METHOD FOR CHANGING THE OPERATING MODE OF AN ELECTROLYSIS SYSTEM, AND ELECTROLYSIS SYSTEM

Abstract

A device comprising an electrolyser, a compressor, and a membrane separating device, and to a method for changing the operating mode between normal and standby operation of said device, in the normal operation of which an electrolysis raw product comprising carbon dioxide is converted in the electrolyser into an electrolysis product containing carbon dioxide and carbon monoxide, at least one portion of which is conducted via the compressor and is fed at an increased pressure to the membrane separating device in order to obtain a retentate which is enriched in carbon monoxide and depleted of carbon dioxide compared with the electrolysis product. According to the invention, in order to change from the normal operation into the standby operation, the electrolyser is completely isolated from the membrane separating device in terms of flow and then shut down, wherein the pressure ratios in the membrane separating device are largely maintained.

Claims

1. A method for changing the operating mode of a device comprising an electrolyzer, a compressor, and a membrane separating device between normal and standby operation, wherein, in normal operation of the device, an electrolysis raw product comprising carbon dioxide is converted in the electrolyzer into an electrolysis product containing carbon dioxide and carbon monoxide, at least one portion of which product is conducted via the compressor) and is fed at an increased pressure to the membrane separating device in order to obtain a retentate which is enriched in carbon monoxide and depleted of carbon dioxide, compared with the electrolysis product, wherein, in order to change from normal to standby operation, the electrolyzer is completely isolated from the membrane separating device in terms of flow and then shut down, wherein the pressure ratios in the membrane separating device are largely maintained.

2. The method according to claim 1, wherein, in order to maintain the pressure ratios in the membrane separating device, the compressor is connected to the membrane separating device to form a sealed-in system in terms of flow, in which the suction side of the compressor is connected to the permeate side of the membrane separating device via a first line and is connected to the pressure side of the compressor or the retentate side of the membrane separating device via a second line, wherein the differential pressure between retentate and permeate side is controlled via a control valve arranged in the second line.

3. The method according to claim 1, wherein, in order to change from standby to normal operation, the electrolyzer is started up and its isolation from the membrane separating device in terms of flow is then completely removed, while largely maintaining the pressure ratios in the membrane separating device.

4. The method according to claim 2, wherein, in order to change from standby to normal operation, the system which is sealed-in in terms of flow and comprises the compressor and the membrane separating device is connected to the already-started electrolyzer, wherein, at the same time, the path for the retentate is opened downstream of the membrane separating device, and the direct connections of the suction side of the compressor with and the permeate side of the membrane separating device and the pressure side of the compressor or the retentate side of the membrane separating device are interrupted.

5. A device having a compressor, a membrane separating device, and an electrolyzer, by means of which, during normal operation of the device, an electrolysis raw product comprising carbon dioxide can be converted into an electrolysis product containing carbon dioxide and carbon monoxide, at least one portion of which product can be conducted via the compressor and can be fed at an increased pressure to the membrane separating device in order to obtain a retentate which is enriched in carbon monoxide and depleted of carbon dioxide compared with the electrolysis product, wherein the device has an isolation device with at least one valve with which the electrolyzer can be completely isolated from the membrane separating device in terms of flow when changing from normal to standby operation, while largely maintaining the pressure ratios in the membrane separating device.

6. The device according to claim 5, wherein the isolation device comprises several valves, as well as a first and a second line for connecting the membrane separating device to the compressor to form a sealed-in system, in which the suction side of the compressor is connected to the permeate side of the membrane separating device via the first line and is connected to the pressure side of the compressor or the retentate side of the membrane separating device via the second line, wherein, in the second line, a control device is arranged, via which the differential pressure between retentate and permeate side of the membrane separating device can be controlled when changing the operating mode.

7. The device according to claim 5, wherein the device has a mixing device, arranged upstream of the electrolyzer and connected to the permeate side of the membrane separating device in terms of flow, in which a raw product containing carbon dioxide can be mixed with at least one portion of the permeate obtained in membrane separating device to form the electrolysis raw product, wherein the fluidic connection existing between the permeate side of the membrane separating device and the mixing device comprises a valve, belonging to the isolation device, which is open during normal operation of the device and is closed in standby operation.

8. The device according to claim 5, wherein the electrolyzer is a high-temperature or low-temperature electrolyzer designed to electrochemically convert carbon dioxide—alone or together with water—to hydrogen and/or carbon monoxide.

Description

[0032] The invention is explained in more detail below using an exemplary embodiment schematically illustrated in FIG. 1.

[0033] FIG. 1 shows two preferred embodiments of the device according to the invention, in which the membrane separating device and the compressor can be connected to one another in a first or a second manner when changing between normal and standby operation.

[0034] In device B, a carbon dioxide-containing raw product 1 is introduced into mixing device A in normal operation and is there mixed with the recycle stream 2, which is largely composed of carbon dioxide, to form the electrolysis raw product 3, which is then supplied to electrolyzer E. Here, the carbon dioxide contained in electrolysis raw product 3 is reacted—alone or together with water—by high-temperature or low-temperature electrolysis, so that an electrolysis product 4 can be withdrawn from the cathode of electrolyzer E, which consists of carbon dioxide and possibly hydrogen as well as unreacted carbon dioxide. The electrolysis product is supplied via valve a and line 5 to the compressor V, whence it is fed at an elevated pressure into the membrane separating device T via line 6. Although the membrane separating device T is shown with a single membrane M, it may also have several membranes arranged in series or in parallel which are selectively permeable to carbon dioxide. Between the retentate side and the permeate side of each membrane, a pressure difference exists, as a result of which carbon dioxide is separated from the electrolysis product, such that a permeate 7, largely consisting of carbon dioxide, and a retentate 8 depleted in terms of carbon dioxide content compared to the electrolysis product are obtained. The permeate 7 is fed as recycle stream 2 to the mixing device A via valve b, while the permeate 7 is delivered as product 9 to a consumer (not shown) via valve c. Valve d is closed during normal operation, such that nothing flows through line 10. To control the pressure ratios in the membrane separating device T, line 11 (first preferred embodiment) or 12 (first preferred embodiment) contains a control valve e or f that is coupled to a pressure regulator.

[0035] In order to change the device from normal to standby operation, the valves a, b, and c are closed via membrane M or membranes M of the membrane separating device T when the compressor V is running, while largely maintaining the differential pressure. At the same time, valve d is opened, such that the permeate side of the membrane separating device T is connected to the suction side of the compressor V via line 10. The membrane separating device T is now connected to the compressor V to form a sealed-in system and is completely isolated from the electrolyzer E in terms of flow, which can therefore be switched off. The pressure ratios in the membrane separating device T are controlled via control valve e or f during switching and for the duration of standby operation.

[0036] When wanting to change again from standby to normal operation, valves a, b, and c are opened and valve d is closed, while the pressure ratios in the membrane separating device T are largely maintained via control valve e or f. At the same time, electrolyzer E is started again. If necessary, the retentate stream 8 is discarded or returned to the electrolyzer E until the required product purity is achieved.