EP4123057A1 - Optimised liquid discharge from membrane electrolyzers - Google Patents

Abstract

A method for operating an electrolysis device with a plurality of electrolyzers selected from membrane electrolyzers is described, with at least each electrolyzer having at least one liquid outlet and at least one gas outlet on the anode side, and separately on the cathode side at least one liquid outlet and at least one gas outlet and the anode chambers of these electrolyzers one below the other as well as separately from this, the cathode chambers of these electrolysers are connected to one another at least via a liquid supply (2.2), a gas discharge (2.4) and a liquid discharge (2.5), characterized in that the operating pressure of at least one liquid discharge (2.5) is set lower than the operating pressure of the electrolysers will and therea. the liquid drains from the anode compartments or the cathode compartments or from both of these compartments of the electrolysers via a pipe siphon (2.14) into the pipe system of the liquid discharge (2.5), whereby with each pipe siphon (2.14) on the liquid discharge side the operating pressure of the electrolysers differs from the lower operating pressure of the subsequent one pipeline system of the liquid discharge (2.5) is decoupled, andb. each gas discharge of the electrolysers decoupled with a pipe siphon (2.14) is carried out individually for each electrolyser via an individual control valve (2.16) for each electrolyser into the common gas discharge (2.4). This method and a suitably configured electrolysis device allow the liquid discharge (2.5) to be controlled by the operating pressure of the Decoupling electrolysers and making it easier to switch from the start-up to the operational piping system.

Description

The invention relates to the provision of electrolysis devices with membrane electrolyzers with an optimized liquid flow, and a method for operating these electrolysis devices.

Electrolysis processes for the production of basic chemicals have to be developed for production on a large industrial scale (several 1000 t/a). Large-area electrolytic cells and electrolyzers with a large number of electrolytic cells are necessary in order to produce industrial quantities of product using electrolysis methods.

As is known from chlor-alkali electrolysis, electrolytic cells with an electrode area of more than 2m ² per electrolytic cell are usually used. The electrolysis cells are combined in groups of up to 100 in an electrolysis frame. Several racks then form an electrolyser. The capacity of an industrial electrolyser, for example for chlorine production, is currently up to 30,000 t/a of chlorine and the respective equivalents of caustic soda or hydrogen.

In the performance of some electrolysis processes, at least one of the electrode half-reactions liberates a gaseous product, such as oxygen and hydrogen in water electrolysis, or chlorine and optionally hydrogen in chlor-alkali electrolysis. This formation of gas often results in a pressure difference between the operating pressure of the electrolyzer and the operating pressure of the liquid discharge line from the electrolyzer. For example, in conventional chlor-alkali membrane electrolysis, the products chlorine, aqueous alkali metal hydroxide solution (lye) and hydrogen are produced by electrolysis of an aqueous alkali metal salt solution. The reaction equation for the production of sodium hydroxide lye is given here as an example:

_{2NaCl +} 2H2O → Cl2 + 2NaOH ₊ H2

The pressure difference described above is also observed when operating electrolysers with gas diffusion electrodes, in which the operating pressure of the electrolyser is at least influenced by the reactant gas introduced or its residual gas removed (e.g. oxygen when operating an oxygen-consuming cathode or, for example, carbon dioxide when operating a CO ₂ electrolysis with Gas diffusion electrode) is optionally influenced in combination with the product gas formed during the electrolysis.

Irrespective of the type of electrode selected, several electrolysis devices (electrolysers) are usually operated in parallel in corresponding electrolysis systems. The electrolyzers include, for example, in DE19641125 described, each in turn several individual electrolytic cells connected hydraulically in parallel, through which electric current flows in an electrical series connection (“bipolar electrolyzers”) or also in an electrical parallel connection (“monopolar electrolyzers”).

The supply of the electrolysers with the operating media (e.g. brine for the anode side, lye for the cathode side) and the removal of the products (e.g. chlorine gas and depleted brine "anolyte" from the anode side and hydrogen and enriched lye "catholyte" from the cathode side) generally take place via operational piping systems that connect the electrolysers to the appropriate treatment plants and to which the electrolysers are connected in parallel. Typical arrangements of electrolysers and piping systems in an electrolysis cell room can, for example Ullmann's Encyclopedia of Industrial Chemistry, Chapter "Chlorins ", to be taken.

The electrolysers are usually operated at elevated temperature and elevated pressure, typical values are approx. 40 - 90 °C and an operating pressure of approximately atmospheric pressure to 200 - 500 mbar overpressure. An operating overpressure in the electrolytic cell offers the advantage that the subsequent processing steps of the gaseous products, such as chlorine and hydrogen (condensation of moisture), run more easily, especially on the anolyte side of the electrolysers, and the subsequent compression has better starting conditions and intermediate compressors that may be required are not required be able. However, the additional measures described below are necessary in order to achieve normal operation at increased pressure/temperature between a depressurized standstill and start-up and shut-down operation.

The operating media are usually fed to the electrolytic cells from below; the products leave the electrolytic cells in overflow. As a result, the electrolytic cells are always filled with liquid when they are switched on or off, or with a liquid/gas mixture during normal operation due to the gases that are produced.

Typical designs of membrane electrolytic cells and electrolysers and common operating data are described, for example, in the Handbook of Chlor-Alkali Technology, Chapter 5 "Chlor-Alkali Technologies".

For commissioning, the electrolysers must be heated up from the ambient conditions (atmospheric pressure, room temperature) to the operating temperature and pressurized to the operating pressure, and for decommissioning they must be cooled down and expanded accordingly. Exemplary procedures for start-up and shut-down are described, for example, in the Handbook of Chlor-Alkali Technology, Chapter 13 "Plant Commissioning and Operation".

A common technical solution for these start-up processes is to connect the electrolysers to start-up circuits via separate start-up piping systems, so that individual electrolysers can be switched on or off independently of the others that are in operation.

A typical start-up process is as follows: An electrolyser is filled with the operating media via the separate start-up circuits. The operating media are then circulated and heated up until the target temperature for operation is reached. Now the circulation is stopped via the start-up circuit. The anode and cathode sides of the electrolyser are pressurized (e.g. by adding nitrogen) to the operating pressures. After the connection to the operational piping systems has been opened and the circulation through these operational piping systems has been restarted, the electric current (hereinafter referred to as electrolysis current) can be switched on and the electrolyzer can thus be put into operation.

A typical decommissioning process runs the other way around, analogously to commissioning: After the electrolysis current has been switched off, the circulation via the operational piping systems is stopped and the electrolyser is separated from these operational piping systems. Anode and cathode spaces are relieved. It should be noted that the differential pressure between the anode and cathode chambers remains within the specified operating parameters. The circulation is restarted via the start-up piping system and the electrolyser is cooled down.

Depending on the details of the technology used (e.g. type of electrode coating), an auxiliary rectifier is switched on when a certain temperature is reached during commissioning low polarization current (order of magnitude: a few 10 A), which protects the electrode coating from damage; when decommissioning, it is switched off again when the temperature falls below a certain level and as soon as the anode chamber has been rinsed free of chlorine. The polarization rectifier can remain switched on during the short interruption of the circulation when switching over from the start-up to the operating circuits during start-up or vice versa during decommissioning. Since the electrolytic cells of conventional design are filled with liquid during these processes, no damage can be caused by the polarization current.

The parameters mentioned above for the general mode of operation of the electrolysers and for the structure of the electrolysis device are to be applied analogously to the water electrolysis. Technical systems for alkaline water electrolysis as well as for polymer electrolyte-based electrolysis, the so-called PEM electrolysis, are known and commercially available. The principles of water electrolysis are exemplified in Chapter 6.3.4 in Volkmar M. Schmidt in "Electrochemical Process Engineering" (2003 Wiley-VCH-Verlag; ISBN 3-527-29958-0 ) described.

In a new development, eg chlor-alkali electrolysis, an additional catalyst arranged on the electrode-side current distributor of the electrolysis cells, usually referred to as a gas diffusion electrode (GDE), is used. If oxygen is used as the educt gas, the gas diffusion electrode is also referred to as an oxygen-depleting cathode (SVK) or oxygen depolarized cathode (ODC). This is used, for example, in chlor-alkali electrolysis, whereby lye (OH ^- ) is produced instead of hydrogen (H ₂ ) in a modified cathode reaction with the addition of oxygen. This altered cathode reaction is associated with a lower electrolysis voltage and corresponding energy savings. The following reaction equation results for the example of the production of sodium hydroxide lye:

_4NaCl + O2 ₊ 2H2O → _2Cl2 + 4NaOH

As an application of a gas diffusion electrode, in addition to chlor-alkali electrolysis, those in the published application are examples DE 102020207186 A Electrolysis of CO ₂ / CO described in DE 102020207186 A described production of CO from CO ₂ with the intermediate step of the electrolytic production of formic acid or in DE 102020207186 A described electrolytic cell with gas diffusion electrode for CO ₂ reduction called.

The use of a gas diffusion electrode is described below as an example for chlor-alkali electrolysis. In it, an oxygen-consuming cathode is used as a gas diffusion electrode. The oxygen supply to the electrolysers, which is necessary to maintain the oxygen consumption reaction, can be carried out by simply flowing through the electrolytic cells, as for example in DE 102013011298 A described or contain an additional recycling step as in DE 10149779 A intended.

In any case, for the integration of this technology into the existing electrolyzer technology, the three-phase reaction between the operating liquid, catalyst and oxygen gas has to be solved as an additional task.

In a currently preferred technical embodiment, this is done in the context of a chlor-alkali electrolysis, as for example in the published application EP 2746429 A described in such a way that the alkali metal hydroxide lye trickles down as a liquid film in front of the catalyst layer and runs out of the bottom of the electrolytic cell, while the oxygen gas is introduced from the back of the catalyst layer.

As a result, the volume of liquid on the cathode side of the electrolytic cell is very small compared to conventional chlor-alkali membrane electrolysis and, since the liquid no longer drains via an overflow, in contrast to conventional electrolysis, but directly through an outlet at the bottom of the electrolytic cell, the If the liquid circulation is interrupted, the liquid content drains out of the cells within a very short time.

A polarization current applied to protect the electrode coating and the catalyst of the oxygen-consuming cathode during startup/shutdown would have to be switched off immediately if the liquid circulation is interrupted, e.g. to avoid short circuits in an electrolytic cell that has run dry on the cathode side.

In newly designed chlor-alkali electrolysis plants that work with oxygen-consuming cathode technology, the electrolysers are connected in parallel to the operating and start-up pipeline systems, analogously to conventional electrolysis technology.

In contrast to conventional electrolysis technology, however, the interruption of the liquid circulation (here on the cathode side) when connecting individual electrolyzers to the operational piping system or separating individual electrolyzers from the operational piping system should be avoided. The disruption of fluid circulation and the the resulting switching off of the polarization current would lead to damage to the oxygen-depleting cathode.

With the usual installations (separation of the systems via manual and process control-controlled valves), this task could only be implemented with great effort, if at all, by automating various previously manually operated valves (some with large nominal diameters up to DN 400) via variable-speed drives and with would have to be provided with a control system which switches the cathode side of the electrolyser from the start-up to the operating piping system without interrupting the liquid circulation and at the same time raises the pressure to the operating pressure. Vice versa when switching off.

It has now been found that the switching process for the electrode side, in particular for the gas diffusion electrode side, of the electrolysers can be significantly simplified if the liquid-side decoupling of the electrolysers from the operating piping system no longer takes place via fittings, but via a liquid-filled siphon and the electrode-side, in particular the gas pressure regulation on the gas diffusion electrode side is no longer carried out centrally for all electrolyzers together, but for each electrolyzer individually.

1. a. die Flüssigkeitsabläufe aus den Anodenräumen oder den Kathodenräumen oder aus beiden dieser Räume der Elektrolyseure je Elektrolyseur über einen Rohrleitungssiphon in das Rohrleitungssystem der Flüssigkeitsabfuhr erfolgt, wodurch mit jedem Rohrleitungssiphon flüssigkeitsablaufseitig der Betriebsdruck der Elektrolyseure vom niedrigeren Betriebsdruck des anschließenden Rohrleitungssystems der Flüssigkeitsabfuhr entkoppelt wird, und
2. b. jede Gasableitung der mit Rohrleitungssiphon entkoppelten Elektrolyseure für jeden Elektrolyseur einzeln über ein individuelles Regelventil pro Elektrolyseur in die gemeinsame Gasabfuhr erfolgt.

One subject of the invention is therefore a method for operating an electrolysis device with a plurality of electrolyzers selected from membrane electrolyzers, with at least each electrolyzer having at least one liquid outlet and at least one gas outlet on the anode side, and separately on the cathode side at least one liquid outlet and at least one gas outlet and the anode chambers of these Electrolysers are connected to each other and separately the cathode chambers of these electrolysers are connected to each other via at least one liquid supply, one gas discharge and one liquid discharge, characterized in that the operating pressure of at least one liquid discharge is set lower than the operating pressure of the electrolysers and

1. a. the liquid drains from the anode spaces or the cathode spaces or from both of these spaces of the electrolysers per electrolyser via a pipeline siphon into the pipeline system of the liquid discharge, whereby the operating pressure of the electrolysers decreases with each pipeline siphon on the liquid discharge side lower operating pressure of the subsequent pipeline system of the liquid discharge is decoupled, and
2. b. each gas discharge of the electrolysers, which are decoupled with a pipeline siphon, is carried out individually for each electrolyser via an individual control valve for each electrolyser into the common gas discharge.

The electrolysers of said electrolysis device can be operated with conventional electrodes. It is important that during operation the operating pressure of at least one liquid discharge is set lower than the operating pressure of the electrolysers. It has been found to be particularly suitable according to the invention if the electrolysis device operated by the method is operated on the anode side and/or cathode side with gas diffusion electrodes and a gas supply provided for this purpose. For this purpose, the operated electrolysis device contains several electrolyzers selected from membrane electrolyzers with gas diffusion electrodes, in particular with oxygen-consuming cathodes, these electrolyzers at least having a gas supply on the gas diffusion electrode side, a liquid supply on the gas diffusion electrode side as liquid supply, a residual gas discharge on the gas diffusion electrode as gas discharge and a liquid discharge on the gas diffusion electrode side are connected to each other as a liquid drain.

In a preferred embodiment of the method, the electrolyzers are selected from alkali metal chloride membrane electrolyzers with an oxygen-consuming cathode as the gas diffusion electrode. A suitable alkali metal chloride that can be used for this embodiment is, for example, at least one alkali metal chloride selected from lithium chloride, sodium chloride and potassium chloride, sodium chloride being preferred.

Through the pipeline siphon, the liquid circulation on the electrode side, preferably the gas diffusion electrode side, can continue to be operated continuously when an electrolyzer is started up, while the gas pressure on the electrode side, preferably the gas diffusion electrode side, is adjusted to the operating value via the pressure control.

The liquid level in the leg of the pipeline siphon facing the electrolyte outlet of the electrolyser adjusts itself automatically to the changed operating pressure of the electrolyser if the drain side of the siphon drains into a piping system with a lower operating pressure.

In one embodiment of the method according to the invention, it has proven to be advantageous if the operating pressure on the electrode side, preferably the gas diffusion electrode side, of the electrolyzer is between atmospheric pressure and 1 bar overpressure, preferably in a range from 100 to 500 mbar overpressure.

According to the invention, the reference pressure for specifying an overpressure is, unless explicitly defined otherwise, the atmospheric pressure.

According to the invention, the operating pressure on the electrode side, preferably the gas diffusion electrode side, is the gas pressure in the gas space of the electrolytic cells on the electrode side, preferably on the gas diffusion electrode side.

1. (i) das Gas, ausgewählt aus Produktgas, Restgas, Gemisch aus Produktgas und Restgas und
2. (ii) die Flüssigkeit

zunächst gemeinsam als Gemisch in einer Ablauf-Sammelleitung jedes einzelnen Elektrolyseurs aus dem Elektrolyseur heraus geführt werden und anschließend dieses Gemisch einer Gas-Flüssigkeits-Trennung unterzogen wird, wobei nach erfolgter Trennung das Gas über die Gasableitung gemäß Schritt b. und die Flüssigkeit über den Flüssigkeitsablauf gemäß Schritt a. bewirkt wird. Dabei hat es sich als bevorzugt geeignet herausgestellt, dass bei Einsatz einer Gasdiffusionselektrode, besagte Ablauf-Sammelleitung des Elektrolyseurs Gasdiffusionselektroden-seitig betrieben wird.It is preferred according to the invention if

1. (i) the gas selected from product gas, tail gas, mixture of product gas and tail gas and
2. (ii) the liquid

are first led out together as a mixture in an outflow manifold of each individual electrolyzer out of the electrolyzer and this mixture is then subjected to a gas-liquid separation, with the gas being discharged via the gas discharge line according to step b. and the liquid via the liquid outlet according to step a. is effected. It has turned out to be particularly suitable that when using a gas diffusion electrode, said drain manifold of the electrolyzer is operated on the gas diffusion electrode side.

Within the framework of a preferred embodiment of the gas-liquid separation of the process, gas and liquid are separated by their density difference in a pipeline which is connected to the discharge collecting line and is preferably routed vertically with a tolerance of ±15° and is discharged separately. The gas flows upwards in the direction of the pressure control associated with each electrolyser; the liquid drains down into the pipeline siphon.

In a further embodiment of the method according to the invention, it is advantageous if the operating pressure on the outlet side of the pipeline siphon is lower than the operating pressure on the inlet side of this pipeline siphon, preferably between atmospheric pressure and 100 mbar overpressure.

According to the invention, the operating pressure on the outlet side of the pipeline siphon is the gas pressure in the gas space of the system parts following the outlet side of the siphon.

According to the invention, the operating pressure on the inlet side of the pipeline siphon is the gas pressure in the outlet manifold of the electrolyzer, which is connected on the one hand to the gas space of the electrolysis cells and on the other hand to the inlet of the siphon.

1. (i) der Betriebsdruck auf der Elektrodenseite, bevorzugt der Gasdiffusionselektrodenseite, der Elektrolyseure zwischen Atmosphärendruck und 1 bar Überdruck liegt, bevorzugt in einem Bereich von 100 bis 500 mbar Überdruck liegt, und
2. (ii) der Betriebsdruck auf der Ablaufseite des Rohrleitungssiphons kleiner ist als der Betriebsdruck auf der Zulaufseite dieses Rohrleitungssiphons, bevorzugt zwischen Atmosphärendruck und 100 mbar Überdruck

Particularly preferably suitable is an embodiment of the method according to the invention in which

1. (i) the operating pressure on the electrode side, preferably the gas diffusion electrode side, of the electrolysers is between atmospheric pressure and 1 bar overpressure, preferably in a range from 100 to 500 mbar overpressure, and
2. (ii) the operating pressure on the outlet side of the pipeline siphon is lower than the operating pressure on the inlet side of this pipeline siphon, preferably between atmospheric pressure and 100 mbar overpressure

Expensive controls for automating a changeover from the start-up to the operating pipeline system are avoided by the invention. A separate piping system for liquid and gas removal when starting up is no longer required. The remaining necessary fittings can be dimensioned smaller because only the liquid flow at the pipeline siphon and no longer the two-phase flow of liquid and gas at the outlet header of the electrolyser has to be adjusted/shut off. Possible operating errors and consequential damage to the electrolyser with a manual switchover at the process header are eliminated. According to the invention, the liquid is preferably removed in each operating mode of the electrolysis device according to step a. of the method according to the invention, in particular when starting up, shutting down and during operation of the electrolysis device.

The possibly necessary switchover of the electrolyte feed to the electrolyser from the start-up to the operating piping system is not affected by the change on the outflow side; since only liquid streams need to be switched, switching can be manual or automatic without interruption.

Furthermore, it is not relevant for the change whether in the embodiment of the electrolyzers operated with gas diffusion electrodes, these electrolyzers with a gas diffusion electrode-side gas recycling within the meaning of DE10149779 are equipped or the gas is supplied in a single flow such as in DE102013011298 described, since gas recycling would take place within the limits specified by the gas supply and discharged pressure control.

1. a. zur flüssigkeitsablaufseitigen Entkopplung des Betriebsdrucks der Elektrolyseure von dem Betriebsdruck des Rohrleitungssystems mindestens einer der Flüssigkeitsabfuhren die Flüssigkeitsabläufe aus den Anodenräumen oder den Kathodenräumen oder aus beiden dieser Räume der Elektrolyseure je Elektrolyseur über einen Rohrleitungssiphon in Fluidverbindung mit dem Rohrleitungssystem der Flüssigkeitsabfuhr steht, und
2. b. die Gasableitung aller mit vorgenanntem Rohrleitungssiphon ausgestatteten Elektrolyseure über ein individuelles Regelventil pro Elektrolyseur mit der entsprechenden gemeinsamen Gasabfuhr in Fluidverbindung steht.

Another object of the invention is an electrolysis device, in particular for the production of chlorine, containing a plurality of electrolyzers selected from membrane electrolyzers, with at least each electrolyzer having at least one liquid outlet on the anode side and at least one gas outlet, and separately on the cathode side at least one liquid outlet and at least one gas outlet and the anode chambers of these electrolyzers with one another, and separately the cathode chambers of these electrolyzers are connected to one another at least via a liquid supply, a gas discharge and a liquid discharge, wherein

1. a. for the purpose of decoupling the operating pressure of the electrolyzers from the operating pressure of the pipeline system on the liquid outlet side, at least one of the liquid outlets has liquid outlets from the anode compartments or the cathode compartments or from both of these compartments of the electrolyzers in fluid connection with the pipeline system of the liquid outlet via a pipeline siphon, and
2. b. the gas discharge line of all electrolysers equipped with the aforementioned pipeline siphon is in fluid connection with the corresponding common gas discharge line via an individual control valve for each electrolyser.

The expert understands a "fluid connection" to be a connection between at least two parts of a plant, through which a substance, which can be present in any physical state, can be transported as a material flow from one part of the plant (e.g. pipe siphon) to another part of the plant (e.g. residual gas discharge), for example a pipe .

In a preferred embodiment, the electrolysis device has gas diffusion electrodes on the anode side and/or on the cathode side, particularly preferably on the cathode side, with at least one outflow manifold on the gas diffusion electrode side being present in each electrolyzer, which is in fluid communication with the gas space and the liquid on the gas diffusion electrode side, and which branches into at least one gas discharge line on the gas diffusion electrode side with a control valve and at least one liquid discharge line on the gas diffusion electrode side with a pipeline siphon. This Branching can be implemented very particularly preferably by a pipeline that is routed perpendicularly with a tolerance of ±15°.

In a further embodiment of the method according to the invention, it is considered advantageous if the electrolyzers of the electrolysis device each have a device for pressure regulation, which regulates the operating pressure on the inlet side of the pipeline siphon via the individual control valve of the gas discharge line, preferably on the gas diffusion electrode side, in such a way that a There is overpressure, preferably so that the operating pressure on the outlet side of the pipeline siphon is lower than the operating pressure on the inlet side of the pipeline siphon, preferably between atmospheric pressure and 100 mbar overpressure.

The necessary dimensioning of the pipeline siphon can be determined without further ado by a person skilled in the art for use according to the invention. The height of the pipeline siphon results from the maximum pressure difference between the outlet side of the pipeline siphon, where the pressure is preferably between 0 mbar and 100 mbar overpressure, and the inlet side of the pipeline siphon, where the operating pressure is preferably between 0 mbar and 1 bar overpressure is between 0 mbar and 500 mbar overpressure, as well as the minimum density of the circulation liquid discharged via the pipe siphon on the electrode side. The diameter of the siphon is characterized in that the pressure losses occurring in the siphon can be neglected.

Another object of the invention is the use of a pipeline siphon on the electrode side, preferably on the gas diffusion electrode side, liquid outlet of membrane electrolyzers of an electrolyzer containing several electrolyzers in the form of membrane electrolyzers (preferably with gas diffusion electrodes, in particular with oxygen-consuming cathodes), with at least each electrolyzer has at least one liquid outlet and at least one gas outlet on the anode side, and at least one liquid outlet and at least one gas outlet on the cathode side, and the anode chambers of these electrolyzers are connected to one another and separately the cathode chambers of these electrolyzers are connected to one another via at least one liquid inlet, one gas outlet and one liquid outlet are, to decouple the operating pressure of the electrolysers from the operating pressure of the liquid outlet side the piping system.

It is preferred if the gas space of the pipeline siphon is in fluid communication with the gas outlet of the electrolysis device via a control valve that can be controlled.

If the use involves an electrolysis device containing several electrolyzers in the form of membrane electrolyzers with a gas diffusion electrode, in particular with an oxygen-consuming cathode, the electrolyzers have at least one liquid outlet and at least one gas outlet each on the anode side, and separately on the cathode side at least one liquid outlet and at least one each a gas discharge line, and on the gas diffusion electrode side via a gas supply line, the anode chambers of these electrolyzers being connected to one another and separately the cathode chambers of these electrolyzers to one another being connected to one another at least via said gas inlet, via a liquid inlet, via a gas outlet and via a liquid outlet.

In the use according to the invention, it is preferred if the operating pressure of at least one liquid discharge is lower than the operating pressure of the electrolyzers.

1.1

Gaszufuhr für die Gasdiffusionselektrode, beispielsweise Sauerstoff-haltiges Gas für die Sauerstoffverzehrkathode,

1.11

Armatur zur Gaszufuhr

1.12

Armatur zur Flüssigkeitszufuhr im Normalbetrieb

1.13

Armatur zu den An-/ Abfahrsystemen

1.14

Armatur für ablaufseitiges Rohrleitungssystem der Produktabfuhr im Normalbetrieb

1.15

Armatur für ablaufseitiges Rohrleitungssystem der Produktabfuhr im An-/ Abfahrbetrieb

1.2

Betriebsmediumzufluss für die Kathodenseite während des Normalbetriebes, beispielsweise verdünnte Natronlauge

1.21

in der Gaszufuhr angeordnete Gasstrahlpumpe

1.22

Ventil der Gaszufuhr

1.3

Betriebsmediumzufluss für die Kathodenseite während des An- und Abfahrprozesses, beispielsweise verdünnte Natronlauge

1.4

Abfluss der Restgases der Gasdiffusionselektroden-Reaktion im Normalbetrieb

1.5

Abfluss der Produkt-haltigen Flüssigkeit aus dem Elektrolyseur, z.B. Natronlauge im Normalbetrieb

1.6

Abfluss der Restgases der Gasdiffusionselektroden-Reaktion während des An-/ Abfahrprozesses

1.7

Abfluss der Produkt-haltigen Flüssigkeit aus dem Elektrolyseur, z.B. Natronlauge während des An-/ Abfahrprozesses

1.8

Druckregelung für Restgas (Abgas)

2.1

Gaszufuhr für die Gasdiffusionselektrode, beispielsweise Sauerstoff-haltiges Gas für die Sauerstoffverzehrkathode,

2.11

Ventil der Gaszufuhr

2.12

Ventil zum Betriebsmediumzufluss während des Normalbetriebes

2.13

Ventil zum Betriebsmediumzufluss während des An-/ Abfahrens

2.14

Rohrleitungssiphon

2.15

Absperrventil, z.B. zur Nutzung für Wartungsarbeiten an der Vorrichtung

2.16

Regelventil im Abgassystem der Restgasabfuhr eines Elektrolyseurs

2.2

Betriebsmediumzufluss für die Kathodenseite während des Normalbetriebes, beispielsweise verdünnte Natronlauge

2.21

in der Gaszufuhr angeordnete Gasstrahlpumpe

2.22

Regelventil der Gaszufuhr

2.3

Betriebsmediumzufluss für die Kathodenseite während des An-/ Abfahrens, beispielsweise für verdünnte Natronlauge

2.4

Gasabfuhr des Produktgases und/oder des Restgases für Normalbetrieb und Ab- und Anfahrten

2.5

Flüssigkeitsabfuhr der Flüssigkeit aus dem Elektrolyseur (z.B. aufgestärkte Natronlauge) und dazugehöriges Rohrleitungssystem

3.1

Ablaufsammelleitung des Elektrolyseurs für gemeinsame Abführung von Gas, z.B. Restgas, und Flüssigkeit

3.2

Flüssigkeitsablauf des Elektrolyseurs in Form einer Abflussleitung der Flüssigkeit nach durch Gravitation erfolgter Trennung vom Gas, z.B. Restgas

3.3

Gasableitung des Elektrolyseurs in Form einer Abflussleitung des Gases nach durch Gravitation erfolgter Trennung von der Flüssigkeit

3.4

Flüssigkeitsabfuhr der Flüssigkeit aus dem Elektrolyseur (z.B. aufgestärkte Natronlauge) und dazugehöriges Rohrleitungssystem

3.5

Flüssigkeitspegel im Rohleitungssiphon im An-/ Abfahrbetrieb (gleicher Druck im Elektrolyseur und im ablaufseitigen Rohrleitungssystem)

3.6

Unterschiedliche Flüssigkeitspegel im Rohleitungssiphon beim Normalbetrieb (höherer Druck im Elektrolyseur gegenüber dem ablaufseitigen Rohrleitungssystem)

3.7

Belüftung

3.8

Rohrleitungssiphon

An example of a prior art electrolyzer is shown in FIG Fig.1 shown. For the sake of clarity and without restricting the invention thereto, FIG Fig.2a and Fig.2b each illustrated a possible electrolysis device according to the invention as an example. In Figure 2a is an electrolytic device that is equipped with conventional electrodes (not shown) on the cathode side and does not require a gas supply for the cathodic half-cell reaction. In Figure 2b an electrolysis device is shown which is equipped on the cathode side with gas diffusion electrodes (not shown) which require a gas supply for the cathodic half-cell reaction taking place there. An example of the installation of the pipeline siphon in an electrolysis device according to the invention is given in Fig.3 pictured. For simplification, only the liquid and gas supply and discharge on the cathode side was shown as an example. The connections on the anode side would be analogous. The following reference symbols were used in the figures:

1.1

Gas supply for the gas diffusion electrode, for example oxygen-containing gas for the oxygen-consuming cathode,

1.11

Gas supply fitting

1.12

Fitting for liquid supply in normal operation

1.13

Fitting to the start-up/shutdown systems

1.14

Valve for the downstream pipe system of the product discharge in normal operation

1.15

Fitting for the downstream piping system of the product discharge in start-up/shutdown operation

1.2

Operating medium inflow for the cathode side during normal operation, for example diluted caustic soda

1.21

Gas jet pump arranged in the gas supply

1.22

Gas supply valve

1.3

Operating medium inflow for the cathode side during the start-up and shut-down process, for example diluted caustic soda

1.4

Outflow of the residual gas of the gas diffusion electrode reaction in normal operation

1.5

Outflow of the product-containing liquid from the electrolyser, eg caustic soda in normal operation

1.6

Drainage of the residual gas from the gas diffusion electrode reaction during the startup/shutdown process

1.7

Outflow of the liquid containing the product from the electrolyser, eg caustic soda, during the start-up/shutdown process

1.8

Pressure control for residual gas (exhaust gas)

2.1

Gas supply for the gas diffusion electrode, for example oxygen-containing gas for the oxygen-consuming cathode,

2.11

Gas supply valve

2.12

Valve for operating medium inflow during normal operation

2.13

Valve for operating medium inflow during start-up/shutdown

2.14

pipe siphon

2.15

Shut-off valve, eg to be used for maintenance work on the device

2.16

Control valve in the exhaust system of the residual gas discharge of an electrolyser

2.2

Operating medium inflow for the cathode side during normal operation, for example diluted caustic soda

2.21

Gas jet pump arranged in the gas supply

2.22

Gas supply control valve

2.3

Operating medium inflow for the cathode side during start-up/shutdown, e.g. for diluted caustic soda

2.4

Gas discharge of the product gas and/or the residual gas for normal operation and departures and arrivals

2.5

Liquid discharge of the liquid from the electrolyser (e.g. fortified caustic soda) and associated piping system

3.1

Discharge manifold of the electrolyser for the joint discharge of gas, eg residual gas, and liquid

3.2

Liquid outflow of the electrolyser in the form of an outflow line for the liquid after it has been separated from the gas, eg residual gas, by gravity

3.3

Gas discharge from the electrolyser in the form of a discharge pipe for the gas after separation from the liquid by gravity

3.4

Liquid discharge of the liquid from the electrolyser (e.g. fortified caustic soda) and associated piping system

3.5

Liquid level in the pipeline siphon during start-up/shutdown (same pressure in the electrolyser and in the downstream pipe system)

3.6

Different liquid levels in the pipeline siphon during normal operation (higher pressure in the electrolyser compared to the downstream pipeline system)

3.7

ventilation

3.8

pipe siphon

Figure 2a illustrates an example of an electrolysis device according to the invention, which contains a number of n membrane electrolyzers shown as "electrolyzer 1" to "electrolyzer 2...n", which are each equipped with a normal electrode (not shown), ie no gas diffusion electrode, on the anode side and cathode side. For simplification are in Fig.2a only the gas and liquid connections of the cathode side are shown. Here the electrolyzers are further connected to one another at least via a liquid supply 2.2, gas discharge 2.4 and a liquid discharge 2.5. The liquid discharge takes place on the cathode side of each electrolyzer via a pipeline siphon 2.14 for the liquid discharge-side decoupling of the operating pressure of the electrolyzers from the operating pressure of the subsequent pipeline system of the liquid discharge 2.5. Furthermore, the gas is discharged from all electrolyzers equipped with the aforementioned pipeline siphon 2.14 into the common gas outlet 2.4 via an individual control valve 2.16 provided for each individual electrolyzer. On the anode side, the electrolyzers are also connected to one another at least via a liquid inlet, gas outlet and liquid outlet (not shown).

Figure 2b shows an example of an electrolysis device within the meaning of the invention, which contains a number of n membrane electrolyzers shown as "electrolyzer 1" to "electrolyzer 2...n" with a gas diffusion electrode connected on the cathode side (not shown), the electrolyzers at least having the gas diffusion electrode side Gas supply 2.1, a gas diffusion electrode-side liquid supply 2.2, a gas diffusion electrode-side residual gas discharge 2.4 and a gas diffusion electrode-side liquid discharge 2.5 are connected to one another. Only two electrolysers have been shown for simplicity. For further simplification, in Fig.2b only the gas and liquid connections of the gas diffusion electrode side (ie the cathode side) are shown. The liquid outflow of an electrolyzer on the gas diffusion electrode side takes place via a pipeline siphon 2.14 for decoupling the operating pressure of the electrolyzer from the operating pressure of the subsequent pipeline system 2.5 on the liquid outflow side. Furthermore, the gas discharge on the gas diffusion electrode side of all electrolysers equipped with the aforementioned pipeline siphon 2.14 takes place into the common gas diffusion electrode side residual gas discharge 2.4 via an individual control valve 2.16 provided for each individual electrolyser. On the anode side, the electrolyzers are also connected to one another at least via a liquid inlet, gas outlet and liquid outlet (not shown).

It will be in Fig.2a and 2 B drain side as in Fig.3 shown initially gas (product gas or residual gas) and liquid in the horizontally running discharge manifold 3.1 of the electrolyzer together in the direction of the further piping systems. Gas and liquid then separate due to their density difference in a subsequent branch with an almost vertical pipe run (preferably ±15°); Gas flows upwards through the discharge of residual gas 3.3 in the direction of the pressure control 2.16 assigned to each electrolyzer. The liquid is discharged downwards into the liquid discharge line 3.2.

examples Example 1 (see Fig. 1): Sodium chloride electrolysis with SVK, state-of-the-art design in analogy to conventional chlor-alkali electrolysis without SVK

Several electrolyzers (electrolyzer 1, electrolyzer 2...n), each with an oxygen-consuming cathode connected on the cathode side as a gas diffusion electrode, were operated in parallel. For simplification are in Fig.1 only two electrolysers shown. In the production site used, up to 10 or more electrolysers were operated in parallel. For further simplification, in Fig.1 only the gas and liquid connections of the cathode side are shown.

The raw materials oxygen (1.1) and diluted caustic soda (1.2, 1.3) were distributed from the upstream plants to the electrolyzers via piping systems. On the liquid side, there were separate systems for normal operation (1.2) and start-up/shutdown (1.3), since the start-up/shutdown processes generally follow a pressure/temperature profile that differs from normal operation.

The products of the electrolysis process, the residual gas of the oxygen-depleted cathode reaction (1.4, 1.6) and the sodium hydroxide solution strengthened in the electrolyser (1.5, 1.7) were collected in pipeline systems analogously to the product feed and discharged into the downstream systems. Due to the different pressure levels in normal operation and during start-up/shutdown, separate piping systems were required for normal operation (1.4, 1.5) and start-up/shutdown (1.6, 1.7).

In normal operation, the operating pressure was generally controlled via a central pressure control for the exhaust gas (1.8). The pipe system for liquid removal during normal operation was under the same operating pressure as the electrolysers. The start-up/shutdown operation was generally carried out without pressure at atmospheric pressure.

The amounts fed to the electrolyser and the respective route were adjusted/controlled via valves (1.11, 1.12, 1.13) in the supply line to the electrolyser.

The way for the removal of the products was also set via valves (1.14, 1.15) arranged on the electrolyzer. Since gas and liquid were initially discharged through the same line in the outlet of the electrolysers, the gas and liquid were separated after the valves on the outlet side (1.14, 1.15) by pipes leading away upwards and downwards.

There were two alternative modes of operation for gas-side operation: On "electrolyser 1" of Fig.1 shows the simple flow of oxygen and subsequent removal of the residual gas. To "electrolyser 2...n" of Fig.1 shown the recycling of oxygen-rich residual gas to the supply side via a gas jet pump (1.21) arranged in the gas supply as in DE10149779 described, possibly with an additional control valve (1.22).

An electrolyser was switched from start-up to normal operation in analogy to conventional chlor-alkali electrolysis by first stopping the liquid and gas circulation by closing the valves to the start-up/shutdown systems (1.11, 1.13, 1.15). The pressure was then raised to the operating pressure, e.g. via the gas supply 1.11 or an additional auxiliary gas supply. After that, the liquid and gas circulation on the operating systems (1.11, 1.12, 1.14) could be started again. The descent was carried out analogously in reverse order.

As described above, this mode of operation involves the risk of damage to the oxygen-depleting cathode. In the case of manual conversion, there is a risk of operating errors; the alternative automation with mechanically driven fittings would be expensive since it would be required separately for each electrolyser.

Example 2 (see Fig. 2b): Sodium chloride electrolysis with SVK, design according to the invention with drain siphon

Analogously to the previously described variant in Figure 2b the raw materials oxygen (2.1) and diluted caustic soda (2.2, 2.3) from the upstream systems were distributed to the electrolysers via piping systems. On the liquid side, there were separate systems for normal operation (2.2) and start-up/shutdown (2.3), since the start-up/shutdown processes generally followed a pressure/temperature profile that differed from normal operation. To the simplification are in Fig.2b again, only the gas and liquid connections on the cathode side are shown.

The products of the electrolysis process, the residual gas of the oxygen-depleted cathode reaction (2.4) and the caustic soda strengthened in the electrolyser (2.5) were collected in pipeline systems analogously to the product feed and discharged into the downstream plants.

Due to the solution according to the invention for the pressure separation at the electrolyser, no separate drain pipe systems for the start-up/shutdown operation as in the example above (cf. Fig.1 : 1.6, 1.7) required. The pressure on the gas side was regulated via control valves (2.16) in the line to the exhaust gas system, which were now assigned to each electrolyser. On the liquid side, the fortified caustic soda was able to drain freely via the siphon (2.14) into the downstream pipeline system (2.5), which was to be operated without pressure, regardless of the respective operating pressure. With the valve (2.15), the electrolyser could still be separated from the pipe system for maintenance work.

Analogously to the previously described variant in Fig.1 there are currently two alternative modes of operation for gas-side operation: The simple flow of oxygen and subsequent removal of the residual gas is shown on electrolyser 1. The recycling of oxygen-rich residual gas to the supply side via a gas jet pump (2.21) arranged in the gas supply as in DE10149779 described, possibly with an additional control valve (2.22). In terms of the invention described here, both alternatives can be used equally.

Thanks to the design described, it was no longer necessary to switch valves between start-up/shutdown and normal operation on the outlet side of the electrolyser. An interruption in the liquid supply and the associated switching off of the polarization rectifier were thus avoided. The potential for operating errors has been reduced and the commissioning process has been simplified. Furthermore, the downstream piping systems for the start-up and shut-down processes can be omitted. The switchover that is still required on the inlet side was not critical and could take place in a smooth transition since the inlet side does not have any significant influence on the operating pressure.

Example 3 (see Fig.3): Outlet side of an electrolyzer in the embodiment according to the invention with a siphon

In the outflow manifold (3.1) of the electrolyser, gas and liquid initially flowed together in the direction of the downstream piping systems. Gas and liquid were then separated by their density difference in a subsequent vertical pipeline; Gas flowed upwards (3.3) towards the pressure control associated with each electrolyser (drawing Fig.2a & Fig.2b , 2.16) from; the liquid ran down (3.2).

Due to the inventive design of the draining liquid line as a siphon, the liquid could always drain freely in the direction of the draining pipeline system (3.4), regardless of the operating pressure that was set in each case. During depressurized start-up/shutdown operation, the liquid level on the inlet side of the siphon was at the same level (3.5) as on the outlet side. During normal operation with positive operating pressure, the liquid level in the inlet side of the siphon was lower in accordance with the ratio of operating pressure to liquid density (3.6). Intermediate states could occur freely when the operating pressure was increased from start-up to normal operation or vice versa when shutting down.

In order to enable the gas pressure to be regulated gently, the height of the siphon had to be selected in such a way that no gas could penetrate through the lower end, even at the maximum possible operating pressure.

The further piping system (3.4) was dimensioned in such a way that the liquid can drain freely. Overpressure was avoided, as was underpressure, which could arise, for example, from lifting effects. It is advantageous to design the discharging line as a free level line or an additional ventilation (3.7) that avoids negative pressure.

Claims (13)

Method for operating an electrolysis device with a plurality of electrolyzers selected from membrane electrolyzers, wherein at least each electrolyzer has at least one liquid outlet and at least one gas outlet on the anode side, and separately on the cathode side at least one liquid outlet and at least one gas outlet and the anode chambers of these electrolyzers with one another and separately therefrom the cathode chambers of these electrolysers are connected to each other at least via a liquid supply (2.2), a gas outlet (2.4) and a liquid outlet (2.5), characterized in that the operating pressure of at least one liquid outlet (2.5) is set lower than the operating pressure of the electrolysers and at the same time a. the liquid drains from the anode compartments or the cathode compartments or from both of these compartments of the electrolysers via a pipe siphon (2.14) into the pipe system of the liquid discharge (2.5), whereby with each pipe siphon (2.14) on the liquid discharge side the operating pressure of the electrolysers differs from the lower operating pressure of the subsequent one Pipeline system of the liquid discharge (2.5) is decoupled, and b. each gas discharge of the electrolysers decoupled with a pipe siphon (2.14) is carried out individually for each electrolyser via an individual control valve (2.16) for each electrolyser into the common gas discharge (2.4). Method according to Claim 1, characterized in that the operated electrolysis device contains a plurality of electrolyzers selected from membrane electrolyzers with a gas diffusion electrode, in particular with an oxygen-consuming cathode, these electrolyzers being supplied at least via a gas supply (2.1) on the gas diffusion electrode side, via a liquid supply on the gas diffusion electrode side as liquid supply (2.2 ), a residual gas outlet on the gas diffusion electrode side as a gas outlet (2.4) and a liquid outlet on the gas diffusion electrode side as a liquid outlet (2.5) are connected to one another. Process according to Claim 1 or 2, characterized in that the membrane electrolyzers are selected from alkali metal chloride membrane electrolyzers. Process according to Claim 3, characterized in that the alkali metal chloride used is selected from lithium chloride, sodium chloride, potassium chloride or mixtures thereof. Method according to one of Claims 2 to 4, characterized in that the electrolysers are selected from membrane electrolysers with oxygen-consuming cathodes as the gas diffusion electrode, whose gas supply (2.1) on the gas diffusion electrode side is connected to a source for a gas stream containing oxygen gas. Method according to Claim 2, characterized in that the electrolysers are selected from membrane electrolysers with gas diffusion electrodes whose gas supply (2.1) on the gas diffusion electrode side is connected to a source for a gas flow containing carbon dioxide, in particular for a gas flow of carbon dioxide. Process according to one of Claims 1 to 6, characterized in that the operating pressure of the electrolysers is between atmospheric pressure and 1 bar overpressure, preferably in a range from 100 to 500 mbar overpressure. Method according to one of Claims 1 to 5, characterized in that the operating pressure on the outlet side of the pipeline siphon is lower than the operating pressure on the inlet side, preferably between atmospheric pressure and 100 mbar overpressure. Method according to one of the preceding claims, characterized in that (i) the gas selected from product gas, tail gas, mixture of product gas and tail gas and (ii) the liquid are first led out together as a mixture in an outflow manifold of each individual electrolyzer out of the electrolyzer and this mixture is then subjected to a gas-liquid separation, with the gas being discharged via the gas discharge line according to step b. and the liquid via the liquid outlet according to step a. is effected. Method according to one of the preceding claims, characterized in that the liquid discharge (2.5) in each operating mode of the electrolysis device according to step a. takes place, in particular when starting up, shutting down and during operation of the electrolysis device. Electrolysis device, in particular for the production of chlorine, containing a plurality of electrolyzers selected from membrane electrolyzers, with at least each electrolyzer having at least one liquid outlet on the anode side, at least one gas outlet, and separately on the cathode side at least one liquid outlet and at least one gas outlet, and the anode chambers of these electrolyzers among one another, and separately the cathode chambers of these Electrolyzers are connected to one another at least via a liquid supply (2.2), a gas discharge (2.4) and a liquid discharge (2.5), characterized in that a. for decoupling the operating pressure of the electrolyzers from the operating pressure of the pipeline system on the liquid outlet side, at least one of the liquid outlets (2.5) the liquid outlets from the anode compartments or the cathode compartments or from both of these areas of the electrolyzers for each electrolyzer via a pipeline siphon (2.14) in fluid connection with the pipeline system of the liquid outlet ( 2.5) stands, and b. the gas outlet of all electrolyzers equipped with the aforementioned pipeline siphon (2.14) is in fluid connection with the corresponding common gas outlet (2.4) via an individual control valve (2.16) for each electrolyzer. Electrolysis device, in particular for chlorine production, according to claim 11, characterized in that the electrolysers contain gas diffusion electrodes, preferably on the cathode side, the electrolysers being additionally connected to one another at least via a gas supply (2.1) on the gas diffusion electrode side. Use of a pipeline siphon at the liquid outlet of electrolyzers of an electrolysis device containing several membrane electrolyzers, the electrolyzers being connected to one another at least via a liquid inlet (2.2), a gas outlet (2.4) and a liquid outlet (2.5), for decoupling the operating pressure of the electrolyzers from the operating pressure on the liquid outlet side the subsequent pipeline system of the liquid discharge (2.5).

Images