ribs arranged to define (along with the adjacent perforated plate 16) a number of fluid flow channels. It will be appreciated that as regards each of the half-blocks 12 and 14, the projecting ribs on both surfaces extend at right angles to the surface, so that each half-block can be made by injection moulding from a plastics material, such as ABS (acrylonitrile butadiene styrene) . The ribs on any one half-block 12 or 14 are of uniform height, but the ribs on the first half block 12 are shorter than those on the second half-block 14. As described more fully below, the electrolyte flow channels are defined in the first half-block 12, while the air flow channels, which are of larger cross-section, are defined in the second half-block 14. In use the tank 18 contains electrolyte, aqueous potassium hydroxide (KOH) in this example. The open face of the tank 18 is sealed around the flange 19 onto the perforated plate 16. The KOH can flow out of the tank 18 through the hole 33a in the plate 16 and hence through the socket 33 in the second half-block 14 to the

electrolyte pump. The electrolyte is then pumped back through the socket 34 in the second half-block 14 into the diagonal flow channel 40. At the other end of the flow channel 40 the electrolyte passes through a hole 41 and into the bottom of a generally T-shaped flow channel 42 in the first half-block 12. The flow splits along the two branches of the T-shaped flow channel 42, and is thereby distributed through eight holes 43 into the fuel cell stacks mounted on the first half-block 12. The electrolyte also flows through eight holes 43a in the plate 16 (that are aligned with the holes 43) and hence through aligned holes 43b in the second half-block 14 to supply the fuel cells mounted on the second half-block 14. The electrolyte emerges from the top of each fuel cell stack to flow through holes 44 (in the first half- block 12), or through aligned holes 44b in the second half-block 14 and 44a in the plate 16, so that the electrolyte from all the fuel cell stacks flows into the top of a tree-shaped flow channel 45 in the first half- block 12. The electrolyte flows along this tree-shaped flow channel 45, and at the bottom emerges through a hole 46 in the plate 16, into a diagonal flow channel 47 in the second half-block 14. It then emerges through a hole 48 in the plate 16 into the tank 18.

The air provided by the air blower flows through the aperture 25b in the second half-block 14, and through an aligned aperture 25a in the plate 16 to the aperture 25 in the first half-block 12, and hence through the air scrubber, which removes any carbon dioxide from the air.

The scrubbed air stream passes through the aperture 26 and an aligned aperture 26a in the plate 16, and so into a large flow channel 50 on the second half-block 14. The flow channel 50 splits into two, and each half then splits into three, leading to holes 52 that feed into the fuel cell stacks mounted on the second half-block 14. There are also aligned holes 52a through the plate 16 and aligned holes 52b through the first half-block 12, so that the air supply is also fed into the fuel cell stacks mounted on the first half-block 12.

The air emerging from the fuel cell stacks flows through holes 53 (in the second half-block 14), or through aligned holes 53b in the first half-block 12 and 53a in the plate 16, so that the air from all the fuel cell stacks flows into a channel 55 in the second half- block 14. The channel 55 communicates through a small aperture 56 in the plate 16 with an air space above the electrolyte in the tank 18; the air from that air space then flows out through an aperture 57 through the plate 16 into an exhaust channel 58 in the second half-block 14, leading to an outlet exhaust port 59 at the top of the second half-block 14, through which the air exhausted from the cell stacks is vented to the atmosphere.

Hydrogen is supplied through the inlet port 36 on the second half-block 14, to flow through an aligned hole 36a through the plate 16 and into the bottom of a narrow flow channel 62 in the first half-block 12. The hydrogen therefore flows up and down to reach two outlet holes 63 that feed the hydrogen into a fuel cell stack. The outflowing hydrogen from that fuel cell stack emerges through holes 64 to flow along two parallel channels 65 in the first half-block 12, and then through holes 66 to feed into the other fuel cell stack mounted on the first half-block 12. The out-flowing hydrogen from that other fuel cell stack then emerges through holes 67, to pass through aligned holes 67a in the plate 16 and 67b in the second half-block 14, which feed the hydrogen into a first one of the fuel cell stacks mounted on the second half-block 14 (which is hence the third fuel stack, as regards the hydrogen flow) .

The out flowing hydrogen from the third fuel stack emerges through two holes 68 to flow through two parallel channels 69 in the second half-block 14 leading to two holes 70 that feed the hydrogen into the fourth fuel cell stack. The hydrogen outflow from the fourth fuel cell stack emerges through holes 72 that communicate with a flow channel 74 in the second half-block 14, so the gas flows up and down to reach the outlet port 37. In normal operation there is no through flow of hydrogen, for most of the time, as the hydrogen is consumed as it flows through the fuel cell stacks. Occasionally it may be necessary to clear any contaminant gases from the

hydrogen chambers of the fuel cell stacks, and this may be achieved by opening a valve (not shown) connected to the outlet port 37, so that there is a through flow of hydrogen to flush out any contaminants. Furthermore the flow direction of hydrogen may be reversed, by supplying the hydrogen to the outlet port 37 so that it would flow through the fuel cell stacks in the reverse direction, ending up at the inlet port 36.

When clearing contaminants gases from the hydrogen chambers, the out flowing gas stream containing hydrogen and the contaminants emerging from the outlet port 37 (or from the inlet port 36, if the flow direction is

reversed) is fed through a purging port 76 in the second half-block 14. Any electrolyte carried by the gas stream is de-entrained as it impacts with the ribs, and flows down a return passage 77 to flow through a drainage port 78 through the plate 16 back into the tank 18. The gas phase passes upwardly through notches in the ribs to emerge through an outlet port 79.

When starting up the fuel cell stacks, or when terminating their operation, it may be desirable to flow an inert gas such as nitrogen through the channels that would normally carry hydrogen.

In this example each fuel cell stack is enclosed within a box that seals to the corresponding recess 20 in the half-block 12 or 14. The space within that box communicates with five ports 80 in the respective half- block 12, 14, through which any gases leaking from the fuel cell stack will therefore pass, reaching the space within the support block 10. The gases can then flow through notches 81 in the ribs and through holes 82 in the plate 16 to the vicinity of a hydrogen sensor 84. This is a safety device, so that if any such leakage occurs the system can be shut down.

The space within each enclosing box also

communicates with a drainage port 86 near the bottom of the corresponding recess 20, to allow for any leaking electrolyte. Considering the first half-block 12, as shown in figure 2c each drainage hole 86 communicates with a generally rectangular space defined by the ribs, from which the electrolyte can pass through a drainage hole 87 in the plate 16. As regards the second half- block 14, as shown in figure 3c each drainage hole 86 communicates with a space defined by the ribs, and the electrolyte passing through the drainage holes 87 communicates with these same spaces. The electrolyte can then flow down paths defined by notches 88 in the ribs, to end up in a rectangular sump chamber 90. An outlet from this sump chamber 90 is closed by a removable stopper 92.

The component parts shown in figure 1 are friction welded together to ensure that they are welded together wherever a rib meets the plate 16, and are also secured together using several bolts 85. In a modification there are two identical thin plates 16, and one plate is laser welded (welding through the thickness of the plate) onto the second half-block 14; and the tank and the other plate 16 are laser welded onto the first half-block 12, again ensuring in each case that they are welded together wherever a rib meets one of the plates 16. The two plates 16 are then fixed together using adhesive covering the entire surface apart from the holes. And again the component parts are also preferably secured together using bolts 85.

It will be appreciated that the system block 10 described above may be modified while remaining within the scope of the present invention, which is as defined in the claims. For example the arrangement of the ribs may differ from that shown in the figures.

The system block 10 thus provides a convenient way of supplying all the required fluids - electrolyte, hydrogen and air - to a number of fuel cell stacks.

Since each fuel cell stack can readily be connected to the sockets 22 in the respective recess 20, no pipes have to be connected to individual fuel cell stacks. And the other components required for operation, such as the air blower, the air scrubber, and the electrolyte pump, can readily be attached to or integrated into the system block 10. In the system block 10 described above, fuel cell stacks are mounted on both sides of the system block 10, two on each side. In a modification, a system block might instead be designed to accommodate only two fuel cell stacks, either one on each side, or two on one side and none on the other. The system block 10 described above is for use with fuel cell stacks in which the electrolyte is aqueous potassium hydroxide solution, but it will be appreciated that the system block 10 might instead be used with fuel cell stacks using a different liquid electrolyte. In the system block 10 described above, the protruding ribs defining flow channels on the first half-block 12 are less high than the protruding ribs that define flow channels on the second half-block 14, but in a modification the protruding ribs defining flow channels may be of equal height on both the first and the second half blocks. Furthermore a system block of the invention may be designed to supply appropriate fluids to a different type of fuel cell stack, for example a polymer electrolyte fuel cell stack. It will also be appreciated that the system block 10 may be used with electrolysis cell stacks, or with flow batteries .

Claims

1. A system block for mounting one or more cell stacks, the system block comprising two opposed half-blocks between which is sandwiched at least one separation plate; each half-block comprising a flat plate and a multiplicity of protruding ribs such that the half-block may be formed by injection moulding, wherein each half- block defines protruding ribs on an inner surface to define flow channels for fluids, the inner surface facing the separation plate, at least some of the flow channels communicating with one or more apertures in the flat plate of the half-block or one or more apertures in the separation plate, wherein one or more cell stacks may be mounted at an outer surface of at least one of the half- blocks to communicate with apertures therein.

2. A system block as claimed in claims 1 wherein at least one of the half-blocks also defines protruding ribs on an opposite, outer surface of the half-block, the protruding ribs on the outer surface defining locating recesses or sockets for connection to cell stacks or to fluid flow ducts.

3. A system block as claimed in claim 2 wherein each half-block defines protruding ribs on both surfaces.

4. A system block as claimed in claim 3 wherein each half-block is arranged to locate one or more cell stacks.

5. A system block as claimed in claim 3 or claim 4 wherein at least some of the apertures to provide fluid flow to or from cell stacks on opposite half-blocks are aligned with each other, and are aligned with

corresponding apertures in the separation plate.

6. A system block as claimed in any one of the preceding claims wherein the protruding ribs on the inner surface of any one half-block are of uniform height, those on the first half-block being of less height than the those on the second half-block.

7. A system block as claimed in claim 6 wherein the protruding ribs on the inner surface of the first half- block define fluid flow channels for a liquid

electrolyte, while the protruding ribs on the inner surface of the second half-block define fluid flow channels for a gas.

8. A system block as claimed in claim 7 wherein the protruding ribs on the inner surface of the second half- block define fluid flow channels for air.

9. A system block as claimed in any one of the preceding claims wherein the flow channels for fluids include flow channels for liquid electrolyte, for fuel gas, and for oxygen-containing gas.

10. A system block as claimed in claim 9 wherein the system block also comprises an electrolyte storage tank.

11. A system block as claimed in any one of the

preceding claims wherein each half-block on which a cell stack may be mounted also defines leak-flow apertures to allow any fluid leaking from the cell stack to flow into the system block.

12. A system block as claimed in claim 11 wherein each half-block on which a cell stack may be mounted defines at least one leak-flow aperture for gas and at least one leak-flow aperture for liquid, to allow any liquid electrolyte leaking from the cell stack and any gas leaking from the cell stack to flow into the system block .

13. A system block as claimed in claim 11 or claim 12 wherein the system block defines baffles arranged such that if any gas leaking from the cell stack flows into the system block, the baffles separate any liquid entrained in the leaking gas.