METHOD AND INSTALLATION FOR THE ELECTROLYTIC PRODUCTION OF LIQUID HYDROGEN

Abstract

The invention relates to a method (100) for the electrolytic production of a liquid hydrogen product (4), in which a water-containing feed is subjected to an electrolysis (E) while receiving an anode raw gas (3), rich in oxygen and containing hydrogen, and a cathode raw gas (2) which is depleted of oxygen and rich in hydrogen, wherein the cathode raw gas (2) downstream of the electrolysis (E) is subjected to a purification (R), a compression (K), and a liquefaction (L), characterized in that the cathode raw gas (2) at least partially undergoes intermediate storage (Z) downstream of the electrolysis (E) and upstream of the liquefaction (L). A corresponding installation is also proposed.

Claims

1. A method (100) for the electrolytic production of a liquid hydrogen product (4), in which a water-containing feed is subjected to an electrolysis (E) while receiving an anode raw gas (3), rich in oxygen and containing hydrogen, and a cathode raw gas (2) which is depleted of oxygen and rich in hydrogen, wherein the cathode raw gas (2) downstream of the electrolysis (E) is subjected to a purification (R), a compression (K), and a liquefaction (L), wherein the cathode raw gas (2) downstream of the electrolysis (E) and upstream of liquefaction (L) is subjected at least partially to intermediate storage (Z), characterized in that the electrolysis (E) is carried out at two different pressure levels, and the cathode raw gas (2) of the electrolysis (E) which is carried out at a higher pressure level is at least partially subjected to intermediate storage (Z), and the cathode raw gas (2) of the electrolysis (E) which is carried out at a lower pressure level is not subjected to intermediate storage (Z).

2. The method (100) according to claim 1, wherein the intermediate storage (Z) takes place at a temperature level in a range of 250 to 330 K, and in particular 273 to 313 K, and a pressure level in a range of 1 to 20 MPa or at a temperature level in a range of 50 to 100 K, and in particular 75 to 100 K, and a pressure level of 1 to 20 MPa, and in particular 3 to 10 MPa.

3. The method (100) according to claim 1, wherein intermediate storage (Z) is carried out upstream and/or downstream of the purification (R).

4. The method (100) according to claim 1, wherein the cathode raw gas (2) upstream of the intermediate storage (Z) is subjected to compression.

5. The method (100) according to claim 1, wherein the purification (R) comprises at least one of the group consisting of a catalytic conversion of oxygen to water, an adsorption, a distillative separation, and a scrubbing with an absorption fluid.

6. The method (100) according to claim 1, wherein the electrolysis (E) is operated as a function of an external energy supply, such that, with a high supply, a high electrolysis output is set, and, with a low supply, a low electrolysis output is set.

7. The method (100) according to claim 6, wherein the electrolysis output is adapted to the external energy supply at a rate of change of (in each case in relation to a maximum output of the electrolysis) more than 1%/min—in particular, more than 0.1%/s, and particularly preferably more than 1%/s—and/or a liquefaction output is adapted more slowly to the external energy supply than is the electrolysis output, and in particular at a rate of (in each case in relation to a maximum output of the liquefaction) less than 5%/min, and in particular less than 2%/min.

8. An installation for producing a liquid hydrogen product (4), comprising: an electrolysis unit with at least one electrolyzer, a purification unit which is designed to enrich with hydrogen a cathode raw gas (2) produced in the electrolysis unit and to at least partially deplete it in other components, a liquefaction unit which is designed to liquefy (L) a gas stream rich in hydrogen, and an intermediate storage, which is arranged downstream of the electrolysis unit and upstream of the liquefaction unit and is designed to store at least part of the raw cathode gas (2) produced in the electrolysis unit, characterized in that the electrolysis unit is set up to produce cathode raw gas (2) at two different pressure levels and is connected to the intermediate storage in such a way that only the cathode raw gas (2) available at a higher pressure level can be fed at least partially to the intermediate storage.

9. The installation according to claim 8, further comprising means which enable the installation to carry out a method (100) for the electrolytic production of a liquid hydrogen product (4), in which a water-containing feed is subjected to an electrolysis (E) while receiving an anode raw gas (3), rich in oxygen and containing hydrogen, and a cathode raw gas (2) which is depleted of oxygen and rich in hydrogen, wherein the cathode raw gas (2) downstream of the electrolysis (E) is subjected to a purification (R), a compression (K), and a liquefaction (L), wherein the cathode raw gas (2) downstream of the electrolysis (E) and upstream of liquefaction (L) is subjected at least partially to intermediate storage (Z), characterized in that the electrolysis (E) is carried out at two different pressure levels, and the cathode raw gas (2) of the electrolysis (E) which is carried out at a higher pressure level is at least partially subjected to intermediate storage (Z), and the cathode raw gas (2) of the electrolysis (E) which is carried out at a lower pressure level is not subjected to intermediate storage (Z); and, wherein the intermediate storage (Z) takes place at a temperature level in a range of 250 to 330 K, and in particular 273 to 313 K, and a pressure level in a range of 1 to 20 MPa or at a temperature level in a range of 50 to 100 K, and in particular 75 to 100 K, and a pressure level of 1 to 20 MPa, and in particular 3 to 10 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further features and advantages of the invention or advantageous developments thereof are explained in more detail below with reference to the attached drawing, wherein

[0032] FIG. 1 is a simplified view of an advantageous development of concepts according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] As already explained at the outset, the invention relates both to a method and to an installation for the electrochemical production of a liquid hydrogen product. The schematic representation in FIG. 1 can be interpreted both as an installation and as a flowchart of a method. If, therefore, an installation component is described below, the statements will also apply analogously to a method step carried out in this installation component, and vice versa. For this reason, the reference signs are also used below to designate method steps which are carried out in corresponding installation parts, and vice versa.

[0034] An advantageous development of the invention is shown schematically In FIG. 1 and denoted as a whole by 100.

[0035] An installation 100 comprises an electrolysis unit E, a cooling and/or compression unit K, a purification unit R, an intermediate storage Z, and a liquefaction unit L.

[0036] Such an installation 100 can also be integrated into one or more containers, such as are usually used for transportation purposes by land and sea, which can thus be transported and set up very quickly and cost-effectively.

[0037] Accordingly, the method comprises an electrolysis step E, a cooling and/or compression step K, a purification step R, an intermediate storage Z, and a liquefaction step L.

[0038] In the electrolysis E, a water-containing feed 1 is converted, using electrical energy, into a hydrogen-containing cathode raw gas 2 and an oxygen-containing anode raw gas 3. In addition to water, the feed 1 can contain additional components—in particular, electrolytes such as, for example, alkaline, acidic, or neutral salts or ions. The feed 1 can, in particular, be fed into the electrolysis unit E on the anode side.

[0039] The cathode raw gas 2 is taken from the electrolysis unit E and is fed into a post-processing stage, which, in a suitable sequence, comprises compression, purification, intermediate storage, and liquefaction. The liquefaction in each case forms the conclusion of the post-processing, and the remaining steps can be varied in their sequence.

[0040] The cooling or compression K of the cathode raw gas 2 can be carried out using a conventional mechanical chiller, or, particularly advantageously, using waste heat from the electrolysis E by means of an absorption chiller or adsorption chiller, which has a particularly advantageous effect on the total energy balance of the installation 100. Even conventional mechanical chillers can utilize waste heat from the electrolysis E, wherein these can initially be used for carrying out volume work, e.g., by steam generation in combination with a turbine for compressing the cathode raw gas 2.

[0041] Various methods are available for purification R—for example, (in particular, cryogenic) adsorption, oxidative combustion of oxygen, condensation of components with comparatively high boiling points, and so on.

[0042] Purification requirements can be significantly reduced if the feed 1 has already been stripped of impurities upstream of the electrolysis E, or depleted thereof. Particularly relevant in this context are gases, e.g., nitrogen, carbon dioxide, and/or noble gases, dissolved in the water of the feed 1. These can, for example, be expelled or otherwise removed from the feed 1 by so-called stripping, using the anode raw gas 3 produced in the electrolysis, or by other degassing strategies such as, for example, membrane degassing.

[0043] The intermediate storage Z can be implemented, for example, at a constant volume using a pressure tank, wherein the pressure tank can be operated at a pressure level which corresponds to a cathode-side, electrolysis pressure level or is filled by means of a compressor with cathode raw gas 2, which can lie at a pressure level above the cathode-side pressure level. Units arranged downstream of the storage tank can in particular be designed such that they can be operated with variable input pressures, or a pressure regulator can be provided downstream of the intermediate storage Z, which ensures a constant pressure.

[0044] Within the scope of the invention, it is also possible to use storage tanks with a constant pressure as the intermediate storage Z. Such storage tanks have, for example, a variable volume (for example, in the form of a plunger or piston in a hollow cylinder or the like), or they can regulate the pressure by appropriate control of the storage temperature.

[0045] In addition, metal hydride storage tanks can be used in which a metal, e.g., an alloy containing palladium, is capable of absorbing hydrogen to form a metal hydride. If such a metal hydride storage tank is used, the release or delivery of hydrogen stored in the intermediate storage Z can, in turn, take place using waste heat from the electrolysis E, with corresponding energy advantages.

[0046] To further increase the dynamics—particularly in the region of the post-processing downstream of the electrolysis E—the respective components can also be operated in parallel to one another in a multiple embodiment, so that a larger controllable range is available. For example, several compressors and/or turbines can be provided for compression, so that the liquefaction output can be reduced to, for example, below 30% of nominal output, by completely switching off at least one component that is present several times.

[0047] As mentioned at the outset, it is advantageous to control the output of the installation 100 as a function of an external energy supply. For example, such an installation 100 can be operated with renewable electrical energy—for example, from a wind farm or a wind park. In the event of a calm, there will accordingly be little or no output available, so that electrolysis may be massively reduced in such a case. In the event that no electrical energy is available, a portion of the generated hydrogen, e.g., from the intermediate storage Z, can be used for generating electrical energy in order to continue to operate the electrolysis E at a minimum output level—for example, 10% of nominal output. Use of hydrogen which evaporates in a liquid tank downstream of the liquefaction L can also be suitable for such use. As a result, it is possible to ensure a more rapid restart or increase in electrolysis output with an increasing external energy supply, i.e., for example, with a stronger wind. In comparison to this, it takes considerably longer to run up an electrolysis unit E that has been taken out of operation—in particular, since the electrolysis unit E must be brought up to an operating temperature. In this case, such an installation 100 can in principle be integrated directly into a wind power installation (e.g., an offshore wind farm)—for example, in order to minimize power transmission losses. Liquid hydrogen and/or cold gases generated by the wind turbine can here be used in part also for cooling the wind turbine (for example, the generator), e.g., in order to minimize the power transmission losses by using superconducting materials.

[0048] To further increase the energy efficiency, a conventional heat exchanger can be used, in which the use of anode raw gas 3 and/or cathode raw gas 2 removed from electrolysis E is heated.

[0049] The anode raw gas 3 can likewise be fed into a processing facility, so that, here too, the steps of purification, drying, compression, liquefaction, and/or storage can be provided. Alternatively, the anode raw gas can be discharged to the surrounding atmosphere, since it does not in principle contain any harmful components, and is therefore harmless in terms of health and environment.