EP4339327A1 - Method for operating an electrolysis system, and electrolysis system - Google Patents

Abstract

The invention relates to a method for operating an electrolysis system (100), in which a liquid medium is converted into at least one gaseous product in an electrolysis unit (110), with a container (120) used as a gas separator and the electrolysis unit (110) a fluid stream (b, c) is circulated, which has liquid medium and at least temporarily gas, the fluid stream (b, c) being guided through at least one axial cyclone (140) in order to separate gas from the liquid medium in the fluid stream, wherein the separated gas (g) is removed from the fluid stream (b, c). The invention also relates to a corresponding electrolysis system (100) and to the use and production of an axial cyclone (140).

Description

The invention relates to a method for operating an electrolysis system, in particular for water electrolysis, such an electrolysis system, which is used, for example, to obtain hydrogen, and a use and a method for producing an axial cyclone.

State of the art

To obtain hydrogen, so-called electrolysis can be used, in which, for example, water is split or converted into oxygen and hydrogen using electrical energy. This is also referred to as water electrolysis. Here, for example, the so-called proton exchange membrane electrolysis (PEM electrolysis, “proton exchange membrane” electrolysis) comes into consideration.

When water is electrolyzed, the temperature of the water usually rises. To limit the temperature rise, large amounts of water can be recirculated. In this case, a large part of the water usually remains on the oxygen side of the membrane during PEM electrolysis. For example, while the hydrogen diffuses through the membrane, the oxygen initially remains in the water and is then typically separated from the water in a container, at least that proportion of oxygen that exceeds the solubility limit in water under given conditions. The container is therefore used as a gas separator or in this case in particular as an oxygen separator or oxygen-water separator.

However, oxygen or oxygen bubbles need a certain amount of time to rise to the surface in the water and be considered separated; The exact time can depend on the flow direction and size of the container, for example. However, the longer the water (with any oxygen dissolved in it) stays in the container, the larger it has to be in order to be able to circulate the necessary amount of PEM or the electrolysis unit. This can lead to high costs. This basically also applies to other types of electrolysis, in which a gas is circulated in liquid Medium remains. Remaining oxygen in the water can have a negative effect on electrolysis. Against this background, the task is to improve the separation of gas such as oxygen from a liquid such as water.

Disclosure of the invention

This object is achieved by a method for operating an electrolysis system, an electrolysis system and a use and a method for producing an axial cyclone with the features of the independent patent claims. Refinements are the subject of the dependent patent claims and the following description.

Advantages of the invention

The invention deals with electrolysis and electrolysis systems and their operation. Electrolysis systems are typically used to produce or obtain hydrogen using electrolysis. Here we are talking about the so-called water electrolysis, in which water is converted (split) into hydrogen and oxygen (in addition to hydrogen, oxygen is also always obtained or produced). When it comes to water electrolysis, there is, for example, the so-called alkaline water electrolysis (AEL, "Alkaline Electrolysis") or the so-called proton exchange membrane electrolysis (PEM electrolysis, "Proton Exchange Membrane" electrolysis). The basics for this are known, for example from " Bessarabov et al: PEM electrolysis for hydrogen production. CRC Press ."

There is also the so-called solid oxide electrolyzer cell electrolysis (SOEC electrolysis, "Solid Oxide Electrolysis Cell" electrolysis) and the anion exchange membrane electrolysis (AEM electrolysis, "Anion Exchange Membrane" electrolysis). In particular, those electrolysis technologies that take place at low temperatures, such as PEM, AEL and AEM electrolysis, are suitable for supporting the transition of energy production to renewable energies due to the possibilities of flexible operation.

Solid oxide electrolyzer cell electrolysis is also suitable, for example, for obtaining carbon monoxide from carbon dioxide, i.e. for carbon dioxide electrolysis (CO ₂ electrolysis); There is also the so-called co-electrolysis, in which carbon dioxide and water are converted into various products such as CO, synthesis gas or ethylene, ethanol, formate. There is also the so-called chlorine-alkali electrolysis.

In PEM electrolysis, for example, water, and in particular demineralized water, is fed as the feed medium to an electrolysis unit with a proton exchange membrane (PEM), in which the feed medium, i.e. the water, is converted (split) into hydrogen and oxygen.

PEM electrolysis of water usually results in an increase in the temperature of the water. To limit the temperature rise, large amounts of water can be recirculated. In this case, a large part of the water in PEM electrolysis usually remains on the oxygen side of the membrane or the oxygen side of the electrolysis unit. While the hydrogen, for example, diffuses through the membrane, the oxygen initially remains in the water and is then typically separated from the water in a container, at least the proportion of oxygen that exceeds the (maximum) solubility in water.

However, oxygen or oxygen bubbles need a certain amount of time to rise to the surface due to the density difference in the water and be considered separated; The exact time can depend, for example, on the size of the bubble, the direction of flow and the size of the container. However, the longer the water stays in the container, the larger it has to be in order to be able to circulate the necessary amount of PEM. This can lead to high costs. If the time spent in the container is kept too short, oxygen can remain in the water. In particular, small oxygen bubbles can have a negative impact on electrolysis, particularly with regard to the performance, efficiency and service life of the electrolysis system or electrolysis unit.

Against this background, the use of one or possibly several axial cyclones in an electrolysis system is proposed, in particular so-called inline axial cyclones, ie axial cyclones that are installed or arranged in lines or pipes. An axial cyclone has a so-called guide element (also referred to as a “swirl element”) that lies in a fluid stream. With the guide element, a twist is imposed on the fluid, which leads to the heavier phase of the fluid flow being at the edge of the Axial cyclone or the line collects, while the lighter phase lies in the middle, i.e. in the core flow. Both phases can then - at least to a certain extent - be subtracted separately from each other.

A typical use of such axial cyclones is actually in undersea applications, for example in oil production. There the petroleum is separated from water so that the petroleum can be extracted. However, the inventors have now recognized that such an axial cyclone can also be used particularly well to separate a gas such as oxygen from a liquid such as water.

As mentioned, an electrolysis system circulates water with possibly oxygen in it; This takes place between the electrolysis unit with, for example, the PEM and the container in which, for example, the oxygen is separated from the water. Accordingly, several fluid lines are provided between the container and the electrolysis unit, on the one hand in the flow direction from the container to the electrolysis unit and on the other hand in the flow direction from the electrolysis unit to the container. One or more fluid lines can be provided in each direction, depending on the size or diameter of the fluid lines and the size of the electrolysis system. In an electrolysis system with an output of 24 MW, for example, one or two fluid lines, for example in the form of pipes, with a diameter of, for example, 700 mm per flow direction can be used.

An axial cyclone is now arranged or used in such a way that a fluid stream with water and at least temporarily oxygen is guided through the axial cyclone. For this purpose, the axial cyclone can be arranged in one of the fluid lines mentioned. If there are several fluid lines in one flow direction, an axial cyclone can also be arranged in each fluid line. The fluid lines or pipes, which are generally necessary anyway, are particularly suitable for the use of axial cyclones.

The oxygen collects after the axial cyclone (in the direction of flow) in the middle of the pipe or centrally and can then be removed from there, e.g. through a thin pipe inserted there that is led to the outside.

Due to the high accelerations of up to 100 g in the radial direction It doesn't matter whether the axial cyclone is arranged vertically or horizontally. The axial cyclones can be operated at speeds from, for example, approx. 2 m/s (and higher), which fits very well with the typical speeds in a typical electrolysis plant on the oxygen side.

It is particularly useful if such an axial cyclone (or possibly several) are used in the flow direction between the electrolysis unit and the container. This means that a significant amount of oxygen is already separated from the fluid stream or the water before it reaches the container that is actually used for oxygen separation. Accordingly, both this container and the lines between the axial cyclone and the separator (container) can then be made significantly smaller or more compact than without the use of the axial cyclone. A more compact design also allows easier or better standardization of such containers, e.g. in a skid design of the oxygen-water separator.

In addition to the coarse separation of oxygen, the use of such an axial cyclone (or possibly several) enables the coalescence and/or separation of tiny bubbles. In this case too, the subsequent separator can be made smaller or more compact than without the use of the axial cyclone. In addition, installations in the separator can be saved if necessary.

An additional separation of oxygen from the water using ultrasound is also useful. Ultrasound treatment removes small floating gas bubbles from the liquid and reduces the dissolved gas content to the natural equilibrium value. An even higher degree of separation can be achieved through a combination of axial cyclone(s), containers and ultrasound. The ultrasound can be used, for example, between the electrolysis unit and the container as well as in the container itself.

Although the electrolysis or electrolysis is described in relation to the water electrolysis or in particular the PEM electrolysis, the axial cyclones mentioned can also be used in other electrolysis systems such as those mentioned above, in which a liquid medium in the electrolysis unit in at least one gaseous product is implemented, and accordingly between A fluid stream is circulated in the container and the electrolysis unit, which has liquid medium and at least temporarily gas. The mode of operation of the axial cyclone is not limited to oxygen and water, but generally extends to two mixed media that have different densities, and therefore in particular to a mixture of liquid (liquid medium) and gas.

The axial cyclones used in the electrolysis system may need to be adapted to the existing sizes or diameters of fluid lines or pipes in the electrolysis system. In this respect, it is particularly useful if the shape and/or material of an axial cyclone is specifically adapted to its use there. This can be done particularly easily and well if the axial cyclone or at least its guide element is manufactured using additive manufacturing, also known as 3D printing.

The invention will be explained in more detail below with reference to the accompanying drawing, which shows a system according to a preferred embodiment of the present invention.

Figur 1

zeigt schematisch eine erfindungsgemäßen Elektrolyseanlage in einer bevorzugten Ausführungsform.

Figur 2

zeigt schematisch einen Axialzyklon in einer Rohrleitung.

Short description of the drawing

Figure 1

shows schematically an electrolysis system according to the invention in a preferred embodiment.

Figure 2

shows schematically an axial cyclone in a pipeline.

Detailed description of the drawing

In Figure 1 an electrolysis system 100 according to the invention is shown schematically in a preferred embodiment, in which a method according to the invention can also be carried out. An example is an electrolysis system for water electrolysis using PEM. In particular, the electrolysis system shown here and generally described within the scope of the invention is an electrolysis system on an industrial scale, for example to produce hydrogen on an industrial scale. A typical output of such an electrolysis system is, for example, more than 10 MW or even more than 20 MW.

The electrolysis system 100 has an electrolysis unit 110, or a so-called electrolysis cell, in which a proton exchange membrane (PEM) 112 is provided. The PEM 112 separates the electrolysis unit 110 into an oxygen side 114 and a hydrogen side 116.

The electrolysis system 100 also has a container 120, which serves as a gas separator, here in particular as an oxygen separator or oxygen-water separator. The container 120 is connected to the electrolysis unit 110 via one or more fluid lines 122, e.g. pipes. Through the one or more fluid lines 122, a fluid stream b can be pumped from the container 120 to the electrolysis unit, for example by means of a pump 124. The electrolysis unit 110 is also connected to the container 120 via one or more fluid lines 126, for example pipes. A fluid stream c can be pumped from the electrolysis unit 110, there the oxygen side 114, to the container 120 through the one or more fluid lines 126; The pump 124 is also sufficient for this.

In addition, the electrolysis system 100 has a further gas separator 130, here a hydrogen separator or hydrogen-water separator.

Although only one electrolysis unit 110 is shown here, several of them can also be provided, for example depending on the size and performance of the electrolysis system 100. Several electrolysis units can then, for example, still be connected to a common container for gas or oxygen separation and/or a common one Hydrogen separator must be connected.

When the electrolysis system 100 is in operation, the fluid stream b, which contains water, is pumped from the container 120 to the electrolysis unit 110. There the water is converted into oxygen and hydrogen. For this purpose, an electrical voltage is applied to the electrolysis unit 110, the hydrogen diffuses through the PEM 112 to the hydrogen side 116 and from there, possibly mixed with water vapor, can be fed to the hydrogen separator 130 as current e. The hydrogen can be separated there and discharged or stored as electricity f, for example for further use.

The oxygen remains together with the water on the oxygen side 114 and, as mentioned, is pumped to the container 120 as a fluid stream c. Overall, a fluid stream is circulated between the container 120 and the electrolysis unit 110. The fluid flow or partial fluid flow c has more oxygen than the fluid flow or partial fluid flow b, since the fluid flow c includes the oxygen generated in the electrolysis unit 110. In the fluid stream b, however, oxygen has already been separated at least in the container 120.

As mentioned, oxygen is separated from water in container 120; The oxygen separated or deposited here can be discharged or stored as stream d, for example for further use.

Since water is converted into oxygen and hydrogen in the electrolysis unit 110 and the oxygen and hydrogen are removed, the amount of water becomes smaller and can therefore - in order to maintain continuous operation - be used as a stream of externally new water (so-called make-up -water).

This water a can, for example, be prepared beforehand, but this is no longer relevant to the present invention. Likewise, if necessary, water separated in the hydrogen separator 130 can be fed back into the container 120, if necessary also after previous processing.

Furthermore, the electrolysis system 100 has, for example, an axial cyclone 140, which is only indicated schematically here. The axial cyclone 140 is arranged in the fluid line 126 and thus in the flow direction between the electrolysis unit 110 and the container 120. It is conceivable to arrange an axial cyclone - alternatively or additionally - in the direction of flow between the container 120 and the electrolysis unit 110, as shown for example at 140 '.

As mentioned, the axial cyclone serves here to separate oxygen from the water in the fluid stream. Separated oxygen can be discharged as a stream g, for example for further use and, if necessary, stored. The stream g can also be combined with the stream d or fed to the separator 120.

In Figure 2 is a schematic of the axial cyclone 140 Figure 1 presented in more detail. The axial cyclone 140 is arranged in the fluid line 126 and has a guide element comprising a base body 142 and guide vanes 144 which are arranged or formed on the base body 144.

The fluid flow c, comprising water h and oxygen i, comes from the right and hits the axial cyclone 140 or its guide element. In front of the axial cyclone 140, the oxygen i, shown here as thick dots, is mixed with the water h, shown here as fine or small dots. Due to the flow speed of the fluid stream c, a swirl is generated in the fluid stream by the axial cyclone 140, which causes the water h to collect as a heavy phase at the edge of the fluid line 126, while the oxygen i as a light phase collects in the middle or in the middle Center of the flow. This is indicated to the left of the axial cyclone 140 by thick dots that are getting closer and closer together, which are finally only shown as a thick line in the middle - there is then only oxygen there.

Furthermore, a line 150 is introduced into the fluid line 126, which has an opening which lies in the middle of the fluid line 126 and is at a suitable distance from the axial cyclone 140. The line 150 is then, for example, guided to the outside, for example through a wall or in the fluid line 126 (here, for example, a suitable seal must be made). Because the oxygen collects in the middle of the fluid line 126, it passes through the opening of the line 150 due to the flow velocity and can be discharged as flow g, if necessary via a valve 152, as already mentioned.

Downstream, the fluid flow c then has less oxygen than before. As an example, no oxygen in a gaseous state is shown in the water anymore. In this way, the fluid stream c, when it then reaches the container 120, contains significantly less oxygen than without the use of the axial cyclone.

Claims (12)

Method for operating an electrolysis system (100), in which a liquid medium is converted into at least one gaseous product in an electrolysis unit (110), wherein a fluid stream (b, c) which contains liquid medium and at least temporarily gas is circulated between a container (120) used as a gas separator and the electrolysis unit (110), wherein the fluid stream (b, c) is passed through at least one axial cyclone (140) in order to separate gas from the liquid medium in the fluid stream, the separated gas (g) being removed from the fluid stream (b, c). Method according to claim 1, wherein the fluid stream (c), in the direction of flow, is guided through an axial cyclone (140) between the electrolysis unit (110) and the container (120). A method according to claim 1 or 2, wherein gas is further separated from the liquid medium in the fluid stream by means of ultrasound. Method according to one of the preceding claims, wherein in the electrolysis unit (110) water as a liquid medium is converted into hydrogen and oxygen as gaseous products, and wherein the fluid stream (b, c) has water and at least temporarily oxygen as gas. The method according to claim 4, wherein the electrolysis unit (110) has a proton exchange membrane on which the water is converted into hydrogen and oxygen. Electrolysis system (100) with an electrolysis unit (110), in which a liquid medium can be converted into at least one gaseous product, with a container (120) to be used as a gas separator, and with several fluid lines (122, 126) via which the Container (120) and the electrolysis unit (110) are connected, wherein the electrolysis system (100) is set up to circulate a fluid stream (b, c) through the plurality of fluid lines (122, 126) between the container (120) and the electrolysis unit (110), the fluid stream (b,) being liquid medium and at least has gas at times, wherein the electrolysis system (100) has at least one axial cyclone (140) for separating gas from the liquid medium in the fluid stream, wherein the at least one axial cyclone (140) is arranged in at least one of the plurality of fluid lines (122, 126), and wherein the electrolysis system (100) is set up to remove the gas (g) separated from the fluid stream (b, c) by means of the at least one axial cyclone (140). Electrolysis system (100) according to claim 6, wherein an axial cyclone (140) is arranged in a fluid line (126) arranged in the flow direction between the electrolysis unit (110) and the container (120). Electrolysis system (100) according to claim 6 or 7, which is further adapted to separate gas from the liquid medium in the fluid stream using ultrasound. Electrolysis plant (100) according to one of claims 6 to 8, which is set up for water electrolysis, wherein in the electrolysis unit (110) water as a liquid medium can be converted into hydrogen and oxygen as gaseous products, and wherein the fluid stream (b, c) is water and at least temporarily has oxygen as a gas. Electrolysis system (100) according to claim 9, wherein the electrolysis unit (110) has a proton exchange membrane on which the water can be converted into hydrogen and oxygen. Use of an axial cyclone (140) in an electrolysis system (100), in particular according to one of claims 6 to 10, for separating gas (g) from a liquid medium in a fluid stream (c) in the electrolysis system (100). Method for producing an axial cyclone (140) for use in an electrolysis system (100), in particular according to one of claims 6 to 10, wherein at least one guide element (142, 144) of the axial cyclone (140) is produced by means of additive manufacturing.

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