METHOD FOR THE CONTINUOUS TREATMENT OF MULTI-PHASE FLUID STREAMS

Description

[0001] The invention relates to a method for the continuous treatment of multiphase fluid streams, a rotating separator for use in a corresponding method, and a fuel cell system for carrying out the corresponding method. The invention also discloses the use of corresponding rotating separators in the continuous treatment of multiphase fluid streams.

[0002] The subject matter of the invention is defined in the appended claims.

[0003] The use of fuel cells in automotive technology has been considered a promising option for reducing dependence on fossil fuels such as petroleum for several years. Fuel cells represent one of the most important alternatives to the use of batteries, such as lithium-ion batteries. Compared to battery technology, fuel cell technology offers specific advantages, particularly with regard to practical fuel handling, storage potential, and refill times, as well as the potential for using existing pipeline and storage infrastructure.

[0004] In fuel cells, oxygen reacts with a fuel, such as hydrogen, methane, or methanol, to form water and, if necessary, other reaction products under controlled reaction conditions. The reaction steps of the redox reaction occur spatially separated. The fuel cell consists of an anode and a cathode, separated from each other by an electrolyte, such as an electrolyte membrane.

[0005] The reactants are continuously fed into the fuel cell during operation, with the fuel usually being used in excess of stoichiometric amounts. This requires a sophisticated fluid flow system for the smooth operation of a fuel cell. To ensure the most efficient operation of the fuel cell and high utilization of the materials used, it is particularly necessary to at least partially recirculate the fluid streams exiting the fuel cell, in particular the fuel used in excess of stoichiometric amounts, into the fuel cell. In practice, however, this is associated with considerable problems, particularly because the fluid streams exiting the fuel cell regularly contain the reaction product of the chemical conversion, usually water, which is at least partially present in condensed form.When recirculating the escaping operating gases, it is important to avoid the water generated in the fuel cell and largely condensed from being returned to the fuel cell, where this could otherwise lead to, for example, unwanted flooding of the fuel cell stack.

[0006] For this reason, a water separator is often used in the fluid line system used for recirculation, or at least in the fluid line system used with the anode.

[0007] In the prior art, passive water separators are used for this purpose. However, according to the inventors' assessment, these systems can be associated with significant disadvantages. For example, they can lead to unwanted back pressures or pressure drops in the fluid line system. Particularly when the fuel cell is operated at low load and the fluid flow exiting the fuel cell stack is therefore comparatively weak, such systems also exhibit poor separation efficiencies with respect to the condensed water. In general, the separation performance of the passive systems known from the prior art is often considered inadequate.

[0008] Further information on the general technical background is disclosed, for example, in DE 102016124098 A1, EP 3189882 A1, GB 2 337473 A, DE 2020151050000 U1, DE 20302824, DE 102017215739 A1, DE 102017221309 A1 and DE 102019219992 A1.

[0009] The inventors of the present invention have now recognized that the problems known from the prior art can be solved by using a rotating separator, in particular if this is driven, for example, by a separate electric motor and thus not only removes condensed by-products from the fluid flow with excellent separation performance, but also actively ensures a sufficient flow in the fluid line system through its rotation, almost like a turbine.

[0010] However, according to the inventors' findings, the fundamentally advantageous use of rotating separators for the continuous treatment of multiphase fluid streams can also be associated with disadvantages that can be considered disadvantageous for certain applications, particularly when used in the fluid line system of a fuel cell. In this inherently extremely advantageous design, the inventors' own experiments have occasionally revealed surprising, unforeseen effects that led to unwanted performance losses in the fuel cell.

[0011] Without wishing to be bound by this theory, the inventors of the present invention assume that these performance losses of the fuel cell could be a consequence of the special performance of the rotating separator, which can occur particularly when the rotating separator is operated at a particularly high speed or separation efficiency. In this case, the water separation by the powerful rotating separator can function so well that the mole fraction of water in the gas phase emerging from the rotating separator also drops significantly. At the same time, the now very dry carrier gas is made available to the fuel cell by the rotating separator at sufficient pressure, even at low load, and circulates through the fuel cell.However, for the smooth operation of a fuel cell, it is often necessary for the electrolyte membrane used to separate the electrodes to be kept moist to enable sufficient ion transport. Without wishing to be bound by this theory, the inventors of the present invention believe that the inherently advantageous use of a rotating separator in a fuel cell, particularly in the fluid line system connected to the anode, increases the risk of the electrolyte membrane not having sufficient membrane moisture compared to conventional separators.

[0012] The object of the present invention was to remedy the problem described above and to provide a method for the extremely advantageous and innovative design of the use of a rotating separator in a fuel cell system, which is particularly suitable for the continuous processing of multi-phase fluid flows, in particular during the operation of fuel cells, and thereby avoids the disadvantages described above and enables efficient operation of the fuel cell.

[0013] The method to be specified for the continuous treatment of multiphase fluid flows, in particular during the operation of fuel cells, should make it possible to obtain a treated fluid flow even when using a rotating separator, with which an unwanted drying out of the electrolyte membrane can be prevented.

[0014] The inventors of the present invention have now recognized that in order to achieve the objects described above, a process for the continuous treatment of multiphase fluid flows must be designed in such a way that, with the advantageous use of the rotating separator, the molar fraction of the process material in the treated gas phase is not reduced by more than 50% compared to the original gas phase.

[0015] The above-mentioned objects are accordingly achieved by methods for the continuous treatment of multiphase fluid streams, as defined in the claims, or by rotating separators and uses as disclosed below. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0016] Those features of inventive objects that are designated as preferred below are combined in particularly preferred embodiments with other features designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature designated as preferred to any extent is combined with one or more further features designated as preferred to any extent. Features of preferred rotating separators and uses emerge from the features of preferred methods.

[0017] The invention relates to a method for the continuous treatment of multiphase fluid streams during the operation of fuel cells, comprising the steps: a) Providing a multiphase fluid stream comprising a gaseous phase and a liquid phase, wherein the gaseous phase comprises a carrier substance and a process substance, wherein the liquid phase comprises the process substance, wherein the process substance is water, b) Introducing the multiphase fluid stream into a continuously operable rotating separator, wherein the rotating separator is preferably operated continuously or at intervals, particularly preferably continuously, c) At least partially separating the liquid phase from the multiphase fluid stream by means of the rotating separator to produce a treated fluid stream comprising a treated gas phase, wherein 98 wt.% or more of the liquid phase is separated, wherein the treated gas phase comprises the carrier substance and the process substance, wherein the molar fraction of the process substance in the treated gas phase is 50 % or more of the mole fraction of the process material in the gaseous phase of the multiphase fluid stream.

[0018] The method according to the invention is intended for use in the operation of fuel cells, in particular polymer electrolyte fuel cells, i.e., fuel cells that use a polymer membrane as the electrolyte. In this case, the use of the method according to the invention in the anode-side fluid line system of the fuel cell is preferred.

[0019] However, the inventors of the present invention have come to the conclusion that the knowledge gained during the optimization for the fuel cell regarding the continuous processing of multiphase fluid streams using a rotating separator is also fundamentally relevant for other areas of application not according to the invention which require careful control of the process material concentration in a gas phase because, for example, downstream devices and elements require a certain minimum amount of process material.

[0020] In step a) of the process according to the invention, a multiphase fluid stream is provided, comprising a gaseous and a liquid phase. A corresponding multiphase fluid stream can be formed, for example, in a fuel cell, in which water is formed by the redox reaction, which is discharged from the fuel cell in condensed form together with the excess fuel.

[0021] From the inventors' point of view, it is fundamentally possible for the multiphase fluid stream to also include a solid phase, for example, particulate contaminants, in certain applications. However, this is less preferred for most applications and should generally be avoided, especially in the operation of fuel cells. In any case, it can be considered an advantage of the method according to the invention that any particulate contaminants present in the fluid stream can be automatically and thoroughly separated using a rotating separator.

[0022] The multiphase fluid stream to be provided according to the invention comprises a process substance in the liquid phase. Within the scope of the present invention, this process substance is the compound whose concentration must be carefully controlled in the process according to the invention. According to the invention, particularly in the preferred use of the process according to the invention in a polymer electrolyte fuel cell, the process substance will be water.

[0023] In addition to the liquid phase, the process material also exists in the gaseous phase, whereby, depending on the temperature and the prevailing pressure, a phase equilibrium between the process material in the gaseous and the liquid phase will regularly be established or whereby the multiphase system will at least strive towards this state.

[0024] In addition to the gaseous process material, the gaseous phase also comprises the carrier material. Simply put, the term "carrier material" refers to all gaseous components other than the process material. In the process according to the invention, the carrier material primarily serves to provide a sufficient gas volume and to enable transport of the process material in liquid and gaseous form through a fluid line system. In practice, particularly in the application according to the invention in fuel cells, the carrier material will usually be the fuel supplied in excess of stoichiometric amounts or a mixture containing the fuel, for example in combination with nitrogen.

[0025] In accordance with the above, the provided multiphase fluid stream is introduced into a continuously operable rotating separator in step b) of the process according to the invention. Continuously operable rotating separators are generally known to those skilled in the art from other fields of application and differ from other rotating separators that cannot be operated continuously, for example, centrifuges. Those skilled in the art refer to rotating separators as separators that have one or more elements whose rotation causes or promotes a separation effect.

[0026] By means of this rotating separator, the liquid phase, i.e. the phase which comprises the liquid process material, is at least partially separated from the multiphase fluid stream in step c), wherein a substantial separation of 98 wt.% or more of the liquid phase, preferably 99 wt.% or more of the liquid phase, is according to the invention.

[0027] This step c) results in a treated fluid stream comprising at least one treated gas phase. In light of the above, it is understandable that this treated fluid stream can potentially comprise a liquid and a gaseous phase, so that the treated fluid stream can also be a multiphase system, which may even be particularly preferred in some cases, as disclosed below.

[0028] It is now important for the process according to the invention that the prepared gas phase contains not only the carrier substance, but also the process substance, ie the process substance in gaseous form. According to the inventors, it is essential that the molar fraction of the process substance in the prepared gas phase, iethe gas phase of the treated fluid stream, as it emerges from the continuously operable rotating separator, is not reduced too much despite the performance of the rotating separator, whereby halving the molar fraction of the process substance in the gaseous phase compared to the molar fraction of the same process substance in the gaseous phase of the multiphase fluid stream could be identified as a reasonable limit value with which excellent performance could be achieved, particularly in the operation of polymer electrolyte fuel cells over a wider parameter range and under a wide variety of operating conditions.

[0029] It has proven particularly advantageous to operate the process according to the invention in such a way that the differences in the relative composition of the conditioned gas phase compared to the gaseous phase of the multiphase fluid stream are as small as possible. This allows, in particular, fuel cells which are operated at low load and in which comparatively little water is produced to be operated reliably even over longer periods of time, wherein the fluid flow in the fluid line system can be provided with the necessary pressure by the rotating separator. A process according to the invention is therefore preferred in which the molar fraction of the process material in the conditioned gas phase is 80% or more, preferably 90% or more, particularly preferably 95% or more, very particularly preferably 95 to 105%, of the molar fraction of the process material in the gaseous phase of the multiphase fluid stream.

[0030] This relationship between the composition of the gas phase before and after the rotating separator can, in accordance with the expert understanding, also be expressed via the ratio of the partial pressures between the carrier substance and the process substance. Alternatively, a process according to the invention is thus preferred, wherein the ratio of the partial pressure of the process substance to the partial pressure of the carrier substance from the gaseous phase of the multiphase fluid stream to the conditioned gas phase is reduced by 50% or less. Analogously, a process according to the invention is preferred, wherein the ratio of the partial pressure of the process substance to the partial pressure of the carrier substance from the gaseous phase of the multiphase fluid stream to the conditioned gas phase is reduced by 20% or less, preferably 10% or less, more preferably 5% or less, most preferably essentially not at all.

[0031] To determine the change in molar mass of the process material in the gas phase upstream and downstream of the rotating separator, the person skilled in the art can resort to common determination methods, selecting a suitable method depending on the process parameters, in particular depending on the process material. For organic process materials, the person skilled in the art can, for example, take samples and analyze them using gas chromatography. For the inventive case of water as the process material, the determination can be carried out, for example, using a conventional hygrometer; in preferred embodiments, a hygrometer can be placed upstream and downstream of the rotating separator. Depending on the selected measurement method, it is also expedient to determine the total pressure of the gas phase, for example to calculate the partial pressure of the process material.

[0032] In accordance with the expert understanding, the determination of the molar fractions or the partial pressures is carried out under the process conditions, ie at the temperature and pressure prevailing during operation of the process according to the invention.

[0033] The molar fractions or partial pressures are clearly defined at all times and are not dependent on the measurement method, which only affects the accuracy of the determination. The expert is therefore free to choose the measurement method used, especially if the determined change is so far from the defined limit that it cannot be reached even when taking measurement error into account. The expert will usually only need to resort to a more precise measurement method if the distance from the defined limit is equal to the measurement uncertainty.

[0034] The inventors of the present invention have identified various options with which the maximum change in the molar fraction of the process material in the gas phase to be set in the process according to the invention, as well as the preferred values ​​for this change, can be realized. According to the inventors of the present invention, the particular aim is to prevent condensation of the process material contained in the gas phase in the rotating separator, which would reduce the molar fraction of this process material in the gas phase, or at least to reduce its extent by means of suitable design and process engineering measures. This represents a particular challenge because the rotating separator at least partially removes the liquid phase of the multiphase fluid stream from equilibrium, thereby promoting condensation.

[0035] In the processes known from the state of the art other than the fuel cell, which are operated using a rotating separator, this problem is hardly relevant, since in these applications it is usually preferred if the condensed process material can be separated as completely as possible with the other parts to be removed.

[0036] The options identified by the inventors of the present invention for controlling the partial pressure change, which are listed below, can, in the opinion of the inventors of the present invention, be suitably selected and combined by a person skilled in the art to obtain a method compatible with the setup used by the person skilled in the art. From the inventors' point of view, it has proven particularly advantageous to combine two or more, preferably three or more, particularly preferably four or more of the options described below, with very particular preference being given to using all of the options described below.

[0037] Many of the rotating separators used in the prior art, which are designed to purify a gas stream as completely as possible, have elements that serve to physically and chemically bind water, for example, drying agents or refrigeration dryers. However, in the opinion of the inventors, the rotating separator to be used in the process according to the invention should not comprise any of these elements. Thus, a process according to the invention is preferred in which the rotating separator does not comprise any means for removing the gaseous process substance from the gas phase, in particular by chemical binding and / or adsorption of the process substance. This configuration also has the advantage that corresponding rotating separators are less maintenance-intensive and there is no need to replace the drying agent from time to time.

[0038] In addition to dispensing with specific devices for drying the gas phase, the inventors of the present invention have identified a particularly efficient way of influencing the change in the amount of substance. In principle, it would be intuitively desirable to separate the liquid phase in the multiphase fluid stream as much as possible in order to achieve the lowest possible mass fraction of the liquid phase in the treated fluid stream of 1% or less, preferably 0.5% or less, particularly preferably 0.1% or less, which may also be preferred for certain applications.

[0039] However, the inventors of the present invention have recognized that unwanted condensation of the gaseous process material from the gas phase can be particularly effectively avoided if the liquid phase is not completely removed from the fluid stream, despite the potentially high performance of the rotating separator, so that even the treated fluid stream still contains residues of the liquid phase that are in equilibrium with the gas phase. This process can advantageously be adjusted particularly easily, namely by specifically controlling the performance of the rotating separator or its inherent separation efficiency for water. It has proven particularly effective in this regard if the remaining portion of condensed process material in the liquid phase is present in the form of small particles with an average droplet size of 1 µm or less.

[0040] The inventors of the present invention have identified particularly suitable ranges for the described conflict of objectives between the most extensive possible separation and the retention of a liquid phase to ensure the smallest possible change in the molar fraction of the process material, with which the process according to the invention can be operated particularly advantageously, in particular in the operation of a polymer electrolyte fuel cell. A process according to the invention is preferred, wherein the separation in step c) is carried out such that the treated fluid stream comprises the liquid phase in a mass fraction of 0.05 to 2%, preferably 0.1 to 1%, particularly preferably 0.2 to 0.5%, based on the mass of the treated fluid stream.

[0041] In the course of considering how to prevent the unwanted separation of the process material from the gas phase, the inventors of the present invention recognized that the temperature of the rotating separator can advantageously be adjusted in order to reduce the extent of unwanted condensation in the rotating separator. In accordance with the expert understanding, the temperature of the inner walls of the working chamber, i.e. the space through which the multiphase fluid flow is passed, is relevant here. Particularly in combination with targeted power control to adjust a residual liquid phase content, this procedure has proven to be an excellent solution for providing a conditioned fluid flow which enables long-term, fault-free operation, for example in a fuel cell with a polymer electrolyte membrane.For easier handling, it is possible to cover the rotating separator externally with thermal insulation, which is preferred for many applications. It is particularly preferred to equip the rotating separator with a heating device so that the temperature of the rotating separator can be controlled during the process. Thus, a method according to the invention is preferred, wherein the rotating separator has a temperature of 60°C or more, preferably 70°C or more, particularly preferably 80°C or more, on the inner walls of the working chamber.

[0042] Particularly in combination with a temperature-controlled rotating separator and / or when using heated fluid streams, it has also proven advantageous to provide a reservoir of the liquid process material in the rotating separator, the gas space of which is in fluid communication with the working chamber. This makes it possible to enable additional saturation of the gas phase with the process material via the preferably temperature-controlled liquid in the reservoir, which counteracts unwanted condensation. Advantageously, this reservoir can be fed directly from the separated liquid phase. This embodiment has also proven particularly advantageous because it enables a minimum degree of saturation of the gas phase with the process material.

[0043] According to the inventors, a further option for controlling the change in the molar fraction of the process material in the gaseous phase consists in the appropriate selection of the type of rotating separator. Due to their general operating principle, a specific selection of rotating separators makes it easier to avoid excessive changes in the molar fraction of the process material, or the process parameters can be particularly easily adjusted to counteract excessive changes. In this respect, a method according to the invention is preferred, wherein the rotating separator is a turbomachine, a rotating filter, a rotating channel separator, or a disc separator, with the rotating separator preferably being a disc separator.Disc separators are also preferred because they can regularly be operated particularly energy-efficiently, so that the method according to the invention is energy-saving compared to the prior art.

[0044] Of the rotating separators described above, the use of a disc separator is particularly preferred according to the findings of the inventors of the present invention. Especially when a disc separator is used in the fluid line systems of a fuel cell with a polymer electrolyte membrane, the method according to the invention can be operated particularly advantageously, especially because disc separators are well suited to ensuring a continuous fluid flow.

[0045] According to the inventors of the present invention, the use of a disc separator is also advantageous because it allows the degree of unwanted condensation of the process material from the gas phase to be particularly well controlled through design measures. The inventors have recognized that it is particularly advantageous not to select an excessively large distance between the discs of the disc separator. A preferred method according to the invention is one in which the rotating separator is a disc separator, the distance between the discs being less than 0.6 mm, preferably less than 0.3 mm, and particularly preferably less than 0.2 mm.

[0046] In addition, the inventors propose using discs with particularly smooth surfaces to reduce unwanted condensation, which can be achieved, for example, by a suitable surface treatment during the manufacturing process. Without wishing to be bound by this theory, the inventors of the present invention assume that the particularly smooth surfaces act as condensation nuclei to a lesser extent, thereby reducing the extent of condensation. Thus, a method according to the invention is preferred, wherein the rotating separator is a disc separator, wherein the discs have an average roughness depth Rz according to DIN EN ISO 1302:2002 of 25 µm or less, preferably 10 µm or less, particularly preferably 6.3 µm or less.

[0047] In the eyes of the inventors of the present invention, it has proven particularly advantageous, in contrast to conventional designs in the prior art, to form the plates from a material that repels the process substance or to coat the surface with a corresponding material. In the case of water as the process substance according to the invention, this can be, for example, a hydrophobic material, such as polytetrafluoroethylene or other perfluorocarbon compounds. Without wishing to be bound by this theory, the inventors of the present invention assume that such repellent surfaces allow only a lower degree of condensation of the process substance.Accordingly, a method according to the invention is preferred, wherein the rotating separator is a disc separator, wherein at least one of the discs, preferably all of the discs, particularly preferably all of the components of the disc separator that are in contact with the fluid flow, consist of a material that repels the process substance or are coated with a material that repels the process substance, wherein the process substance on the material that repels the process substance has a contact angle in the range of 70° or more, preferably 80° or more, particularly preferably 90° or more, very particularly preferably 100° or more.

[0048] Furthermore, in the inventors' view, it is sensible to avoid cooling of the gas through expansion, which could promote condensation of the process material from the gas phase. The inventors of the present invention accordingly propose designing and operating the rotating separator in such a way that an isenthalpic pressure reduction does not occur, which could lead to cooling via the Joule-Thomson effect. Accordingly, a method according to the invention is preferred, wherein the difference in total pressure between the gaseous phase of the multiphase fluid stream upstream of the rotating separator and the conditioned gas phase of the conditioned fluid stream downstream of the rotating separator is less than 1%, preferably less than 0.5%, particularly preferably less than 0.1%.

[0049] The process according to the invention can advantageously be carried out in such a way that the separated liquid phase and / or the treated gas phase from the process can be recycled to the working device used to provide the multiphase fluid stream. The corresponding process according to the invention can thus be operated in a circuit, in particular a closed circuit.

[0050] In this case, it is possible, for example, to feed the separated liquid phase to a working device in which the multiphase fluid stream provided in step a) is generated. This can be, for example, steam engines or similar devices. In this respect, a method according to the invention is preferred, wherein the liquid phase separated in step c) is at least partially fed to a working device in which the multiphase fluid stream provided in step a) is generated.

[0051] However, the procedure described above is generally not desirable for use in the operation of fuel cells. In fuel cells, however, the removed liquid phase should be fed to a discharge system with which the separated liquid phase is removed from the fuel cell system in order to prevent undesired flooding of the fuel cell. However, when used in a fuel cell, as explained above, it is particularly advantageous and expedient to return the conditioned fluid stream generated in step c) to the fuel cell. Consequently, a method according to the invention is preferred, wherein the conditioned fluid stream generated in step c) is at least partially fed to a working device in which the multiphase fluid stream provided in step a) is generated.In light of the above, it is clear that such a method according to the invention is preferred, wherein the working device is a fuel cell, in particular a polymer electrolyte fuel cell.

[0052] The inventors of the present invention have recognized that it can be particularly challenging to operate the process according to the invention at very low and very high temperatures, especially in the inventive combination with a fuel cell. In this case, it is particularly challenging to control the change in the molar fraction of the process material in the gaseous component according to the invention in extreme temperature ranges. Accordingly, the inventors of the present invention propose certain temperature ranges in which the process according to the invention can be carried out particularly effectively. Against this background, a process according to the invention is preferred, wherein the multiphase fluid stream and / or the conditioned fluid stream has a temperature in the range from -40 to 120 °C, preferably in the range from 0 to 110 °C.

[0053] As explained above, it is considered a particularly advantageous aspect of the present invention if the change in the molar fraction of the process material in the gas phase is controlled via the power of the rotating separator, in which the separator deliberately allows a certain portion of the liquid phase to pass through. For this purpose, it has proven particularly advantageous to equip the rotating separator with an electric motor so that it can be controlled via the power of the electric motor. A method according to the invention is therefore preferred, wherein the rotating separator is driven by an electric motor, wherein the electric motor is preferably installed in a capsule that is permeable to the carrier material and / or the process material, wherein the conveying capacity and / or the separation capacity of the rotating separator can preferably be controlled via the power of the electric motor.

[0054] As explained above, it is advantageous to operate the rotating separator in such a way that a small portion of the liquid phase remains in the treated fluid stream. However, this can be associated with problems during further use of the fluid stream. For example, it is possible that the process material condenses upstream of the rotating separator and deposits on the walls of the fluid line system. Such deposits can be carried along by the fluid flow, resulting in unexpected fluctuations in the liquid input into the rotating separator, which could then lead to an undesirably high proportion of liquid phase in the treated fluid stream. To prevent this, simpler, non-rotating pre-separators can be provided to prevent the entry of such condensates into the rotating separator.Accordingly, a method according to the invention is preferred, wherein the multiphase fluid stream is passed through a, preferably non-rotating, pre-separator before being introduced into the continuously operable rotating separator.

[0055] Depending on the design of the fluid line system, further condensation may also occur downstream of the rotating separator. Likewise, it cannot be ruled out that the liquid phase content may still be too high for certain applications after passing through the rotating separator. In these cases, the use of a secondary separator is recommended, which can advantageously be arranged directly upstream of the inlet of the working device in order to reduce the liquid phase content to the desired level in case of doubt. Thus, a method according to the invention is preferred, wherein the treated fluid stream is passed through a, preferably non-rotating, secondary separator.

[0056] Based on the collected findings and the basic inventive idea, the inventors of the present invention were able to identify specific operating parameters with which the method according to the invention can be operated particularly advantageously.

[0057] A method according to the invention is preferred, wherein the rotating separator has a separation efficiency of 70% or more, preferably 80% or more, particularly preferably 90% or more, with respect to liquid particles having a diameter of less than 1 µm.

[0058] Also preferred is a method according to the invention, wherein the multiphase fluid stream is an aerosol, wherein the liquid phase in the multiphase fluid stream is preferably present as liquid particles with a diameter d50 of less than 10 µm, preferably less than 5 µm, particularly preferably less than 2 µm.

[0059] From the inventors' point of view, those processes according to the invention are particularly advantageous in which the gaseous phase comprises a multi-component system as a carrier substance, wherein it is particularly advantageous with regard to the efficiency of the process if the carrier substance used dissolves as little as possible in the liquid phase of the multiphase fluid stream. Preference is therefore given to a process according to the invention in which the gaseous phase comprises two or more different substances as a carrier substance. Preference is also given to a process according to the invention in which the combined mass fraction of all carrier substances in the liquid phase of the multiphase fluid stream is less than 5%, preferably less than 3%, particularly preferably less than 1%, based on the mass of the liquid phase of the multiphase fluid stream.

[0060] The inventors of the present invention were also able to identify particularly suitable carriers. A preferred method according to the invention is one in which the carrier is selected from the group consisting of helium, neon, argon, nitrogen, oxygen, hydrogen, and mixtures of these substances, with the carrier preferably being selected from the group consisting of nitrogen, hydrogen, and mixtures of these substances.

[0061] For the use of the process according to the invention in the operation of fuel cells, the inventors were also able to identify a particularly suitable mixture for the carrier substance. In this case, a process according to the invention is preferred, wherein the carrier substance in the gaseous phase of the multiphase fluid stream comprises hydrogen with a mass fraction of 30 to 100%, preferably a mass fraction of 50 to 95%, and nitrogen with a mass fraction of 0 to 70%, preferably a mass fraction of 5 to 50%, based on the mass of the gaseous phase.

[0062] In light of the above, it is apparent to those skilled in the art that the method according to the invention is intended for use in fuel cells, in particular polymer electrolyte fuel cells, and in this respect, above all, in their anode-side fluid line system or fluid management system. For this intended use, the relevant process substance, the concentration of which should be specifically controlled, is water. Consequently, a method according to the invention is according to the invention, wherein the process substance is water. In this context, a method according to the invention is also particularly preferred, wherein the multiphase fluid stream in step a) is generated by a working device, wherein the working device is preferably a fuel cell, in particular a polymer electrolyte fuel cell.

[0063] For the process material water and the operation of a polymer electrolyte fuel cell, the inventors were able to identify a particularly suitable range of absolute molar fractions in the treated gas stream. A process according to the invention is preferred, wherein the molar fraction of the process material in the treated gas phase is in the range of 10 to 40%, preferably 13 to 35%, particularly preferably 16 to 30%.

[0064] In light of the above explanations, the person skilled in the art will recognize that the invention also relates to a rotating separator. The invention thus also relates to a rotating separator for use in a process according to the invention, wherein the rotating separator is continuously operable, wherein the rotating separator is configured to at least partially separate the liquid phase of a multiphase fluid stream comprising a process substance from the gaseous phase comprising a carrier substance and the process substance, such that the resulting conditioned gas phase comprises the carrier substance and the process substance and such that the molar fraction of the process substance in the conditioned gas phase is 50% or more of the molar fraction of the process substance in the gaseous phase of the multiphase fluid stream.

[0065] The rotating separator according to the invention is particularly preferred because it allows the method according to the invention to be implemented particularly efficiently. Preferred embodiments of the rotating separator according to the invention are described below, which serve to implement preferred methods according to the invention and can therefore be considered particularly advantageous.

[0066] A rotating separator according to the invention is preferred, wherein the rotating separator is a turbomachine, a rotating filter, a rotating channel separator or a disc separator, wherein the rotating separator is preferably a disc separator.

[0067] A rotating separator according to the invention is also preferred, wherein the rotating separator comprises a heating device for tempering the inner walls of the working chamber.

[0068] Also preferred is a rotating separator according to the invention, wherein the rotating separator is a disc separator, wherein the distance between the discs is less than 0.6 mm, preferably less than 0.3 mm, particularly preferably less than 0.2 mm.

[0069] Also preferred is a rotating separator according to the invention, wherein the rotating separator is a disc separator, wherein the discs have an average roughness depth Rz of 25 µm or less, preferably 10 µm or less, particularly preferably 6.3 µm or less. Also preferred is a rotating separator according to the invention, wherein the rotating separator is a disc separator, wherein at least one of the discs, preferably all of the discs, particularly preferably all of the components of the disc separator that are in contact with the fluid flow consist of a material that repels the process substance or are coated with a material that repels the process substance, wherein the process substance on the material that repels the process substance has a contact angle in the range of 70° or more, preferably 80° or more, particularly preferably 90° or more, very particularly preferably 100° or more.

[0070] Also preferred is a rotating separator according to the invention, comprising a non-rotating pre-separator and / or a non-rotating post-separator.

[0071] Furthermore, a rotating separator according to the invention is preferred, wherein the rotating separator has a separation efficiency of 70% or more, preferably 80% or more, particularly preferably 90% or more, with respect to liquid particles having a diameter of less than 1 µm.

[0072] Also disclosed in connection with the invention is the use of such a rotating separator for the continuous processing of multiphase fluid streams during the operation of fuel cells, in particular polymer electrolyte fuel cells, for extending the service life of a fuel cell when operated at a power which is less than 20%, preferably less than 10%, of the maximum power.

[0073] Finally, the invention also relates to a fuel cell system, in particular a polymer electrolyte fuel cell system, comprising a fluid line system for supplying fluid to at least one electrode of a fuel cell, in particular the anode, wherein such a rotating separator for the continuous processing of multiphase fluid flows is provided in at least one fluid line.

[0074] A corresponding fuel cell system according to the invention is advantageous because it allows the method according to the invention to be carried out and the fuel cell can be operated for extended periods even at low loads, preventing the electrolyte membrane from drying out. Furthermore, the rotating separator advantageously makes it possible to supply the fuel cell with sufficient recycled fuel even at low loads and correspondingly low power levels. This advantageously achieves high operational reliability and a long service life.

[0075] The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figure. The figure shows: Fig. 1 is a schematic representation of a rotating separator according to the invention in a particularly preferred embodiment, with which the method according to the invention can be carried out in preferred embodiments.

[0076] Fig. 1 shows a schematic representation of a rotating separator according to the invention in a particularly preferred embodiment.

[0077] The rotating separator 10 shown is suitable and intended for use in a process according to the invention. The rotating separator 10 is a continuously operable disc separator.

[0078] The rotating separator 10 according to Fig. 1 is arranged in the anode-side fluid line system of a polymer electrolyte fuel cell system (not shown) and serves for the continuous processing of multiphase fluid streams, in particular comprising hydrogen and water.

[0079] In the Fig. 1 In the example shown, the rotating separator 10 is configured to at least partially separate the liquid phase of a multiphase fluid stream, which primarily comprises water, from the gas phase comprising hydrogen, water, and optionally nitrogen. This can advantageously be achieved with the rotating separator 10 according to the invention such that the resulting conditioned gas phase comprises hydrogen and water, and the molar fraction of water in the conditioned gas phase is 50% or more of the molar fraction of water in the gaseous phase of the multiphase fluid stream, i.e., before conditioned treatment.

[0080] The multiphase fluid flow enters the rotating separator 10 from below, indicated by the solid arrow. A conveying device located below the working chamber 16 conveys the fluid through the rotating separator 10. The rotating separator 10 comprises a disk stack consisting of several disks 12, which are driven in rotation by an electric motor 14. The electric motor 14 allows the separation efficiency to be adjusted. Separation occurs through the disk stack, with the separated liquid phase being discharged at the right edge in the example shown, which is indicated by a solid arrow.

[0081] The processed gas phase, which includes not only the carrier substance hydrogen but also gaseous water, is led away to the left in the schematic representation and recycled to the fuel cell.

[0082] The rotating separator 10 according to Fig. 1includes a heating device (not shown) for tempering the inner walls of the working chamber 16 and has a distance of 0.25 mm between the plates 12. The average surface roughness of the plates 12 is 6.3 µm. The plates 12 of the rotating separator 10 are made of polytetrafluoroethylene, and the inner walls of the working chamber 16 are coated with polytetrafluoroethylene.

[0083] The exemplary rotating separator 10 according to Fig. 1 has a separation efficiency of 70% or more with respect to liquid particles with a diameter of less than 1 µm. Reference symbol

[0084] 10Rotating separator 12Disk 14Electric motor 16Working chamber

Claims

1. Method for continuously treating multiphase fluid flows during operation of fuel cells, comprising the steps of: a) providing a multiphase fluid flow comprising a gas phase and a liquid phase, wherein the gas phase comprises a carrier substance and a process substance, wherein the liquid phase comprises the process substance, wherein the process substance is water, b) introducing the multiphase fluid flow into a continuously operable rotating separator (10), c) at least partially separating the liquid phase from the multiphase fluid flow by means of the rotating separator (10) to produce a treated fluid flow comprising a treated gas phase, wherein 98 wt.% or more of the liquid phase are separated, wherein the treated gas phase comprises the carrier substance and the process substance, wherein the molar fraction of the process substance in the treated gas phase is 50 % or more of the molar fraction of the process substance in the gas phase of the multiphase fluid flow.

2. Method according to claim 1, wherein the separation in step c) is carried out in such a way that the treated fluid stream comprises the liquid phase in a mass fraction of 0.05 to 2 %, preferably 0.1 to 1 %, particularly preferably 0.2 to 0.5 %, relative to the mass of the treated fluid stream.

3. Method according to any of claims 1 or 2, wherein the rotating separator (10) at the inner walls of the working chamber (16) has a temperature of 60 °C or more, preferably 70 °C or more, particularly preferably 80 °C or more.

4. Method according to any of claims 1 to 3, wherein the rotating separator (10) is a turbo machine, a rotating filter, a rotating channel separator or a disk separator, wherein the rotating separator (10) is preferably a disk separator.

5. Method according to claim 4, wherein the rotating separator (10) is a disk separator, wherein the disks (12) have an average roughness depth Rz of 25 µm or less, preferably 10 µm or less, particularly preferably 6.3 µm or less.

6. Method according to any of claims 4 or 5, wherein the rotating separator (10) is a disk separator, wherein the distance between the disks (12) is less than 0.6 mm, preferably less than 0.3 mm, particularly preferably less than 0.2 mm.

7. Method according to any of claims 4 to 6, wherein the rotating separator (10) is a disk separator, wherein at least one of the disks (12), preferably all disks (12), particularly preferably all components of the disk separator which are in contact with the fluid flow, consist of a material which repels the process substance or are coated with a material which repels the process substance, wherein the process substance has a contact angle on the material which repels the process material of 90° or more, preferably 100° or more.

8. Method according to any of claims 1 to 7, wherein the rotating separator (10) is driven by an electric motor (14), wherein the electric motor (14) is preferably installed in a capsule that is impermeable to the carrier substance and / or the process substance, wherein the delivery capacity and / or the separation capacity of the rotating separator (10) can preferably be controlled by the power of the electric motor (14).

9. Rotating separator (10) for use in a method according to any of claims 5 to 8, wherein the rotating separator (10) can be operated continuously, wherein the rotating separator (10) is configured to at least partially separate the liquid phase of a multiphase fluid flow comprising a process substance from the gas phase comprising a carrier substance and the process substance, so that the obtained treated gas phase comprises the carrier substance and the process substance, and so that the molar fraction of the process substance in the treated gas phase is 50 % or more of the molar fraction of the process substance in the gas phase of the multiphase fluid flow, wherein the rotating separator (10) is a disk separator, and wherein the disks (12) have an average roughness depth Rz of 25 µm or less.

10. Fuel cell system, in particular a polymer electrolyte fuel cell system, comprising a fluid line system for the fluid supply for at least one electrode of a fuel cell, in particular the anode, wherein a rotating separator according to claim 9 is provided in at least one fluid line for continuously treating multiphase fluid flows.