WO2015150795A1

WO2015150795A1 - A fuel cell system with fuel gas pressure regulator

Info

Publication number: WO2015150795A1
Application number: PCT/GB2015/051001
Authority: WO
Inventors: Sophie Charlotte HARRIS
Original assignee: Intelligent Energy Limited
Priority date: 2014-04-03
Filing date: 2015-03-31
Publication date: 2015-10-08
Also published as: GB2524803A; GB201406019D0

Abstract

A fuel cell system (100) comprising a fuel cell (102) having an anode inlet port (104) and a cathode fluid communication port (108) and an anode pressure regulator (112). The anode pressure regulator (112) comprising a cathode chamber (114) with a cathode chamber inlet port (116); an anode chamber (118) with an anode chamber outlet port (120) and an anode chamber inlet port (122); a diaphragm (124) between the cathode chamber (114) and the anode chamber (118); and a variable restriction element (126) configured to control the flow of fluid into the anode chamber (118) through the anode chamber inlet port (122) in accordance with the position of the diaphragm (124). The cathode chamber inlet port (116) is in fluid communication with the cathode fluid communication port (108) of the fuel cell (102). The anode chamber outlet port (120) is in fluid communication with the anode inlet port (104) of the fuel cell (102). The anode chamber inlet port (122) is configured to be in fluid communication with a fuel source for the fuel cell.

Description

A FUEL CELL SYSTEM WITH FUEL GAS PRESSURE REGULATOR

This disclosure relates to a fuel cell system, in particular, a fuel cell system that includes an anode pressure regulator.

Electronically controlled valves can be used to control fluid flow in fuel cell systems in order to regulate fluid pressures.

In accordance with a first aspect of the invention there is provided a fuel cell system comprising:

a fuel cell having an anode inlet port and a cathode fluid communication port; and an anode pressure regulator comprising:

a cathode chamber with a cathode chamber inlet port;

an anode chamber with an anode chamber outlet port and an anode chamber inlet port;

a diaphragm between the cathode chamber and the anode chamber; and a variable restriction element configured to control the flow of fluid into the anode chamber through the anode chamber inlet port in accordance with the position of the diaphragm;

wherein:

the cathode chamber inlet port is in fluid communication with the cathode fluid communication port of the fuel cell;

the anode chamber outlet port is in fluid communication with the anode inlet port of the fuel cell; and

the anode chamber inlet port is configured to be in fluid communication with a fuel source for the fuel cell.

Such a fuel cell system can provide an effective mechanism for modulating the pressure of fluids on an anode side of the fuel cell with reference to the pressure of fluids on a cathode side of the fuel cell, which may not require any electronic control. In this way, the pressure differential across a membrane in the fuel cell can be controlled such that the likelihood of damage to the fuel cell can be reduced.

The variable restriction element may be configured to control the flow of fuel into the anode chamber through the anode chamber inlet port in accordance with the position of the diaphragm. The variable restriction element may be configured to control the flow of fluid into the anode chamber through the anode chamber inlet port such that the diaphragm tends towards a predetermined position. The predetermined position may be a planar orientation. The variable restriction element may be configured to control the flow of fluid into the anode chamber through the anode chamber inlet port such that a pressure of fluid in the anode chamber tends towards a pressure of fluid in the cathode chamber.

The fuel cell system may further comprise a biasing element configured to apply a bias force to the diaphragm. The biasing element may comprise a spring configured to apply a bias force to the diaphragm either towards or away from the anode chamber. The biasing element may be an adjustable biasing element.

The variable restriction element may comprise a valve. The valve may comprise a variable orifice valve, a globe valve, or a poppet valve.

The fuel cell system may further comprise a mechanical linking element configured to provide a mechanical link between the position of the diaphragm and a degree of restriction to flow provided by the variable restriction element. The mechanical linking element may be configured to mechanically translate a component of the variable restriction element when the diaphragm moves towards or away from the anode chamber.

The cathode fluid communication port may be a cathode inlet port or a cathode outlet port. The diaphragm may provide a fluid isolation between the cathode chamber and the anode chamber. The diaphragm may comprise a dual diaphragm.

Embodiments of the present invention will be described with reference to the accompanying drawing, in which:

figure 1 shows a fuel cell system.

One or more examples disclosed in this document relate to an anode pressure regulator that can track / modulate the pressure of fluids on an anode side of fuel cells in a fuel cell stack with reference to the pressure of fluids on a cathode side of the fuel cells. In this way, the pressure differential across the fuel cells can advantageously be controlled, which can reduce the likelihood of damage to the fuel cells or the fuel cell stack, thereby making an associated fuel cell system more reliable. Figure 1 shows a fuel cell system 100 comprising one or more fuel cells. In this example a plurality of fuel cells are provided as a fuel cell stack 102. The fuel cell stack 102 has an anode inlet port 104 and an anode outlet port 106. The anode inlet port 104 and the anode outlet port 106 are examples of anode fluid communication ports. The fuel cell stack 102 also has a cathode inlet port 108 and a cathode outlet port 1 10. The cathode inlet port 108 and the cathode outlet port 110 are examples of cathode fluid communication ports.

The fuel cell system 100 also includes an anode pressure regulator 112. The anode pressure regulator 1 12 comprises a cathode chamber 114 and an anode chamber 118.

The cathode chamber 114 has a cathode chamber inlet port 116. The anode chamber

118 has an anode chamber outlet port 120 and an anode chamber inlet port 122. A diaphragm 124 is located between the cathode chamber 114 and the anode chamber 118.

A first surface of the diaphragm 124 provides an interior surface of a wall that defines the cathode chamber 114. A second surface of the diaphragm 124 provides an interior surface of a wall that defines the anode chamber 1 18, where the first surface of the diaphragm 114 opposes the second surface.

As is well-known, the diaphragm 124 can be provided as a sheet of semi-flexible material anchored at its periphery to provide a barrier to fluid flow between the cathode chamber 114 and the anode chamber 118. The diaphragm 124 can move into one of the chambers 114, 118 depending on a difference in pressure of fluids within the two chambers 114, 118. In this way, the diaphragm 124 can provide fluid isolation between the cathode chamber 114 and the anode chamber 1 8 and can deform in accordance with any difference in pressure between the fluid in the anode chamber 118 and the fluid in the cathode chamber 114.

The anode pressure regulator 112 also includes a variable restriction element, which in this example is a valve 126. The valve 126 controls the flow of fluid (which in this example is fuel) into the anode chamber 118 through the anode chamber inlet port 122 in accordance with the position / orientation of the diaphragm 124, for example in accordance with a degree of deformation of the diaphragm 124. In this example a mechanical linking element 128 provides a mechanical link between the position of the diaphragm 124 and a degree of restriction to flow provided by the valve 126. The mechanical linking element 124 may be a rod or a pin that can mechanically translate a component of the valve 126 when the diaphragm 124 moves towards or away from the anode chamber 118. The specific component that is mechanically translated within the valve 126 will depend upon the type of valve that is used. The valve 126 can be one of a variable orifice valve, a globe valve and a poppet valve, as non-limiting examples.

The cathode chamber inlet port 116 is in fluid communication with the cathode inlet port 108 of the fuel cell stack 102, in this example via a "cathode to anode link pipe" 134. A compressor 130 can be used to control the air flow through the cathode sides of the fuel cells in the fuel cell stack 102, thereby controlling the power output of the fuel cell stack 102. The output of the compressor 130 is therefore in fluid communication with both the cathode chamber inlet port 116 and the cathode inlet port 108 of the fuel cell stack 102. In this way, the pressure of fluid within the cathode chamber 114 of the anode pressure regulator 112 is linked to the pressure of fluid on the cathode sides of the fuel cells in the fuel cell stack 102.

In alternative embodiments, the cathode chamber inlet port 116 can be in fluid communication with the cathode outlet port 110 of the fuel cell stack 102. In some applications this can be less advantageous than connecting the cathode chamber inlet port 116 to the cathode inlet port 108 because there may be a pressure drop in the cathode fluid across the fuel cell stack. However, as will be discussed in more detail below, a biasing element such as a spring 132 may be provided to apply a bias force to the diaphragm 124 to account for any such pressure drop.

The anode chamber 1 18 may be configured to be in fluid communication with, and between, the anode inlet port 104 of the fuel cell stack 102 and the fuel source. The anode chamber outlet port 120 may be in fluid communication with, and between, the anode inlet port 122 of the fuel cell stack 102 and the anode chamber inlet port 122. The anode chamber outlet port 120 is in fluid communication with the anode inlet port 104 of the fuel cell stack 102. The anode chamber inlet port 122 is configured to be in fluid communication with a fuel source (not shown) for the fuel cell stack 102. In this example, the fuel source is a source of hydrogen gas.

The valve 126 can control the flow of fluid into the anode chamber 118 through the anode chamber inlet port 122 such that the diaphragm 124 tends towards a predetermined or preformed orientation / position, in this example so that it is substantially planar. In this way, the pressure of the anode fluid (fuel) in the anode chamber 1 18 tends towards the pressure of the cathode fluid (air) in the cathode chamber 1 14, such that the pressures are generally equalised. Therefore, due to the connections between the anode chamber 1 18, the cathode chamber 1 14 and the fuel cell stack 102, the pressure of the anode fluids and the cathode fluids on each side of the membranes in the fuel cells are also generally equalised. Advantageously, this causes a reduction in membrane flexure and therefore can improve the reliability of the fuel cell stack. The anode pressure regulator 112 of figure 1 also includes an optional biasing element that is configured to apply a bias force to the diaphragm 124. In this example the biasing element is a spring 132 that applies a bias force to the diaphragm 124 either towards or away from the anode chamber 118 / cathode chamber 114. For example, the spring 132 may apply a predetermined bias force to the diaphragm 124 when it is planar. This can be used to apply a preset / offset to the pressure balancing between the fluid in the cathode chamber 114 and the fluid in the anode chamber 1 18. Such a preset can be useful where it is considered beneficial to operate the fuel cell stack 102 with a specific pressure differential across the membranes of the fuel cells. Also, a preset can be useful where the pressure of one or both of the fluids in the cathode chamber 1 14 and the anode chamber 118 are expected to be different to the pressure of the fluids in the fuel cell stack 102. For example, if the cathode chamber inlet port 116 is connected to the cathode outlet port 110 of the fuel cell stack 102, then the bias force applied by the spring 132 can be set such that any pressure drop in the cathode flow path through the fuel cell stack 102 can be accounted for by the anode pressure regulator 112. In this way, it can still be possible to adequately control the pressure differential across the fuel cell membranes in the fuel cell stack, for example to minimise, or keep to an acceptably low level, the pressure differential.

The spring 132 can be adjustable by a user such that it applies a required bias force to the diaphragm 124. That is, the spring 132 can be an adjustable biasing element. This can allow an engineer to set a desired bias force level when commissioning / installing the anode pressure regulator 112.

The fuel cell stack 102 may be an evaporatively cooled system, that is, one in which a coolant such as water is provided to the cathode inlet port 108 for evaporative cooling the fuel cells in the fuel cell stack 102. In such evaporatively cooled systems, the cathode pressure could otherwise vary outside tolerable levels for cross-membrane differential pressure.

The anode pressure regulator 112 described herein can provide advantages over electronic valves in some applications. This can be because the anode pressure regulator 112 may not require a reference pressure transducer at both the cathode and anode sides of the fuel cell stack 102, and additional control mechanisms including dedicated code in a controlling electronic control unit may not be needed. Also, the anode pressure regulator 1 12 can be better than pressure-over-pressure regulators in some applications because separate pilot regulators for setting a base working pressure may not be necessary. Examples disclosed herein can negate the need for electronic control and can combine the required pressure regulation functionality into a single mechanical device. They can also optionally be preset to a base pressure setting using a biasing element such as a spring and a screw. The use of a cathode connection to an atmospheric side of the control diaphragm in the regulator can result in an additional set pressure when the cathode is pressurised. As this cathode pressure changes, the additional set pressure changes. This alters the delivery pressure on the anode / hydrogen side of the regulator to match the cathode pressure.

In operation a preset pressure could be dialled into the regulator, for example using a spring and screw biasing element. This would not change during operation, and could be set such that it is slightly lower than the operating pressure required. Upon start-up of the fuel cell stack, the back pressure generated by the compressor at the cathode inlet port 108 is transferred to the cathode chamber inlet port 116, for example through a cathode to anode link pipe 134. This additional pressure can assist the spring pressure already acting on the regulator diaphragm 124 against the hydrogen pressure in the anode chamber 114 on the opposing side. The pressure in the anode chamber 114 then reaches a new equilibrium relative to the cathode back pressure. The higher the cathode pressure, the higher the corresponding hydrogen (anode) pressure will be. The area of the diaphragm 124 that is exposed in the cathode chamber 114 may be the same as, or different to, the area of the diaphragm 124 that is exposed in the anode chamber 118. Examples in which the exposed area is different can provide a means for applying an offset / preset between the pressure of the fluids in the cathode chamber 114 and the anode chamber 118.

If especially high cathode pressures are envisaged, then the diaphragm 124 may be provided as a dual diaphragm such that the anode pressure regulator can be considered as a dual diaphragm venting anode pressure regulator. Such a regulator can include two diaphragms back-to-back such that if one of the diaphragms ruptures then there is a back- up to maintain fluid isolation. Also, a vent passage can be provided between the two diaphragms such that in the event of a downward pressure change / release, the anode and cathode fluids can be kept separate. This can be advantageous if the compressor 130 fails or if there is a sudden shutdown as it could protect against fuel cell membrane damage from hydrogen over-pressure. The dual diaphragm can isolate the control air, or air from the compressor 130 via the cathode to anode link pipe 134, from any hydrogen that may require venting. In such examples, the mechanical linking element 128 may be configured to open an additional valve in the anode diaphragm centre to release the excess pressure through and out between the anode and cathode diaphragms. In this way, a relieving regulator may be used.

The fuel cell stack 102 may be an open cathode or a closed cathode system. In examples that relate to an open cathode fuel cell stack, the area of diaphragm 124 that is exposed in the cathode chamber 114 may be greater than the area of the diaphragm 124 that is exposed in the anode chamber 118. Alternatively, or additionally, the spring 132 may be used to provide a bias force towards the anode chamber 118. The spring 132 can be used to apply an additional pressure to match the required anode pressure relative to the cathode pressure. This would push the diaphragm 124 towards the anode chamber 118, opening the valve 126, until a pressure equilibrium was achieved. The diaphragm 124 would then be in the mid position, with valve 126 closed. One or both of these features can be used to account for the pressure of fluid in the cathode chamber 114 being less than the pressure of fluid in the cathode chamber 118, which may particularly be the case for open cathode systems.

The examples disclosed herein can be particularly advantageous at fuel cell stack start-up and at periods of high current demand, at which times there may be significant changes in the pressure of the fluid that is provided to the cathode inlet port of the fuel cell stack.

Claims

1. A fuel cell system comprising:

a cathode chamber with a cathode chamber inlet port;

wherein:

2. The fuel cell system of claim 1 , wherein the variable restriction element is configured to control the flow of fuel into the anode chamber through the anode chamber inlet port in accordance with the position of the diaphragm.

3. The fuel cell system of claim 1 , further comprising a mechanical linking element configured to provide a mechanical link between the position of the diaphragm and a degree of restriction to flow provided by the variable restriction element.

4. The fuel cell system of claim 3, wherein the mechanical linking element is configured to mechanically translate a component of the variable restriction element when the diaphragm moves towards or away from the anode chamber.

5. The fuel cell system of claim 1 , wherein the variable restriction element is configured to control the flow of fluid into the anode chamber through the anode chamber inlet port such that the diaphragm tends towards a predetermined position.

6. The fuel cell system of claim 5, wherein the predetermined position is a planar orientation.

7. The fuel cell system of claim 1 , wherein the variable restriction element is configured to control the flow of fluid into the anode chamber through the anode chamber inlet port such that a pressure of fluid in the anode chamber tends towards a pressure of fluid in the cathode chamber.

8. The fuel cell system of claim 1 , further comprising a biasing element configured to apply a bias force to the diaphragm.

9. The fuel cell system of claim 8, wherein the biasing element comprises a spring configured to apply a bias force to the diaphragm either towards or away from the anode chamber.

10. The fuel cell system of claim 8, wherein the biasing element is an adjustable biasing element.

11. The fuel cell system of claim 1 , wherein the variable restriction element comprises a valve.

12. The fuel cell system of claim 11 , wherein the valve comprises a variable orifice valve, a globe valve or a poppet valve.

13. The fuel cell system of claim 1 , wherein the cathode fluid communication port is a cathode inlet port.

14. The fuel cell system of claim 1 , wherein the cathode fluid communication port is a cathode outlet port.

15. The fuel cell system of claim 1 , wherein the diaphragm provides a fluid isolation between the cathode chamber and the anode chamber.

16. The fuel cell system of claim 1 , wherein the diaphragm comprises a dual diaphragm.

17. A fuel cell system substantially described herein and as illustrated in the accompanying drawing.