Fuel cell stack arrangement with separation unit and method for treating cathode intake air using the separation unit - Patents.com

Abstract

The invention relates to a fuel cell stack arrangement (1) comprising a fuel cell stack (3) comprising a plurality of fuel cells (3'). Each fuel cell (3') comprises an anode side (4) with a fuel inlet (5) and a fuel outlet (6), a cathode side (7) with an air inlet (8) and an air outlet (9), and an electrolyte (24) arranged between said anode side (4) and said cathode side (7). The fuel cell stack arrangement (1) further comprises a cathode air inlet (10) arranged upstream from the air inlet (8), a cathode air compressor (11) arranged downstream from the cathode air inlet (10), and a hydrogen gas storage tank (12) arranged upstream from the fuel inlet (5). The fuel cell stack arrangement (1) further comprises a first separation unit (13) comprising at least one disc stack separator (14) and arranged between the cathode air inlet (10) and the air inlet (8).

Description

[Technical field]

[0001] The present invention relates to a fuel cell stack arrangement with an improved system for the treatment of intake air, as well as a method for the treatment of the intake air of a fuel cell stack. [Background technology]

[0002] The effects of global warming are becoming even more evident, given the increase in natural disasters such as floods and temperature extremes. Growing awareness and concern has led to intense search for alternative energy sources, for example for vehicle and ship propulsion, power plants, or other energy applications.

[0003] One alternative that has emerged as a promising solution to the global warming problem is the use of fuel cells in the automotive and marine industries. Fuel cells are electrochemical cells that convert the chemical energy of fuel and oxidants into electricity through a pair of redox reactions. There are many types of fuel cells, but they all consist of an anode, a cathode, and an electrolyte that allows ions, often protons, to move between the two sides of the fuel cell. At the anode, a catalyst causes the fuel to undergo an oxidation reaction that produces ions and electrons. The ions move through the electrolyte from the anode to the cathode. At the same time, the electrons flow from the anode to the cathode through an external circuit, producing direct current electricity. At the cathode, another catalyst causes the ions, electrons, and oxygen to react to produce water and possibly other products. Thus, in addition to electricity, fuel cells produce water, heat, and, depending on the fuel source, very small amounts of nitrogen dioxide and other emissions. Multiple fuel cells can be arranged in series and / or parallel to form a fuel cell stack.

[0004] A common type of fuel cell is the proton exchange membrane (PEM) fuel cell, which consists of electrodes separated from each other by a semi-permeable proton-conducting polymer membrane. Proton exchange membranes, or polymer electrolyte membranes (PEMs), are semi-permeable membranes generally made from ionomers, designed to conduct protons while acting as an electronic insulator and reactant barrier to, for example, oxygen and hydrogen gases. On the anode side, hydrogen diffuses to the anode catalyst and dissociates into protons and electrons. The protons conduct through the membrane to the cathode, but because the membrane is electrically insulating, the electrons are forced to travel through an external power circuit. At the cathode catalyst, oxygen molecules react with the electrons and protons that have traveled through the external circuit to produce water.

[0005] Oxygen from compressed air is often used as an oxidant in fuel cells. During operation, the core components of a fuel cell are highly sensitive to particles, harmful gases, and water present in the intake air. Furthermore, harmful gases can cause irreversible damage to catalysts coated with precious metals such as platinum or gold. The intake air therefore needs to be purified to prevent premature deterioration of the fuel cell. Furthermore, the compressed air may need to be humidified, for example, if the fuel cell is a PEM fuel cell. To ensure trouble-free operation and long system life, therefore, particle filtration and harmful gas adsorption are equally important as effective water droplet separation and humidification.

[0006] Currently available fuel cell arrangements include complex systems for the treatment of the intake air before allowing it to enter the fuel cell. In particular, such systems may include a particulate filter layer that separates particulate matter from the intake air. A dedicated activated carbon layer of the filter element may be used to adsorb harmful gases such as sulfur dioxide (SO2), nitrogen oxides (NOx) and ammonia (NH3), thus protecting the fuel cell's valuable catalysts against contamination and degradation.

[0007] As mentioned above, a sufficiently high level of humidity is necessary for optimal operation of the fuel cell. For example, if the intake air is too dry, there will be a detrimental effect on the proton conductivity of the proton exchange membrane in the PEM fuel cell stack. Therefore, the humidifier can add water vapor produced by evaporation and / or process water in the form of a very fine mist from the cathode air exhaust to the intake air to increase the humidity. As a result of the method, water that is not evaporated can form water droplets, which are separated by the cathode water separator to protect the stack. The water produced by the fuel cell is returned to the humidifier by the exhaust duct and the humidity is transferred to the intake air. Excess water is removed by the water separator to protect the fuel cell against the effects of water.

[0008] Thus, a need exists for an improved fuel cell stack arrangement whereby the intake air can be effectively purified to remove particulates and water, and whereby the intake air can be humidified as needed. Summary of the Invention

[0009] In view of the above, the present invention provides a fuel cell stack arrangement capable of removing water droplets and particles that interfere with the fuel cell from the cathode air, humidifying and cooling said cathode air, and removing gaseous pollutants that are harmful to the catalyst. The fuel cell stack arrangement according to the present invention comprises a fuel cell stack comprising a plurality of fuel cells, each fuel cell comprising an anode side with a fuel inlet and a fuel outlet, a cathode side with an air inlet and an air outlet, and an electrolyte arranged between said anode side (4) and said cathode side. The fuel cells may be of any suitable type known in the art. In particular, the fuel cells may be PEM fuel cells. The term "plurality" shall be understood as at least two. The number of fuel cells may vary depending on the required electrical output of the fuel cell stack. The fuel cells in the fuel cell stack may be connected in series or in parallel to increase the total output current.

[0010] The fuel cell stack according to the invention further comprises a cathode air inlet arranged upstream from the air inlet. The cathode air inlet may be in the form of a pipe having a cross section of suitable shape and size. The air flow per unit of power at the cathode air inlet may be between 10 and 60 Nl / min / kW, preferably between 20 and 50 Nl / min / kW. The unit Nl / min stands for normalized liters of air per minute at +20°C (+68°F) and 1.01325 bar (14.69595 PSI).

[0011] In order to provide a sufficient amount of oxygen to the fuel cell stack, the intake air needs to be compressed. To this end, the fuel cell stack arrangement comprises a cathode air compressor arranged downstream from the cathode air intake. The compressor may be of any suitable type known in the art. Since the pressure increase results in an increase in temperature, the compressed intake air may need to be cooled before passing through the fuel cell stack arrangement. To this end, the fuel cell stack arrangement may comprise a cooling unit.

[0012] The hydrogen used in the fuel cell is supplied from a hydrogen gas storage tank located upstream from the fuel inlet. Hydrogen can be physically stored either as a gas or as a liquid. Storage of hydrogen as a gas typically requires high pressure tanks (350-700 bar tank pressure). Storage of hydrogen as a liquid requires cryogenic temperatures, as the boiling point of hydrogen at 1 atmosphere is -252.8°C.

[0013] The fuel cell stack arrangement further comprises a first separation unit comprising at least one disc stack separator, the first separation unit being disposed between the cathode air intake and the air inlet. The disc stack separator comprises a plurality of rotating disc elements with gas present between the discs. As a result, the disc stack separator comprises a plurality of narrow gaps between the discs, which allows for separation of small water droplets comprising particles and gas.

[0014] The present invention offers many advantages over previously available solutions, since the separation unit comprising at least one disc stack separator improves the purification of the cathode air due to its ability to deliver both water droplets and particles. It should be further emphasized that the inventive arrangement provides separation of water droplets as well as particles, thus making it possible to replace the particle filter and the water separation unit, e.g., liquid trap, by one single unit. Furthermore, the inventive arrangement makes it possible to purify, humidify and alkalize the cathode air, as will be explained in detail below.

[0015] The first separation unit may comprise a plurality of disc stack separators to achieve sufficient purification of the intake air. Each disc stack separator of the first separation unit may comprise a rotor including a stack of closely spaced conical separating discs projecting into the compartment of the first separating disc. The disc stack separator may comprise 20-250 discs, preferably 100-200 discs. The separator may be of a more basic type having radial vanes instead of conical discs on the rotor. Each separator may preferably be of counter-flow type, where the intake air flows radially inwards through the gaps between the discs against the pumping effect created by the rotational movement of the rotor. Alternatively, each separator may be of parallel flow type. When multiple disc stack separators are used, each of the separators may be of the same type or of different types.

[0016] In one embodiment, the separators are of the counter-flow type and each separator rotor may further comprise a fan rotating with the rotor. The fan may be located in an outlet chamber separate from and surrounding the separation unit. The fan may be arranged to enhance the flow of purified intake air from the separation unit to the air inlet of the fuel cell stack. If desired, instead of individual fans for each separator, a fan may be arranged upstream or downstream of the separation unit to feed the mixture of intake air, water and reaction products through the disc stack separator of the separation unit and deliver the purified intake air to the air inlet of the fuel cell stack. The disc stack separators are driven either by individual electric motors or by a common electric motor and belt transmission.

[0017] The fuel cell stack arrangement according to the invention further comprises a treatment unit arranged between the cathode air intake and the first separation unit. Preferably, the treatment unit is arranged immediately upstream of the first separation unit. In the treatment unit, a first liquid, such as water, may be introduced into the intake air flow for evaporative cooling and saturation of the intake air. The first liquid is preferably in the form of an aerosol. The term aerosol is understood in the context of the present invention as a suspension of liquid droplets in the intake air. The treatment unit may be arranged to treat the intake air so that it is humidified and harmful gases are removed. The treatment unit may be arranged for the removal of harmful gases that may be present in the intake air. To this end, small droplets of a second liquid, such as an alkaline solution, may be introduced to adsorb and dissolve the harmful gases. The second liquid may be in the form of an aerosol. Preferably, the size of the droplets in the treatment unit should be small enough not to settle due to gravity and large enough to be centrifuged.

[0018] Thus, air enters the treatment unit, and harmful gases that may be present in the intake air are dissolved in the second aerosol, while the intake air is humidified by the first aerosol. The water aerosol may be generated by a high-pressure nozzle or a piezoelectric crystal. The treatment unit and the first separation unit may be located upstream or downstream from the cathode air compressor. Preferably, the treatment unit and the first separation unit are located downstream from the cathode air compressor, so that water droplets generated when the compressed intake air is cooled can be removed by the first separation unit. When a treatment unit is present, the fuel cell stack arrangement according to the invention offers the advantage of even more compact and effective cathode air treatment, replacing the particle filter, the cathode air cleaner and the humidifier in one unit.

[0019] The first separation unit may include a first water outlet for delivering the water separated in the first separation unit. The first water outlet may be in fluid communication with the treatment unit such that the water delivered through the first water outlet is directed to the treatment unit. Such an embodiment provides the advantage of reduced water consumption.

[0020] The fuel cell stack arrangement according to the invention further comprises a second separation unit disposed between the fuel outlet and the fuel inlet. The second separation unit is configured to separate water droplets that may be present in the hydrogen gas before it is allowed to enter the fuel cell. The second separation unit may comprise a second water outlet for delivering the water separated by the second separation unit. Alternatively, the water separated by the second separation unit may be removed, for example by evaporation in a gas processing unit.

[0021] The provision of the first and second liquids in two separate steps has the following advantages: The first step of introducing the first liquid, e.g. water, results in saturation of the heated compressed intake air and evaporation providing further cooling. The temperature of the compressed intake air immediately downstream of the cathode air compressor may be 100°C to 150°C. Once the intake air is saturated, evaporation stops. The evaporation and saturation in the first liquid introduction step have the important consequence that the small droplets of the second liquid will retain their size. The saturation in the water introduction step effectively prevents evaporation from the droplets introduced in the spray step.

[0022] Preferably, the droplets of the second liquid should be small enough not to settle due to gravity, yet large enough to be centrifuged, so that they will be stably carried forward in the flow and separated from the flow in the centrifugation step.

[0023] The first liquid may be introduced by spraying small droplets of the first liquid into the flow, which provides rapid saturation and results in cooling.

[0024] Small droplets of the first liquid may be produced by atomization with pressurized air using a two-fluid nozzle or high pressure liquid spray using a one-fluid nozzle. A two-fluid nozzle can be advantageous for producing very small droplets to obtain the fastest possible cooling.

[0025] Small droplets of the second liquid may be produced by atomization with pressurized air using a two-fluid nozzle or by high pressure liquid spray using a one-fluid nozzle. A one-fluid nozzle may be advantageous for producing more droplets per unit time, which in turn may require a lower number of nozzles.

[0026] Atomization of liquids produces aerosols with small droplets for a large total surface area, allowing for short reaction times of the first and second liquids, with little or no slowing down required for a given flow rate. By performing atomization with pressurized air, the size of the droplets can be controlled by varying the flow rates of the air and water or alkaline aqueous solution.

[0027] The droplet size may be controlled by varying only the pressure of the pressurized air, which may be the case if the atomizing nozzle and alkaline solution flow rate are already determined.

[0028] The median size may be controlled to vary from about 1 to 200 μm, typically about 50 μm. Smaller droplets in the airflow may pass through the separation step in an undesirable manner. The term "size" is to be understood as the size of droplets of the median size. For example, a median size of dv50 means that 50% of the droplet volume are droplets with a diameter larger than dv50. A typical distribution for a dv50 of 50 μm includes droplets of 20 to 130 μm (10% of the volume are droplets smaller than 20 μm, 90% of the volume are droplets smaller than 130 μm).

[0029] Moreover, the size of the droplets of the first liquid should be kept as small as possible to allow complete evaporation of the first droplets, while the size of the droplets of the second liquid should be kept large enough to allow efficient separation of contaminated droplets of the second liquid.

[0030] Small droplets of the second liquid are added to the airflow downstream from the first liquid, so that the airflow may already be fully saturated. The spray of aerosol droplets may be co-current or counter-current to the airflow.

[0031] The purpose of the first liquid is only to saturate and cool the cathode intake air, while the purpose of the second liquid is to absorb harmful gases. When the second liquid is added, the components of the second liquid react with the absorbed gas, thus reducing the gas concentration at the surface of the droplet so that more gas can be absorbed.

[0032] The first liquid may be water and the second liquid may be an alkaline aqueous solution or any other solution intended to react with gases removed from the cathode inlet.

[0033] The treatment unit may comprise at least one spray nozzle for a first liquid and at least one atomizing spray nozzle for a second liquid downstream of said at least one spray nozzle for the first liquid.

[0034] The fuel cell stack arrangement may be equipped with a control device and actuation unit that can control the droplet size depending on the airflow on the cathode side. If the absorption is too low, the droplet size may be reduced. Furthermore, the control unit may control the rotation speed of the disks of the disk stack separator.

[0035] The present invention relates to a method for treating a cathode inlet air of a fuel cell stack, the method comprising the steps of: a) preparing an intake; b) compressing the intake air, thus obtaining compressed intake air; c) passing the intake air through a first separation unit comprising at least one disc stack separator to obtain a purified intake air and a waste water flow; comprising Steps b) and c) may be performed in any order; Further details regarding the method are provided below.

[0036] As mentioned above, the method of the present invention provides an improved treatment of cathode intake air, in which water droplets and particulate matter are removed using a single unit, i.e., the first separation unit. The intake air may be compressed before being directed to the first separation unit. Alternatively, the intake air may be treated in the first separation unit before being compressed. Regardless of the order of steps b) and c), the compressed and purified intake air is discharged downstream of the first separation unit.

[0037] When the processing unit is present in a fuel cell stack arrangement, the method of the present invention further comprises: d) treating the intake air in a treatment unit comprising a second liquid to obtain treated intake air. Further comprising: Step d) is performed before step c).

[0038] According to such an embodiment, the intake air is directed to a treatment unit, where an aerosol comprising a second liquid, e.g., an alkaline solution, dissolves harmful gaseous pollutants such as NOx, NH3, SO2, and the like, and simultaneously provides moisture to the intake air. The intake air treated in the treatment unit is then directed to a first separation unit, where contaminated water droplets and particulate matter are separated. Steps c) and d) may be performed before or after step b). That is, the intake air may be compressed before or after passing through the treatment unit and the first separation unit.

[0039] The method according to the invention comprises the steps of: e) directing the wastewater flow obtained in step c) to a treatment unit. It may further include.

[0040] Thus, the wastewater flow separated by the first separation unit may be directed to a treatment unit where it is reused to provide the first aerosol for humidification and cooling. Such an embodiment offers the advantage of reducing the amount of water consumed during the treatment of the intake air. [Brief description of the drawings]

[0041] Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0042] [Figure 1a] FIG. 1a illustrates a fuel cell stack arrangement of the present invention; [Figure 1b] FIG. 1b illustrates another embodiment of a fuel cell stack arrangement of the present invention; [Diagram 2] FIG. 2 shows a fuel cell stack; [Diagram 3] FIG. 3 illustrates the processing unit and the first separation unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The present invention will now be described hereinafter with reference to the accompanying drawings, which show exemplary embodiments of the present invention. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments of the present invention described herein; rather, these embodiments of the present invention are provided by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. In the drawings, the same or similar reference numerals indicate the same or similar components having the same or similar functions, unless otherwise specified.

[0044] Figure 1a illustrates a fuel cell stack arrangement 1 in which water droplets and particles that interfere with the fuel cell can be removed from the cathode air 2 to humidify and cool the cathode air. The fuel cell stack arrangement 1 illustrated in Figure 1a comprises a fuel cell stack 3 comprising a plurality of fuel cells (not shown), each fuel cell comprising an anode side 4 with a fuel inlet 5 and a fuel outlet 6, a cathode side 7 with an air inlet 8 and an air outlet 9, and an electrolyte disposed between the anode side and the cathode side.

[0045] A fuel cell 3' of the fuel cell stack 3 is shown in more detail in Figure 2. The fuel cell 3' comprises an anode 22, a cathode 23, and an electrolyte 24 that allows the transfer of protons between the two sides 22, 23 of the fuel cell 3'. In the anode 22, a catalyst causes a fuel, exemplified here by hydrogen gas, to undergo an oxidation reaction that produces hydrogen cations and electrons. The hydrogen cations move through the electrolyte 24 from the anode 22 to the cathode 23. At the same time, the electrons flow through an external circuit 25 from the anode 22 to the cathode 23, generating direct current electricity. In the cathode 23, another catalyst causes the hydrogen cations, electrons, and oxygen to react to produce water and possibly other products.

[0046] The fuel cell stack arrangement 1 further comprises a cathode air intake 10 arranged upstream from the air inlet 8. In order to provide a sufficient amount of oxygen to the fuel cell stack 3, the intake air needs to be compressed. To this end, the fuel cell stack arrangement 1 comprises a cathode air compressor 11 arranged downstream from the cathode air intake 10. The compressor 11 may be of any suitable type known in the art.

[0047] The hydrogen used in the fuel cell is supplied from a hydrogen gas storage tank 12 located upstream from the fuel inlet 5 .

[0048] The fuel cell stack arrangement 1 further comprises a first separation unit 13, which is shown in more detail in Figure 3. The first separation unit 13 comprises at least one disc stack separator 14, which is disposed between the cathode air intake 10 and the air inlet 8. The intake air 2 is directed to the first separation unit 13, where water droplets and particles are separated and delivered as waste water flow 15. The first separation unit is disposed downstream of the cathode air compressor 11.

[0049] The fuel cell stack arrangement 1 shown in FIG. 1b is similar to that shown in FIG. 1a, but further comprises a treatment unit 16 arranged between the cathode air intake 10 and the first separation unit 13. As can be seen in FIG. 1b, the treatment unit 16 is arranged immediately upstream of the first separation unit 13. As mentioned above, the treatment unit 16 may be arranged for the removal of harmful gases that may be present in the intake air 2. In the treatment unit 16, a first liquid 17, such as water, is introduced into the intake air flow for evaporative cooling, saturation of the intake air 2. A second liquid may be added to adsorb and dissolve harmful gases. Preferably, the size of the droplets in the treatment unit should be small enough not to settle by gravity and large enough to be centrifuged.

[0050] Thus, the air 2 enters the treatment unit 16, the intake air 2 is humidified and cooled by the first water aerosol 17, while harmful gases possibly present in the intake air 2 are dissolved in the second water aerosol 17'. The water aerosol 17, 17' may be generated by a high-pressure nozzle 18 or a piezoelectric crystal 19. The treatment unit 16 and the first separation unit 13 are arranged downstream from the cathode air compressor 11, so that the water droplets generated when the compressed intake air 2 is cooled can be removed by the first separation unit 13. The fuel cell stack arrangement 1 thus offers the advantage of a compact and effective treatment of the cathode air 2, the particle filter, the cathode air cleaner and the humidifier being replaced by one unit.

[0051] As can be seen in more detail in Figure 3, the first separation unit 13 comprises a first water outlet 15 through which the water separated in the first separation unit 13 is delivered. The first water outlet 15 is in fluid communication with a treatment unit 16, such that the water delivered through the first water outlet 15 is directed to the treatment unit 16. Such an embodiment offers the advantage of reduced water consumption.

[0052] The fuel cell stack arrangement 1 further comprises a second separation unit 20 disposed between the fuel outlet 6 and the fuel inlet 5. The second separation unit 20 is configured to separate water droplets that may be present in the hydrogen gas before it is allowed to enter the fuel cell. The second separation unit 20 comprises a second water outlet 21 for delivering the water separated by the second separation unit 20.

[0053] Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that modifications may be made without departing from the scope of the invention. It is intended that the detailed description be considered as illustrative and that the appended claims, including all equivalents, are intended to define the scope of the invention.

Claims

1. A fuel cell stack arrangement (1), comprising: a fuel cell stack (3) comprising a plurality of fuel cells (3'), each fuel cell (3') comprising an anode side (4) comprising a fuel inlet (5) and a fuel outlet (6), a cathode side (7) comprising an air inlet (8) and an air outlet (9), and an electrolyte (24) disposed between the anode side (4) and the cathode side (7); a cathode air intake (10) located upstream from the air inlet (8); a cathode air compressor (11) located downstream from the cathode air intake (10); a hydrogen gas storage tank (12) located upstream from the fuel inlet (5); Equipped with The fuel cell stack arrangement (1) further comprises a first separation unit (13) comprising at least one disc stack separator (14), disposed between the cathode air intake (10) and the air inlet (8). Fuel cell stack arrangement (1).

2. 2. The fuel cell stack arrangement (1) of claim 1, further comprising a second separation unit (20) comprising at least one disc stack separator, and arranged between the fuel outlet (6) and the fuel inlet (5).

3. 3. The fuel cell stack arrangement (1) according to claim 2, wherein the second separation unit (20) further comprises a second water outlet (21).

4. 2. The fuel cell stack arrangement (1) of claim 1, further comprising a treatment unit (16) containing a first liquid (17) and disposed between the cathode air intake (10) and the first separation unit (13).

5. 5. The fuel cell stack arrangement (1) according to claim 4, wherein the first liquid (17) is water.

6. 5. The fuel cell stack arrangement (1) according to claim 4, wherein the first separation unit (13) comprises a first water outlet (15), the first water outlet (15) being in fluid communication with the treatment unit (16).

7. 5. The fuel cell stack arrangement (1) according to claim 4, wherein said treatment unit (16) comprises droplets of said first liquid (17), said droplets having a particle size in the range of 1 μm to 200 μm.

8. 5. The fuel cell stack arrangement (1) according to claim 4, wherein the treatment unit (16) comprises a second liquid (17').

9. 2. The fuel cell stack arrangement (1) according to claim 1, wherein the air supply at the cathode air intake (10) is between 10 and 60 Nl / min / kW.

10. 2. The fuel cell stack arrangement (1) of claim 1, wherein said at least one disc stack separator comprises a stack of closely spaced conical separating discs.

11. The fuel cell stack arrangement (1) of claim 10, wherein the disc stack separator comprises 20 to 250 discs.

12. A method for treating cathode intake air (2) of a fuel cell stack (3), said method comprising: a) preparing an intake (2); b) compressing said intake air (2), thus obtaining a compressed intake air (2'); c) passing said intake air (2) through a first separation unit (13) comprising at least one disc stack separator (14) to obtain purified intake air and wastewater flows; comprising Steps b) and c) may be performed in any order; method.

13. The method comprises: d) treating said intake air (2) in a treatment unit (16) comprising a first liquid (17) to obtain treated intake air. and Step d) is performed before step c); The method of claim 12.

14. The method comprises: e) directing the wastewater flow obtained in step c) to the treatment unit.

14. The method of claim 13, further comprising:

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