Method for operating a stack arrangement and stack arrangement

Abstract

The invention relates to a method for operating a stack arrangement comprising at least one stack (2) and a housing (3) accommodating the at least one stack (2), wherein the housing (3) encloses a gas-filled volume (4) which, for gas exchange, is connected via a gas inlet (5) to an inlet line (6) and via a gas outlet (7) to an outlet line (8). According to the invention, by opening a valve (10) integrated into a recirculation line (9), a gas or gas mixture is discharged from the volume (4) and reintroduced into the volume (4) via the recirculation line (9) and the gas inlet (5). The invention further relates to a stack arrangement (1) which is suitable for carrying out the method according to the invention.

Description

[0001] The present invention relates to a method for operating a stack arrangement according to the preamble of claim 1. Furthermore, the invention relates to a stack arrangement which is suitable for carrying out the method.

[0002] The preferred field of application of the invention is electrochemical systems, in particular electrolysis systems for producing hydrogen or hydrogen-based fuel cell systems. The at least one stack of the stack arrangement can therefore be, in particular, an electrolysis stack or a fuel cell stack. State of the art

[0003] The stack is the heart of an electrochemical system, regardless of whether the system is an electrolysis system or a fuel cell system. The electrochemical reaction for material conversion takes place in the stack, or rather in the electrochemical cells that form the stack.

[0004] In an electrolysis stack, for example, an electrochemical reaction takes place in which water is split into hydrogen and oxygen. Various technologies can be used, such as proton exchange membranes (PEM), anion exchange membranes (AEM), alkaline electrolysis (AEL), or solid oxide electrolyzer cells (SOEC). They all have in common that the produced hydrogen can accumulate in areas outside the stack due to leaks and / or diffusion. Since hydrogen can form an explosive gas mixture with air or oxygen, the stack is enclosed - individually or in combination with at least one other stack. The enclosure can also accommodate components for the media supply and power supply of the stack(s), such as cables, sensors, or actuators.If the electrochemical plant's power electronics are located near the enclosure, they are ideally housed in a separate enclosure to prevent arcing.

[0005] Since hydrogen can not only escape to the outside but also accumulate inside the enclosure, the interior is usually constantly actively ventilated. This constant active ventilation leads to a continuous air exchange and thus a dilution of the leaked hydrogen. This ensures that the hydrogen concentration inside the enclosure does not exceed a safety-relevant limit.

[0006] Constant active ventilation of the enclosure's interior also provides cooling. This prevents the enclosure's interior from overheating due to the waste heat from at least one stack.

[0007] Constant active ventilation requires a high air turnover and therefore considerable effort. Depending on the ambient conditions, particularly the ambient temperatures, at the installation location of the stack arrangement, prior cooling of the air used for ventilation may also be necessary. This is often the case in hot countries, for example. Furthermore, due to unfavorable ambient conditions, air conditioning in the form of purification may be necessary.

[0008] The present invention is concerned with the task of reducing the effort and costs involved in ventilating an enclosed stack arrangement.

[0009] To achieve this object, the method having the features of claim 1 and the stack arrangement having the features of claim 7 are specified. Advantageous further developments of the invention can be found in the respective subclaims. Disclosure of the invention

[0010] A method is proposed for operating a stack arrangement comprising at least one stack and a housing accommodating the at least one stack. The housing encloses a gas-filled volume, which is connected to an inlet line via a gas inlet and to an outlet line via a gas outlet for gas exchange. According to the invention, by opening a valve integrated into a recirculation line, a gas or gas mixture is discharged from the volume and reintroduced into the volume via the recirculation line and the gas inlet.

[0011] The proposed method recirculates a gas or gas mixture from the gas-filled volume of the enclosure, thus reducing gas consumption. This means that less fresh gas needs to be introduced into the volume via the inlet line. The gas can, in particular, be air, which is introduced into the volume for ventilation. By recirculating gas or air discharged via the gas outlet, the amount of required and, if necessary, treated fresh air can be significantly reduced.

[0012] The removal of released hydrogen from the volume is further ensured, as not only recirculated gas but also fresh gas or fresh air can be introduced into the volume via the gas inlet. Suitable sensors can monitor whether the hydrogen concentration reaches critical levels, in which case recirculation must be interrupted. The gas or gas mixture released from the volume is then completely discharged via the outlet line.

[0013] The recirculation of the gas or gas mixture can be achieved passively using a gas flow introduced into the volume via the inlet line and the gas inlet, and / or actively using a blower integrated into the recirculation line. The first variant has the advantage that the effort required to recirculate the gas or gas mixture is minimal. Furthermore, energy can be saved. The second variant has the advantage that recirculation is more easily controllable; in particular, it can be carried out independently of the gas flow in the inlet line. This means that only recirculated gas can be introduced into the volume.

[0014] In a further development of the invention, it is proposed that the recirculated gas or gas mixture be passed through a hydrogen filter before being reintroduced into the volume. This means that the hydrogen contained in the recirculated gas is completely or at least partially removed. The necessary ventilation of the volume can thus be achieved – at least temporarily – solely with the aid of the recirculated gas. The need for fresh gas or fresh air can thus be further reduced.

[0015] The hydrogen filter can be implemented in various ways. For example, a filter with a palladium membrane can be used. The gas or gas mixture discharged from the volume and recirculated heats the palladium membrane, allowing it to reliably remove the hydrogen contained in the gas or gas mixture. Alternatively, the filter can be implemented using a recombination catalyst with a downstream gas dryer, where the gas dryer can be designed as a cold trap or silicate dryer. This variant of the hydrogen filter has the advantage that the water content can be determined through monitoring and used for control purposes.

[0016] Furthermore, it is proposed that the recirculated gas or gas mixture be tempered, preferably cooled, before being reintroduced into the volume. Ventilation of the stack arrangement can thus simultaneously achieve effective cooling. Cooling of the recirculated gas can be achieved, for example, using a heat exchanger integrated into the recirculation line.

[0017] The valve integrated into the recirculation line can be opened on a time-controlled basis and / or depending on the gas composition in the volume and / or depending on the gas composition of the recirculate. For example, fixed time intervals can be defined in which the valve is opened and the discharged gas or gas mixture is recirculated. Opening the valve depending on the gas composition in the volume and / or the gas composition of the recirculate enables demand-based control of recirculation. However, knowledge of the gas composition is a prerequisite, so this variant requires a gas sensor, particularly a hydrogen sensor. During recirculation, the amount of hydrogen in the recirculate is measured, and this value can then be used, for example, to shut down recirculation.

[0018] Advantageously, recirculation is only operated in stable, predefined operating states. In other cases, especially during a change of operating states (start-up -> operation, operation -> standby, operation -> off), the valve integrated into the recirculation line is kept closed. If a fan for active recirculation is present, a decision can be made whether ventilation should be achieved exclusively through recirculation or exclusively through the introduction of fresh gas or fresh air. Ventilation via recirculation in combination with fresh gas or fresh air is also possible and does not require a fan.

[0019] As a further development, it is proposed that an inert gas, preferably nitrogen, be introduced into the volume via the inlet line. This achieves at least partial inerting of the atmosphere inside the enclosure. The introduced inert gas reduces the air content in the volume, allowing higher hydrogen contents without the formation of an explosive gas mixture. Accordingly, the gas flow rates can be reduced.

[0020] In combination with the proposed recirculation, the amount of inert gas introduced into the enclosure for ventilation can be kept low, further reducing the effort and costs involved. Furthermore, both the inlet and outlet lines can be smaller.

[0021] To achieve the aforementioned object, a stack arrangement for an electrochemical system, in particular an electrolysis system or a fuel cell system, is further proposed. The stack arrangement comprises at least one stack and a housing accommodating the at least one stack. The housing encloses a volume that is connected to an inlet line via a gas inlet and to an outlet line via a gas outlet. A connection between the gas outlet or the outlet line and the gas inlet or the inlet line can be established via a recirculation line with an integrated valve.

[0022] The proposed stack arrangement is particularly suitable for carrying out the method according to the invention described above, or can be operated according to this method, so that the same advantages can be achieved. In particular, effective gas exchange within the volume of the enclosure can be achieved with little effort and at low cost.

[0023] The recirculation line can be connected to the gas outlet directly or indirectly via the outlet line. Similarly, the recirculation line can be connected to the gas inlet directly or indirectly via the inlet line. The indirect connection of the recirculation line can be made via a T-piece.

[0024] Recirculation can be achieved passively and / or actively. In passive recirculation, the gas flow supplied to the gas inlet via the inlet line is used as the driving force. To achieve passive recirculation, it is recommended that the gas inlet or inlet line have a cross-sectional constriction similar to a Venturi nozzle, in the area of ​​which the recirculation line opens. This cross-sectional constriction creates a negative pressure that draws the recirculated gas out of the recirculation line.

[0025] Furthermore, it is proposed that a hydrogen filter be integrated into the recirculation line. This reduces the hydrogen content in the recirculated stream, so that less fresh gas or fresh air needs to be introduced to ventilate the volume. The hydrogen filter can be designed, for example, as a palladium membrane or as a recombination catalyst with a downstream gas dryer. The design as a recombination catalyst with a downstream gas dryer offers the advantage that, on the one hand, hydrogen is converted into water, and, on the other hand, the resulting water can be relatively easily removed from the system via gas drying. The gas dryer can be designed as a cold trap to promote condensation or as a silicate dryer, with drying in the silicate dryer occurring through adsorption.This process involves reacting not only the hydrogen contained in the recirculation, but also the oxygen it contains, so that both are removed from the recirculation. This is particularly advantageous when an inert gas is supplied to the volume via the inlet line instead of fresh air in order to inertize the atmosphere. If air or oxygen nevertheless enters the volume to be ventilated, the introduction of air or oxygen into the volume of the enclosure can be compensated for with the help of the recombination catalyst with a downstream gas dryer. The inert atmosphere inside the enclosure allows for higher proportions of hydrogen. This increases safety. Furthermore, active recirculation can reduce the required fan power and the effort required for air treatment (temperature and particle content).

[0026] Advantageously, a heat exchanger is integrated into the recirculation line. With the help of the heat exchanger, the recirculated material can be cooled before it is introduced into the volume. In this way, effective cooling can be achieved simultaneously with the ventilation. Furthermore, it is proposed that the heat exchanger be thermally coupled to another heat exchanger integrated into the inlet line. Using the heat from the recirculated material, the gas or gas mixture in the inlet line can then be tempered, in particular heated, before it is introduced into the volume.

[0027] Preferably, a blower is integrated into the recirculation line. The blower allows for active control of recirculation. Furthermore, unlike passive recirculation, recirculation can be operated independently of the introduction of fresh gas or fresh air. The blower is preferably located downstream of the hydrogen filter and / or the heat exchanger. This allows recirculated material to flow through the blower, which contains little or no hydrogen. The proposed arrangement of the blower thus increases safety.

[0028] In a further development of the invention, it is proposed that at least one cooling unit be arranged on the outside of the housing. The cooling unit provides additional cooling of the gas-filled volume inside the housing. The gas or gas mixture discharged from the volume is therefore less warm. Accordingly, the effort required to cool the gas or gas mixture returned to the volume via the recirculation line is reduced. At high ambient temperatures at the installation site of the stack arrangement, excessive heating inside the housing can also be counteracted. The design with at least one externally arranged cooling element is therefore particularly suitable for hot climates.

[0029] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a first stack arrangement according to the invention, Fig. 2 a schematic representation of a second stack arrangement according to the invention, Fig. 3 a schematic representation of a third stack arrangement according to the invention, Fig. 4 a schematic representation of a fourth stack arrangement according to the invention, Fig. 5 a) and b) each show a schematic representation of a hydrogen filter for a stack arrangement according to the invention, Fig. 6 a first preferred sequence of a method according to the invention and Fig. 7 shows a second preferred sequence of a method according to the invention. Detailed description of the drawings

[0030] The Fig. 1 shows a stack arrangement 1 with a stack 2 and a housing 3. The housing 3 encloses a volume 4 in which the stack 2, including media lines 17 for the required media connection of the stack 2, is accommodated. The stack 2 is an example of one or more stacks 2, whereby the stack 2 or stacks 2 can in particular be an electrolysis stack for the production of hydrogen. The volume 4 accommodating the at least one stack 2 is filled with gas, for example with air. Due to leaks, hydrogen can enter the volume 4, which can then, together with the air present there, form an explosive gas mixture. For safety reasons, the volume 4 must therefore be ventilated. For this purpose, the housing 3 has a gas inlet 5 connected to an inlet line 6 and a gas outlet 7 connected to an outlet line 8, so that ventilation can be carried out via this.Ventilation can not only facilitate gas exchange but also cooling, provided the gas introduced into volume 4 is colder than the gas or gas mixture in volume 4. If necessary, the fresh gas or fresh air must be cooled beforehand.

[0031] The Fig. The stack arrangement 1 shown in Figure 1 further comprises a recirculation line 9, which connects the outlet line 8 to the gas inlet 5. The recirculation line 9 is connected at the other end—parallel to the inlet line 6—to the gas inlet 5. A valve 10 is integrated into the recirculation line 9. When this valve is opened, the gas or gas mixture discharged from the volume 4 via the gas outlet 7 can be recirculated.

[0032] Furthermore, a hydrogen filter 11 is integrated into the recirculation line 9, which removes hydrogen from the gas or gas mixture or reduces the hydrogen content before it is reintroduced into the volume 4. Ventilation can thus be achieved solely with the aid of the recirculated material, so that additional fresh gas or fresh air only needs to be supplied via the inlet line 6 when the hydrogen load is high.

[0033] Furthermore, a heat exchanger 12 is integrated into the recirculation line 9. With the help of the heat exchanger 12, the recirculated fluid can be cooled before it is fed back into volume 4. Thus, effective cooling can be achieved simultaneously with the help of the recirculated fluid.

[0034] A modification of the stack arrangement 1 of the Fig. 1 is in the Fig. 2. It differs from that of the Fig. 1 by an additional fan 14, which is integrated into the recirculation line 9 downstream of the hydrogen filter 11 and the heat exchanger 12. With the help of the fan 14, the recirculation via the recirculation line 9 can be actively controlled if necessary. Furthermore, Fig. 2, the recirculation line 9 is not connected directly to the gas inlet 5, but indirectly via the inlet line 6. The connection can be made, for example, via a T-piece. To save electricity costs, the fan 14 can remain switched off and recirculation can be achieved passively using the gas flow in the inlet line 6.

[0035] A further modification of the stack arrangement 1 of the Fig. 1 shows the Fig. 3. Here, the heat exchanger 12 integrated into the recirculation line 9 is thermally coupled to another heat exchanger 13, which is integrated into the inlet line 6. Through the thermal coupling of the two heat exchangers 12, 13, the heat of the recirculation can be used to heat the fresh gas or fresh air, which is introduced into the volume 4 via the inlet line 6. At the same time, the recirculation is cooled. The stack arrangement 1 of the Fig. 3 further comprises a gas concentration sensor 16 integrated into the outlet line 8, which is in particular a hydrogen sensor, so that the hydrogen concentration in the discharged gas or gas mixture can be measured. In this case, the introduction of fresh gas or fresh air as well as recirculated gas into the volume 4 can be carried out as needed, specifically depending on the measured hydrogen concentration in the discharged gas or gas mixture.

[0036] A further preferred embodiment of a stack arrangement 1 according to the invention is the Fig. 4. In this embodiment, a fan 14 is also provided for active recirculation. However, this fan is arranged upstream of the hydrogen filter 11 and the heat exchanger 12 in the recirculation line 9. Furthermore, the stack arrangement 1 has cooling elements 15 arranged on the outside of the housing 3. With the help of the cooling elements 15, further cooling can be achieved, which prevents the arrangement from overheating. This is particularly advantageous if the stack arrangement 1 is to be used in a hot climate.

[0037] The Fig. 5a) and Fig. 5b) shows examples of a hydrogen filter 11. In the Fig. 5a), the hydrogen filter 11 is designed as a palladium membrane. Fig. 5b) A recombination catalyst 11.1 with a downstream gas dryer 11.2 forms the hydrogen filter 11. Furthermore, gas concentration sensors 16 are integrated into the recirculation line 9 to monitor the filter function and measure the hydrogen concentration in the recirculated product. Instead of measuring with gas concentration sensors, it is possible to determine the gas concentration from the temperature at and / or temperature changes across the recombination catalyst and / or from the amount of condensed water (during cooling) or from the weight gain in a silicate dryer.

[0038] Regardless of the specific design of the stack arrangement 1, the volume 4 enclosed by the housing 3 can also be filled with an inert gas or at least partially with an inert gas instead of with air. The ventilation of the volume 4 is then achieved with the aid of inert gas, which is introduced into the volume 4 via the inlet line 6 and the gas inlet 5. The inert gas can be nitrogen in particular. The inert atmosphere inside the housing 3 allows a higher concentration of hydrogen, so that the gas turnover can be reduced. This means that constant ventilation is not necessary, or the ventilation time and / or the amount of gas introduced for ventilation can be reduced without incurring an increased safety risk.

[0039] The Fig. Figure 6 shows an example of a flow chart for controlling aeration using fresh air and / or recirculated air. This control follows a multi-stage process. In step S1, it is first ensured that a suitable operating state for recirculation exists. This means, for example, that no change in the operating state is imminent and / or that an operating state with a low expected leakage exists. Otherwise, recirculation should preferably not be carried out. If there is no change in the operating state or a defined operating state exists (“+”), a suitable sensor is used in step S2 to check whether the hydrogen concentration and / or the temperature and / or the pressure in volume 4 is within a previously defined non-critical range. If this is the case (“+”), the valve 10 integrated in the recirculation line 9 is opened in step S3 and gas or gas discharged from volume 4 is released.Gas mixture is recirculated passively and / or actively with the aid of the blower 14. In step S4, the hydrogen content in the recirculate is determined, for example based on the temperature development in the recombination catalyst 11.1 and / or based on the amount of water that is subsequently separated from the gas stream in the gas dryer 11.2. If the hydrogen content is low or is within the expected range, aeration can be effected using the recirculate alone in step S5. If the hydrogen content requires increased gas exchange, fresh air can be introduced into volume 4 in addition to the recirculate in step S6. In step S7, the recirculation is stopped or the valve 10 in the recirculation line 9 is closed if the test in step S1 has shown that a change in the operating state is pending ora defined operating state exists ("-") or the test in step S2 has shown that the hydrogen concentration and / or temperature and / or pressure in volume 4 has reached a critical range ("-"). The same applies if the determination of the hydrogen content in step S4 shows that the recirculated product contains too much hydrogen - in particular, more than expected. In this case(s), ventilation is achieved solely with fresh air to achieve maximum gas exchange.

[0040] If nitrogen is introduced into volume 4, this can be determined using the Fig.7 can be applied. Initiation in step 10 initially occurs according to a volume and / or pressure specification. In step S11, the hydrogen concentration in volume 4 of the enclosure 3 increases during operation of the stack arrangement due to leaks. In step S12, the valve 10 integrated into the recirculation line 9 is therefore opened in a time-controlled manner and / or depending on the hydrogen concentration in volume 4, and the gas or gas mixture discharged from volume 4 is recirculated. If recirculation is actively effected, the blower 14 must be switched on. In step 13, the hydrogen content in the recirculate is determined. Here, the procedure can be as in step S4 of the previously described method. The further procedure then depends on the hydrogen content. If a specified limit is undershot, the recirculation can be stopped in step S14 by closing the valve 10 and, if necessary, by switching off the blower 14.If the hydrogen content remains within a lower and an upper limit, recirculation can be continued in step S15. If the upper limit is exceeded, fresh nitrogen can be introduced into volume 4 in step S16. The gas or gas mixture discharged from volume 4 is then discharged via outlet line 8.

Claims

[1] Method for operating a stack arrangement comprising at least one stack (2) and a housing (3) accommodating the at least one stack (2), wherein the housing (3) encloses a gas-filled volume (4) which is connected for gas exchange via a gas inlet (5) to an inlet line (6) and via a gas outlet (7) to an outlet line (8), characterized by that by opening a valve (10) integrated into a recirculation line (9), a gas or gas mixture is discharged from the volume (4) and reintroduced into the volume (4) via the recirculation line (9) and the gas inlet (5). [2] Method according to claim 1, characterized by that the recirculation of the gas or gas mixture is effected passively by means of a gas flow which is introduced into the volume (4) via the inlet line (6) and the gas inlet (5) and / or actively by means of a blower (14) integrated into the recirculation line (9). [3] Method according to claim 1 or 2, characterized by that the recirculated gas or gas mixture is passed through a hydrogen filter (11) before being reintroduced into the volume (4). [4] Method according to one of the preceding claims, characterized by that the recirculated gas or gas mixture is tempered, preferably cooled, before being reintroduced. [5] Method according to one of the preceding claims, characterized by that the valve (10) integrated into the recirculation line (9) is opened in a time-controlled manner and / or depending on the gas composition in the volume (4) and / or depending on the gas composition of the recirculate. [6] Method according to one of the preceding claims, characterized by that an inert gas, preferably nitrogen, is introduced into the volume (4) via the inlet line (6). [7] Stack arrangement (1) for an electrochemical system, in particular an electrolysis system or a fuel cell system, comprising at least one stack (2) and a housing (3) accommodating the at least one stack (2), wherein the housing (3) encloses a volume (4) which is connected to an inlet line (6) via a gas inlet (5) and to an outlet line (8) via a gas outlet (7), and wherein a connection of the gas outlet (7) or the outlet line (8) to the gas inlet (5) or the inlet line (6) can be established via a recirculation line (9) with an integrated valve (10). [8] Stack arrangement (1) according to claim 7, characterized by that the gas inlet (5) or the inlet line (6) has a cross-sectional constriction in the manner of a Venturi nozzle, in the area of ​​which the recirculation line (9) opens. [9] Stack arrangement (1) according to claim 7 or 8, characterized bythat a hydrogen filter (11) is integrated into the recirculation line (9), wherein the hydrogen filter (11) is preferably designed as a palladium membrane or as a recombination catalyst (11.1) with a downstream gas dryer (11.2). [10] Stack arrangement (1) according to one of the preceding claims, characterized by that a heat exchanger (12) is integrated into the recirculation line (9), which is preferably thermally coupled to a further heat exchanger (13) which is integrated into the inlet line (6). [11] Stack arrangement (1) according to one of the preceding claims, characterized by that a blower (14) is integrated into the recirculation line (9), which is preferably arranged downstream of the hydrogen filter (11) and / or the heat exchanger (12). [12] Stack arrangement (1) according to one of the preceding claims, characterized by that at least one cooling unit (15) is arranged on the outside of the housing (3).

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