WO2014174299A1

WO2014174299A1 - A fuel cell system

Info

Publication number: WO2014174299A1
Application number: PCT/GB2014/051278
Authority: WO
Inventors: Christopher James GURNEY; Christopher Conlon; Philip SHARDLOW; Paul Leonard Adcock; Pratap RAMA; Jonathan Cole; Daniel NINAN
Original assignee: Intelligent Energy Limited
Priority date: 2013-04-24
Filing date: 2014-04-24
Publication date: 2014-10-30
Also published as: GB201307411D0; GB2515463A; GB2515463B

Abstract

A fuel cell system (100) comprising a fuel cell (102) having an exhaust (104), and a liquid separator (106). The liquid separator (106) comprising an inlet (108) coupled to the exhaust (104) of the fuel cell (102); an outlet (110); a drain (112); and a separation chamber (114) defining a fluid flow path between the inlet (108) and the outlet (110). The separation chamber (114) comprises a plurality of channel structures (116) each having an open channel face disposed towards the upstream direction of the fluid flow path and having a channel axis extending in a direction towards the drain (112).

Description

A Fuel Cell System

The present disclosure relates to fuel cell systems and, in particular, to fuel cell systems that have a water separator at an exhaust of a fuel cell.

According to a first aspect of the invention there is provided a fuel cell system comprising:

a fuel cell having an exhaust; and

a liquid separator comprising:

an inlet coupled to the exhaust of the fuel cell;

an outlet;

a drain; and

a separation chamber defining a fluid flow path between the inlet and the outlet,

wherein the separation chamber comprises a plurality of channel structures each having an open channel face disposed towards the upstream direction of the fluid flow path and having a channel axis extending in a direction towards the drain.

The fuel cell system may further comprise a cooling means configured to cool the plurality of channel structures. The cooling means may comprise a conduit passing through each of the plurality of channel structures. The conduit may be configured to receive a coolant.

The channel axis may extend towards the drain in a downward direction. The channel axis may extend in a direction that is transverse to the fluid flow path.

The channel structures may each comprise a C-shaped channel having two side walls and a base. The side walls of the C-shaped channel may be perpendicular to, or obliquely angled to, the base of the C-shaped channel.

The depth of the C-shaped channel may vary along the length of the channel. The channel structures may comprise a substantially planar region.

The plurality of channel structures may be disposed in a laterally and longitudinally extending array relative to the flow path. The plurality of channel structures may be each separated from one another by a lateral flow space and a longitudinal flow space. The lateral width of flow spaces between channel structures may vary as a function of distance from the inlet. The lateral width of the channel structures may vary as a function of distance from the inlet. The longitudinal depth of the channel structures may vary as a function of distance from the inlet. The number of channel structures in a lateral row of channel structures may vary as a function of distance from the inlet.

The open channel faces of the channel structures may comprise a hydrophobic region proximal to the drain and a hydrophilic region distal to the drain. The fuel cell system may comprise a plenum between the bottom of the channel structures and a bottom surface of the separation chamber, and optionally a first baffle plate located in the plenum. The first baffle plate may be in a plane transverse to the channel axis of the channel structure. The first baffle plate may extend over the majority, but not all, of the footprint of the separation chamber.

The fuel cell system may further comprise a second baffle plate provided in the flow path between the first baffle plate and the outlet. The second baffle plate may extend from the wall in which the outlet is provided at a position that is between the first baffle plate and the outlet.

The exhaust of the fuel cell may be a cathode exhaust. There may be provided a fluid processing component comprising:

a liquid separator comprising:

an inlet;

an outlet;

a drain; and

a separation chamber defining a fluid flow path between the inlet and the outlet, wherein the separation chamber comprises a plurality of channel structures each having an open channel face disposed towards the upstream direction of the fluid flow path and having a channel axis extending in a direction towards the drain; and

a cooling means configured to cool the plurality of channel structures.

A description is now given, by way of example only, with reference to the accompanying drawings, in which: figure 1a illustrates a fuel cell system;

figures 1 b and 1 c show further details of the water separator of figure 1 a;

figure 2 shows an illustration of example streamlines that demonstrate the flow path of air through the water separator of figures 1b and 1c;

figures 3a and 3b illustrate example geometries of channel structures that can be used in any of the water separators disclosed herein;

figure 4 illustrates a plan view of an array of channel structures;

figure 5 illustrates a water separator; and

figure 6 illustrates a channel structure that has a coolant conduit passing through it.

Figure 1 a illustrates a fuel cell system 100 that includes a fuel cell 102. The fuel cell 102 may comprise a single fuel cell or a fuel cell stack having a plurality of fuel cells. The fuel cell 102 has an exhaust 104, which may be an anode or cathode exhaust of the fuel cell 102.

The fuel cell system 100 also includes a liquid separator 106 having an inlet 108 coupled to the exhaust 104 of the fuel cell for receiving an exhaust fluid, an outlet 110 for ejecting gas from the exhaust fluid, and a drain 112 for ejecting liquid that has been separated out of the exhaust fluid. The liquid separator 106 may be used to remove water from a cathode exhaust fluid, and therefore will be referred to as a water separator 106 in this disclosure. The skilled person will appreciate however that the liquid separator 106 can be used to separate any liquid from any fluid that it receives. Figures 1 b and 1c show further details of the water separator 106 of figure 1 a. In this example, the inlet 108 and outlet 1 10 are on opposing side walls of the water separator 106 and the drain 112 is in a bottom wall of the water separator 106. The water separator 106 has a separation chamber 114 defining a fluid flow path between the inlet 108 and the outlet 110. The separation chamber 114 houses a plurality of channel structures 1 16 each having an open channel face 1 18 disposed towards the upstream direction of the fluid flow path and having a channel axis extending in a direction towards the drain 1 2. In this example, the channel axis is transverse or perpendicular to the fluid flow path. Although it will be appreciated that it could be obliquely disposed and still perform the required functionality of water separation.

The exhaust fluid received at the inlet 108, which may be referred to as a two phase mixture, hits the open channel faces 118 of the channel structures 116. In this example, the fluid flow path extends in a horizontal direction. Water droplets in the exhaust fluid coalesce on the walls, which can form a film that passes downwards along the channel structures 116 towards the drain 112. The channel axis is provided in a downward direction so that gravity can be used to move the separated water towards the drain 112. Air in the exhaust fluid is forced to weave through the channel structures 116 before leaving the water separator 106 through the outlet 110.

The water separation performed by the water separator 106 is based upon the concept of lowering the velocity of the flow of the exhaust fluid and increasing the surface contact area to drop out water. In some applications this can be preferred to using a cyclone to induce a high speed swirling flow to separate fluids of different densities. In particular, one or more of the water separators disclosed herein can advantageously:

• provide a low pressure drop between the inlet and the outlet, particularly for low energy exhaust fluid flow;

• reduce overall system volume as the water separator can be placed in the lines of existing system pipe work without taking up significant extra space;

• provide a low level of liquid re-entrainment into the gas that exits the water separator through the outlet;

· be conveniently located at bends in the system pipe work by using inlets or outlets that are shaped to redirect the fluid flow in the desired direction; and/or

• be easily scaled for different system requirements.

In the example of figures 1 b and 1 c, the bottom of the channel structures 116 are spaced apart from the bottom surface of the separation chamber 114, thereby defining a plenum at the bottom of the separation chamber. Located within the plenum is a first baffle plate 120 that is in a plane transverse or perpendicular to the channel axis of the channel structure 116. The first baffle plate 120 in this example is spaced apart from both the bottom of the channel structures 116 and the bottom surface of the separation chamber 114, thereby defining an upper region of the plenum 124 (closest to the channel structures 116) and a lower region of the plenum 126 (closest to the bottom surface of the separation chamber 114). In other examples the channel structures may extend to and abut the first baffle plate 120. The first baffle plate 120 in this example extends over the drain 112. The first baffle plate 120 extends over the majority, but not all, of the footprint of the separation chamber 114, for example at least 60%, 70%, 80%, 90% or 95%. In this way, an opening is provided between the upper and lower regions of the plenum 124, 126 through which fluids can pass. The opening is optionally defined between the first baffle plate 120 and a back wall 121 , which is the wall 121 in which the outlet 110 is provided. The specific dimensions of the first baffle plate can be optimised for any particular application.

In use, water drips from the bottom of the channel structures 116, through the upper region of the plenum 124, onto the first baffle plate 120. The water then flows over the surface of the first baffle plate 120 towards the opening to the lower region of the plenum 126 from where it can enter the drain 112. The air flow through the upper region of the plenum 124 can move the water towards the opening. In some examples, the first baffle plate 120 can be angled towards the opening in order to assist in moving the water in this direction. The lower region of the plenum 126 may be referred to as a water collection tank at the bottom of the water separator 106 from where it can be removed. In some examples, the lower region of the plenum 126 may be provided with a heater that can be used to melt any ice that may freeze in the bottom separation chamber when the fuel cell system is not in use.

The first baffle plate 120 is also used to redirect air in the separation chamber 114 towards the outlet 110, and reduce the likelihood that the air exits the water separator 106 through the drain 112.

In this example a second baffle plate 122 is provided in the air flow path between the first baffle plate 120 and the outlet 110. The second baffle plate 122 extends from the back wall 121 , in this example across the entire width of the separation chamber 114. The second baffle plate 122 is located at a height that is between the first baffle plate 120 and the outlet 110. The second baffle plate 122 can be considered as providing a step or lip in the back wall 121. Such a step can be useful because some exhaust fluid will impact on the back wall 121 , possibly having bypassed the channel structure 1 16. If this exhaust fluid contains water then it is possible that water will be deposited on the back wall 121. The second baffle plate 122 provides a barrier to water in the plenum 126 and also any water deposited on the back wall exiting the separation chamber 114 through the outlet 110, which is undesired.

Figure 2 shows an illustration of example streamlines that demonstrate the flow path of air through the water separator of figures 1b and 1c. The left-hand drawing in figure 2 shows a plan view of the water separator 206 and the right-hand drawing shows a side view. It can be seen from the right-hand drawing that only a modest amount of the air flows into the lower region of the plenum 226.

Figures 3a and 3b illustrate example geometries of channel structures that can be used in any of the water separators disclosed herein.

Figure 3a shows a first channel structure 340 with a C-shaped channel. In cross-section, the C-shaped channel can be considered as having two side walls 342 and a base 344. In this example, the two side walls 342 are perpendicular to the base 344. The inwardly facing surface of the base 344 is an example of open channel face of the first channel structure 340. In use, and as shown in figure 2, exhaust fluid impacts on the open channel face 344. Water in the exhaust fluid coalesces on the open channel face 344 and air either flows back on itself so that it can continue towards the outlet around the side walls 342 of the first channel structure 340 or it flows downwards towards the plenum below the channel first structure 340.

Figure 3a also shows a second channel structure 346 in which the depth of the channel varies along the length of the second channel structure 346. In this example, no side walls of the second channel structure 346 are provided at a lower region of the structure, which is proximal to the drain. In this way the second channel structure 346 comprises a substantially planar region 347 which can assist in the air flowing around the side wall of the second channel structure 346 rather than downward towards the plenum. Such an air flow direction can be advantageous as it reduces the likelihood of air passing through the plenum and re-entraining water that is dropped by a downstream channel structure.

It will be appreciated that the second channel structure 346 may have more than one substantially planar regions located anywhere along its length. Alternatively or additionally, regions of the second channel structure 346 may define one or more shallow regions at which points the side walls of the channel structure are present but are lower than other portions of the side walls. In this way the depth of the channel is reduced when compared with other regions of the second channel structure 346.

Figure 3a also illustrates third and fourth channel structures 348, 350 which have side walls 349, 351 that are obliquely angled relative to the base of the channel structure. The third channel structure 348 has side walls 349 that are inwardly angled towards each other, and may be referred to an open channel. The fourth channel structure 350 has side walls 351 that are outwardly angled away from each other, and may be referred to as a closed channel.

Figure 3b illustrates fifth and sixth channel structures 352, 354 which are examples of closed channel structures. The fifth channel structure 352 has a cross-section that defines an arc with a central angle greater than 180°. In this way the end edges of the arc face each other and define a closed channel. In other examples an open channel can be provided by a channel structure that has a cross-section that defines an arc with a central angle less than 180°. The arcs may or may not have a constant radius.

The sixth channel structure 354 in figure 3b has side walls that extend perpendicularly from a base. The side walls have inwardly extending lips at their distal ends so as to provide a closed channel. It will be appreciated that one or more of the geometries illustrated in figures 3a and 3b could be combined into a single channel structure or combined in any arrangement in a plurality of channel structures within a single water separator. For example, the cross- sectional shape of any of the channel structures could vary along its length as described with reference to the second channel structure 346.

In some examples, the open channel face of channels structures disclosed herein may have regions that are hydrophobic and/or hydrophilic, incorporated through either material selection or surface coating. In one example, regions of the channel structure that are proximal to the drain may be hydrophobic and regions of the channel structure that are distal to the drain may be hydrophilic. For channel structures that have a depth that varies along the length of the channel structure, surfaces of varying wettability may be provided in regions of the channel structure. Additional regions of hydrophilic and hydrophobic surfaces could be used on the walls of the plenums or baffle plates. Figure 4 illustrates a plan view of an array of channel structures 416. The array extends in a lateral direction 460 and a longitudinal direction 462 relative to the fluid flow path. The longitudinal direction 462 corresponds with the direction of fluid flow through the array of channel structures 416 as shown in figure 4. A lateral flow space is defined as a lateral spacing between adjacent channel structures 416 in the array. A longitudinal flow space is defined as a longitudinal spacing between adjacent channel structures 416, or lateral rows of channel structures in the array. One or more of the following parameters of the array can be set in order to improve water separation for any particular application:

• the width of the lateral flow spaces between channel structures 416, which may be related to the pitch between channel structures 416, may vary as a function of distance from the inlet;

• the longitudinal depth of the channel structures 416, which may vary as a function of distance from the inlet;

• the lateral width of the channel structures 416, which may vary as a function of distance from the inlet;

• the number of channel structures in a lateral row of channel structures, which may vary as a function of distance from the inlet; and

• the longitudinal spacing between adjacent rows of channel structures, which may vary as a function of distance from the inlet.

Any of the above variations may be a monotonically increasing or decreasing function, or may be a more complex function.

It will be appreciated that one or more of the geometries and features of the channel structures described with reference to figures 3a and 3b could be used with one or more of the array parameters described with reference to figure 4.

Any of the water separators disclosed herein can be located in the exhaust pipe work of the fuel cell, either before or after a heat exchanger.

Figure 5 illustrates a water separator 506 that is similar to the one illustrated in figure 1c. Features in common between the two water separators will not necessarily be described again here.

The water separator 506 of figure 5 includes a cooling means that cools the plurality of channel structures 516. Such a cooling means can increase the amount of water that condenses out of the exhaust fluid at the channel structures, thereby further improving the degree of water separation.

In this example, the cooling means is provided by passing coolant through a conduit that passes through each of the channel structures 516. Figure 6 illustrates a channel structure 616 that has a coolant conduit 678 passing through it. Such a channel structure 616 may be used in the water separator of figure 5.

As shown in figure 5, the upper end of the coolant conduit of each channel structure 516 opens into a coolant inlet manifold 572, which receives coolant from a coolant inlet 570. Similarly, the lower end of the coolant conduit of each channel structure 516 opens into a coolant outlet manifold 576, which provides coolant to a coolant outlet 574. The coolant inlet 570 and coolant outlet 574 can be part of a coolant circuit/loop that is used to remove heat from the channel structures 516.

The material selection or coating of the channel structures can be modified accordingly to optimise the rate of heat transfer between the hot two-phase mixture and the cold coolant channel. For any specific application, the coolant outlet manifold 576 can be designed such that it does not significantly impede air flow though the water separator 506 or water drainage from the water separator 506. Alternatively, the coolant outlet manifold may be designed such that it replaces the baffle plates shown in figure 1 with reference 120 and provides additional cooling in the plenum region. Alternatively, it may feed directly into a heat sink.

In addition to increasing the amount of condensation at the channel structures 516, use of such a cooling means also reduces the temperature of the exhaust fluid that exits the water separator 506. This can be particularly beneficial for fuel cell systems that require the exhaust fluid to be cooled before it is vented to the environment; such systems conventionally use a heat exchanger to cool the exhaust fluid. The water separator 506 of figure 5 may be provided instead of a conventional heat exchanger in a fuel cell system. In this way, the complexity, volume occupied and cost of the system can be greatly reduced as a single component can provide both water separation and exhaust heat reduction. Even if an additional heat exchanger is required, the thermal duty and physical size of such a heat exchanger can advantageously be significantly reduced.

The exhaust fluid that flows through the separation chamber can be considered as the hot fluid that flows through the heat exchanger and the coolant can be considered as the cold fluid that flows through the heat exchanger. It will be appreciated that a single fluid processing component can be provided that provides the functionality of both a liquid separator and a heat exchanger, and that such a fluid processing component can be provided independently of any fuel cell system described in this document.

One or more of the liquid separators disclosed herein may be particularly advantageous for coupling to the cathode exhaust of an evaporatively cooled fuel cell, as such fuel cell systems may benefit from being able to recover water from the cathode exhaust fluid so that the recovered water can be re-used. The liquid separators disclosed in this document may also be useful for separating liquid out of an exhaust from a liquid cooled fuel cell.

Throughout the present specification, the descriptors relating to relative orientation and position, such as "top", "bottom" and "side" as well as any adjective and adverb derivatives thereof, are used in the sense of the orientation of the fuel cell system as presented in the drawings. However, such descriptors are not intended to be in any way limiting to an intended use of the described or claimed invention.

Claims

1. A fuel cell system comprising:

a fuel cell having an exhaust; and

a liquid separator comprising:

an inlet coupled to the exhaust of the fuel cell;

an outlet;

a drain; and

2. The fuel cell system of claim 1 , further comprising a cooling means configured to cool the plurality of channel structures.

3. The fuel cell system of claim 2, wherein the cooling means comprises a conduit passing through each of the plurality of channel structures, the conduit configured to receive a coolant.

4. The fuel cell system of any preceding claim, wherein the channel axis extends towards the drain in a downward direction.

5. The fuel cell system of any preceding claim, wherein the channel axis extends in a direction that is transverse to the fluid flow path.

6. The fuel cell system of any preceding claim, wherein the channel structures each comprise a C-shaped channel having two side walls and a base.

7. The fuel cell system of claim 6, wherein the side walls of the C-shaped channel are obliquely angled to the base of the C-shaped channel.

8. The fuel cell system of claim 6 or claim 7, wherein the depth of the C-shaped channel varies along the length of the channel.

9. The fuel cell system of any one of claims 6 to 8, wherein the channel structures comprises a substantially planar region.

10. The fuel cell system of any preceding claim, in which the plurality of channel structures are disposed in a laterally and longitudinally extending array relative to the flow path, and the plurality of channel structures are each separated from one another by a lateral flow space and a longitudinal flow space.

11. The fuel cell system of claim 10, wherein the lateral width of flow spaces between channel structures varies as a function of distance from the inlet.

12. The fuel cell system of claim 10 or claim 11 , wherein the lateral width of the channel structures varies as a function of distance from the inlet.

13. The fuel cell system of any one of claims 10 to 12, wherein the longitudinal depth of the channel structures varies as a function of distance from the inlet.

14. The fuel cell system of any one of claims 10 to 13, wherein the number of channel structures in a lateral row of channel structures varies as a function of distance from the inlet

15. The fuel cell system of any preceding claim, wherein the open channel faces of the channel structures comprise a hydrophobic region proximal to the drain and a hydrophilic region distal to the drain.

16. The fuel cell system of any preceding claim, further comprising a plenum between the bottom of the channel structures and a bottom surface of the separation chamber.

17. The fuel cell system of claim 16, further comprising a first baffle plate located in the plenum, wherein the first baffle plate is in a plane transverse to the channel axis of the channel structure, wherein the first baffle plate extends over the majority, but not all, of the footprint of the separation chamber.

18. The fuel cell system of claim 17, further comprising a second baffle plate provided in the flow path between the first baffle plate and the outlet, wherein the second baffle plate extends from the wall in which the outlet is provided at a position that is between the first baffle plate and the outlet.

19. The fuel cell system of any preceding claim, wherein the exhaust of the fuel cell is a cathode exhaust.

20. A fluid processing component comprising:

a liquid separator comprising:

an inlet;

an outlet;

a drain; and

a cooling means configured to cool the plurality of channel structures.

21. A fuel cell system substantially as described herein with reference to the accompanying figures.

22. A fluid processing component substantially as described herein with reference to the accompanying figures.