Separation system for a fuel cell system

Abstract

A separation system, in particular for fuel cell systems, is known, comprising an upwardly open first container (10) for separating a liquid from a two-phase mixture (17), the first container having a feed (16) through which the two-phase mixture (17) can be fed, an upper first outlet (22) through which gas can be drawn, and a lower second outlet through which liquid can be drawn, and a second upwardly open container (12) having an outlet (32). In order to continuously obtain accurate measurement results related to the amount of condensate generated, according to the present invention, the outlet opening (30) of the outlet part (32) of the open second container (12) is geodetically arranged above the bottom (34) of the first container (10) and above the bottom (36) of the second container (12), the second outlet (26) of the first container (10) is fluidly connected to the inlet (28) to the second container (12) via the measuring pipe (14), and the separation system has a flow meter (40) that functions geodetically below the outlet opening (30) for measuring the flow rate in the measuring pipe (14) between the first container (10) and the second container (12).

Description

[Technical field]

[0001] The present invention relates to a separation system for a fuel cell system, comprising a first container open towards the top for separating a liquid from a two-phase mixture, the first container having a supply part through which the two-phase mixture can be supplied, an upper first outlet through which gas can be drawn off, and a lower second outlet through which liquid can be drawn off, and a second container open towards the top and having an outlet part. [Background technology]

[0002] Fuel cell systems are used both in domestic heating and in mobile applications, for example for generating electrical current to drive electric motors in electrically driven automobiles.

[0003] However, the water content is an important parameter during the operation of PEM fuel cells. The water or water vapor generated during the reaction at the cathode must be discharged to prevent it from condensing and wetting the catalyst surface, which would otherwise reduce the power density of the fuel cell. Furthermore, liquid water impedes gas transport in the diffusion layer, while the ionic conductivity of the membrane increases with the water content. The water generated is first generated on the cathode side during the reaction, but also partially reaches the anode side, because the water vapor or water generated on the cathode side partially diffuses through the membrane or passes through it due to the dipole properties of the water molecules.

[0004] Therefore, for stable cell operation in the region of maximum power density, it is necessary to optimize the water content of the cell, and to this end, the amount of condensed water that occurs at both the cathode and the anode must be specified.

[0005] For this reason, there is a need to provide a separation system for a fuel cell system, in particular a PEM fuel cell system, which separates a two-phase mixture having water and water vapor contained in the cathode circuit, the anode circuit and / or the exhaust gas stream into gas and condensed water, and which determines the amount of condensed water generated per unit of time.

[0006] A gas separator from which the produced water or the produced liquid is discharged is known from DE 10 2016 116 989 A1. The measuring tube gas separator is supplied with a multiphase medium which flows in the measuring tube over a weir. This forms a shallow water area over which the gas is separated from the liquid. The measuring tube is provided with an upper opening for discharging the gas, while the liquid continues to flow downstream of the weir along an inclined surface to a liquid outlet where a flow meter is arranged for determining the liquid flow rate.

[0007] However, this gas separator is not suitable for fuel cell systems, since condensation is not continuous and therefore there is no continuous flow in the flow meter, which is either partially liquid-free or must be emptied discontinuously. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem is therefore to provide a separation system which can continuously and accurately measure the amount of condensate produced, while requiring as little construction space as possible. [Means for solving the problem]

[0009] This problem is solved by a separation system, in particular for a fuel cell system, which has the features of claim 1.

[0010] The separation system has two containers open toward the top, connected to each other via measuring tubes, so that the separation system is a communicating container in which the liquid level is always the same. This ensures that the liquid level is always on an equipotential line in both containers, at least as fast as the withdrawal of a liquid volume from the first or second container is possible as the supply of a liquid volume into the corresponding container. The terms above, below, upper and lower are therefore defined in correspondence with the gravitational potential or in relation to the center of the Earth. Equal height therefore means an arrangement on an equipotential line of gravity. A geodesically upper outlet therefore means an outlet that is further away from the center of the Earth than a lower outlet. When defined as above the bottom, this therefore means that the distance to the center of gravity of the Earth is greater than the distance of the bottom relative to the Earth, in other words that the gravitational potential is less than at the bottom. Correspondingly, the multiphase mixture flows via the supply into the first container open toward the top. In this container, the separation of the liquid from the multiphase mixture takes place. The gas is discharged through the geodetically upper first outlet, while the liquid flows through the lower second outlet into the measuring tube and from the measuring tube into the upwardly opening second container. An outlet is provided in the second container, the outlet opening of which is arranged geodetically above the bottom of the first container and the bottom of the second container. The second outlet of the first container is thus fluidly connected to the inlet to the second container via the measuring tube. In the measuring tube or in the measuring tube, according to the invention, a measuring device or a necessary sensor of the measuring device is arranged geodetically below the outlet opening, which measures the flow rate in the measuring tube between the first and second containers. It is not essential that the entire measuring device has a direct mechanical connection with the measuring tube and is arranged below the outlet opening, the liquid flow in the measuring tube itself is measured by the measuring device below the outlet opening. The measuring device therefore serves for flow measurement in the measuring tube below the outlet opening, so that the measurement takes place geodesically below the outlet opening, so that the flow measuring device always measures in the area circulated by the liquid, whereby even small flows can be measured, since the entire cross section is circulated.The separation system must be filled correspondingly only once up to the outlet opening. Once this has been done, all subsequent flow events are recorded by the measuring device, because the flow always takes place completely from the first container to the second container and from the second container to the outlet. Thus, in a small space, very accurate measurements are possible even for small amounts of condensate, and this measurement can be carried out continuously.

[0011] Preferably, the measuring device is an ultrasonic sensor, which can measure the flow of transparent materials regardless of the ambient conditions present, and furthermore, the measurement is performed contact-free, so that the flow is not affected.

[0012] Advantageously, the feed to the first vessel is located geodesically above the outlet opening of the outlet in the second vessel. Correspondingly, the multiphase mixture has to flow along the free area not filled with liquid, in which both phases are well separated from each other on the basis of sliding along the surface.

[0013] In order to additionally improve this separation, a slope is formed in the first vessel below the feed, geodesically above the outlet opening of the second vessel, which slopes downward in the direction from the feed towards the second outlet, correspondingly lengthening the section along which the multiphase mixture is guided above the liquid column and thus increasing the separation efficiency.

[0014] Preferably, the measuring tube is designed to rise from the first container into the second container, whereby additional degassing is achieved.

[0015] It is furthermore advantageous if a net, screen or mesh is disposed at the first outlet of the first vessel, which serves to prevent larger droplets in the gas from exiting the separation system via the first outlet.

[0016] Particularly less construction space is required if the first container is arranged concentrically with respect to the second container, so that both containers are arranged radially inside and outside one another accordingly, which also reduces material costs, since the outer wall of the inner container simultaneously forms the inner wall of the outer container, thereby requiring less material.

[0017] In a further development of this arrangement, the second container is arranged radially inside the first container, so that the supply is still easily accessible and connectable. Furthermore, the inclined surface can be formed as a simple spiral between the two outer circumferential surfaces of the container, which ensures good separation efficiency.

[0018] The downstream end of the measuring tube therefore runs through the first vessel to the inlet of the second vessel, thus ensuring a short connection with only a small inertial delay during measurement.

[0019] It is also advantageous if the geodesically lower region of the outlet opening is designed discontinuously. If the outlet opening is designed on an equipotential line, surface tension forces would result in slightly different filling levels, which would distort the measured values. This can be prevented with a discontinuous design, since the same surface tension forces would not be created over the entire circumference.

[0020] This discontinuous configuration can be produced particularly easily by arranging the edges of the outflow openings on an equipotential line that is interrupted by at least one notch.

[0021] In another embodiment, a first level sensor is arranged in the first container, which allows the error due to the delay in the formation and disappearance of the pressure difference existing between the two containers, which causes the flow in the measuring tube, to be calculated during the continuous flow measurement. For this purpose, for example, the storage volume in the first container, calculated based on the height difference, can be added to the measured value of the flowmeter.

[0022] In addition, a level sensor can additionally be placed in the second container to ensure that the volume in the second container matches the level up to the outflow opening, so that the actual volume difference is always added.

[0023] In order to prevent the first container from overflowing into the surroundings and thus from being damaged, an overflow is provided between the first container and the second container, which overflow is arranged geodetically above the outlet opening of the second container, so that, in the event of a condensate quantity occurring which is no longer able to be discharged via the measuring tube, this quantity is reliably discharged via the outlet of the second container.

[0024] A further improvement of the measured values ​​can be achieved by arranging a heat exchanger for conditioning upstream of the second vessel. This heat exchanger, which can be configured as a cooler, in particular as a simple cooler, serves to achieve additional condensation in the two-phase mixture, so that a larger proportion of water can be separated in liquid form. This allows a more accurate indication of the amount of water present in the system.

[0025] Thus, a separation system for multiphase mixtures is provided which, on the one hand, achieves high separation rates and, on the other hand, allows for continuous measurement of an accurate condensate amount or condensate flow rate. When used in a fuel cell system, this separation system facilitates an indication of the moisture situation and thus of the achievable power density of the fuel cell system.

[0026] One embodiment of a separation system according to the invention, which is suitable both for fuel cell systems and for other multiphase mixtures, such as, for example, natural gas / water mixtures, is shown diagrammatically in the drawing and is described below. [Brief description of the drawings]

[0027] [Figure 1] 1 is a principle diagram of a separation system according to the present invention, seen from the side; [Diagram 2] 1 shows a side view in cross section of an embodiment of a separation system according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The separation system according to the present invention shown in FIG. 1 comprises a first container 10 which is open towards the top and a second container 12 which is also open towards the top, the containers 10, 12 being connected to each other via a measuring tube 14.

[0029] The first container 10 has a supply 16 through which a two-phase mixture 17 flows into the container 10, consisting of air, oxygen, hydrogen and water present in liquid phase, for example if the separation system is used for a fuel cell system. The water in this case is condensed water 18 which is generated during the chemical reaction in the fuel cell and which is at least partially discharged from the fuel cell. This two-phase mixture flows over the surface along a plate formed as an inclined surface 20, where the two phases can separate from each other. The gas can escape upwards through an upper first outlet 22, which is fitted with a fine mesh grid, screen or net 24, ensuring that liquid droplets are not entrained by the gas into the first outlet 22, because they fall off the net 24 and flow back into the first container 10.

[0030] The liquid, or condensate 18, collects in the first vessel 10, flows into the measuring tube 14 via the second outlet 26, which is arranged in the lower area of ​​the first vessel 10, and into the second vessel 12 via the inlet 28 of the second vessel 12, until a level compensation between the two vessels 10, 12 is established. This level compensation therefore works via the principle of communicating vessels, which are always filled to one common equipotential plane, i.e. the filling height is determined in this case by the outflow opening 30 of the outlet 32 ​​from the second vessel 12, and it is necessary for the level compensation that the first bottom 34 of the first vessel 10 and the second bottom 36 of the second vessel 12 are arranged geodesically below the outflow opening 30.

[0031] The liquid now always seeks to establish a compensation for the filling height between the two containers 10, 12, while this filling height is always the same, i.e. corresponds to a plane subtended through the edge 38 of the outlet opening 30, provided that the volumetric flow of condensate into the first container 10 is not greater than the maximum volumetric flow that can flow through the measuring tube 14. Otherwise, the volumetric flow in the measuring tube 14 corresponds to the condensate volumetric flow into the first container 10. The volumetric flow in the measuring tube 14 is therefore measured by a flowmeter 40, which in this example is configured as an ultrasonic device with two sensors 42, 44 attached to the measuring tube 14.

[0032] A first level sensor 46 is arranged in the first container 10 and a second level sensor 48 is arranged in the second container 12 in order to take into account very rapid and continuous measurements, which may take into account time intervals during which no level compensation between the two containers has yet taken place. The measured values ​​of the two level sensors 46, 48 can be used in addition to the measured value of the flowmeter 40, since the difference between the measured values ​​of the two level sensors 46, 48 corresponds to the volume flow which additionally flows into the container in the corresponding second unit. Time delays due to decreases and increases in the height difference can thus be compensated for by adding the volume calculated on this basis to the integral value of the flowmeter 40, so that the total volume flowed in during the time interval is calculated.

[0033] 1 further illustrates the preconditioning of the two-phase mixture 17 by a heat exchanger 50, which is located upstream of the feed 16, but which may also be located within the vessel 10 or at the second outlet 26 of the vessel 10. This heat exchanger 50 serves to separate additional water, still present as water vapor, from the two-phase mixture in order to allow a more accurate water balance in the fuel cell.

[0034] Furthermore, the separation system has an overflow 52, ​​through which the condensate 18 can flow from the first container 10 into the second container 12 and from the second container 12 to the outlet 32 ​​in the event of an excessively high volumetric flow rate, thus preventing the first container 10 from overflowing.

[0035] In Fig. 2 such a separation system is illustrated with respect to a possible structural design. Both open vessels 10, 12 are arranged concentrically relative to each other, so that the first vessel 10 radially surrounds the second vessel 12, while both vessels 10, 12 have one common bottom 34, 36 and the inner circumferential surface 54 of the first vessel 10 coincides with the outer circumferential surface 56 of the second vessel 12. Between the inner circumferential surface 54 and the outer circumferential surface 58 of the first vessel 10, a spirally extending inclined surface 60 is formed, which is located geodesically above the outlet opening 30 of the second vessel 12, so that on this inclined surface 60, when the two-phase mixture 17 is fed, always only a thin film is guided along this inclined surface 60, which leads to a good separation of the gas from the condensate 18.

[0036] The measuring tube 14 runs outward from the second outlet 26 in the lower region of the first container 10, where the measurement by the flowmeter 40 is carried out, through the outer circumferential surface 58 of the first container 10 and through the first container 10 to the inner circumferential surface 54 of the first container 10 or the outer circumferential surface 56 of the second container 12. The outer circumferential surface 56 of the second container is provided with an opening serving as the inlet 28, so that the downstream end 62 of the measuring tube 14 runs through the first container 10. The measuring tube 14 is designed to rise from the first container 10 to the second container 12, which prevents the accumulation of gas that has not yet left the measuring tube 14.

[0037] Additionally, in FIG. 2 it can be seen that a notch 64 is formed in the edge 38 of the outflow opening 30, however this notch is not large enough to act as an outflow opening, it simply disturbs the surface tension in the plane of the outflow opening 30, thereby preventing a higher level in the second container 12 based on surface tension.

[0038] The separation system allows the amount of condensate occurring in a fuel cell system to be determined very precisely and continuously on both the cathode and anode side. Such a system is also available on the exhaust gas side. The separation system is distinguished by its small design, high separation rate and precise measurement values. As a result, the power density of the fuel cell can be increased.

[0039] It will be clear that the scope of protection of claim 1 is not limited to the described embodiment. In particular, such a separation system can be used not only in fuel cell systems but also in other fields where a two-phase mixture has to be separated into a liquid and a gaseous portion, for example in the field of natural gas transportation or combustion, where water is present as a liquid. The flowmeter can also be configured, for example, as a measuring turbine or a Coriolis mass flowmeter. Furthermore, various constructional types of the interconnected vessels or tubes are conceivable.

Claims

1. A separation system for a fuel cell system for separating a liquid from a two-phase mixture (17), comprising a first container (10) open toward the top, the first container (10) having a feed (16) through which the two-phase mixture (17) can be fed, an upper first outlet (22) through which gas can be drawn off, and a lower second outlet through which the liquid can be drawn off, and a second container (12) open toward the top and having an outlet (32), 1. A separation system for a fuel cell system, characterized in that an outlet opening (30) of the outlet (32) of the open second vessel (12) is arranged geodetically above a bottom (34) of the first vessel (10) and above a bottom (36) of the second vessel (12), the second outlet (26) of the first vessel (10) is fluidly connected to an inlet (28) into the second vessel (12) via a measuring tube (14), and the separation system comprises a flow meter (40) which functions geodetically below the outlet opening (30) for flow measurement in the measuring tube (14) between the first vessel (10) and the second vessel (12).

2. The separation system for a fuel cell system of claim 1 , wherein the flow meter (40) is an ultrasonic sensor.

3. 3. The separation system for a fuel cell system according to claim 1 or 2, wherein the supply (16) into the first vessel (10) is arranged geodetically above the outlet opening (30) in the second vessel (12).

4. 4. The separation system for a fuel cell system according to claim 3, wherein a slope (20, 60) is formed in the first container (10) on the geodesic upper side of the outlet opening (30) of the second container (12) and below the supply (16) in the direction from the supply (16) to the second outlet (26).

5. 5. The separation system for a fuel cell system according to claim 1, wherein the measuring tube (14) is configured to rise from the first container (10) towards the second container (12).

6. The separation system for a fuel cell system according to any one of the preceding claims, further comprising a net, screen or mesh (24) disposed at the first outlet (22) of the first vessel (10).

7. The separation system for a fuel cell system according to any one of the preceding claims, wherein the first vessel (10) is arranged concentrically with respect to the second vessel (12).

8. The separation system for a fuel cell system according to claim 7, wherein said second vessel (12) is disposed radially inward of said first vessel (10).

9. 9. The separation system for a fuel cell system according to claim 8, wherein the measuring tube (14) extends at an upstream end (62) through the first vessel (10) to the inlet (28) of the second vessel (12).

10. 10. The separation system for a fuel cell system according to claim 1, wherein the geodesically lower area of ​​the outlet opening (30) is not configured continuously.

11. 11. The separation system for a fuel cell system according to claim 1, wherein the edges (38) of the outlet openings (30) are arranged on an equipotential line, the gradual edges (38) being interrupted by at least one notch (64).

12. The separation system for a fuel cell system according to any one of the preceding claims, further comprising a first level sensor (46) disposed in the first vessel (10).

13. The isolation system for a fuel cell system of claim 12, further comprising a second level sensor (48) disposed within the second vessel (12).

14. 14. The separation system for a fuel cell system according to claim 1, wherein an overflow (52) is provided between the first container (10) and the second container (12), the overflow (52) being located geodesically above the outlet opening (30) of the second container (12).

15. 15. The separation system for a fuel cell system according to any one of the preceding claims, further comprising a heat exchanger (50) arranged upstream of the second vessel (12).

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