METHOD AND SYSTEM FOR PRODUCING A GAS PRODUCT CONTAINING CARBON MONOXIDE

Abstract

The invention relates to a method (100, 200) for producing a gas product (D) containing at least carbon monoxide, in which method at least carbon dioxide is subjected to an electrolysis process (10) in order to obtain a raw gas (A) containing at least carbon monoxide and carbon dioxide and the carbon dioxide contained in the raw gas (A) is partially or completely fed back to the electrolysis process (10), characterized in that the raw gas (A) is partially or completely subjected to an adsorption process (20) in order to obtain the gas product (D), which is enriched in carbon monoxide and depleted of carbon dioxide in comparison with the raw gas (A), and a residual mixture (E), which is depleted of carbon monoxide and enriched in carbon dioxide in comparison with the raw gas (A), and that the residual mixture (E) is at least partially subjected to a membrane separation process (30) in order to obtain a first gas mixture (B) as a retentate and a second gas mixture (H) as a permeate, the first gas mixture (B) at least partially being fed back to the adsorption process (20) together with the raw gas (A) or with the portion thereof subjected to the adsorption process (20), and the second gas mixture (H) at least partially being fed back to the electrolysis process (10). The invention further relates to a corresponding system.

Claims

1. Method (100, 200) for producing a gas product (D) containing at least carbon monoxide, in which method at least carbon dioxide is subjected to an electrolysis process (10) in order to obtain a raw gas (A) containing at least carbon monoxide and carbon dioxide, and the carbon dioxide contained in the raw gas (A) is partially or completely fed back to the electrolysis process (10), characterized in that the raw gas (A) is partially or completely subjected to an adsorption process (20) in order to obtain the gas product (D), which is enriched in carbon monoxide and depleted of carbon dioxide in comparison with the raw gas (A), and a residual mixture (E), which is depleted of carbon monoxide and enriched in carbon dioxide in comparison with the raw gas (A), and that the residual mixture (E) is at least partially subjected to a membrane separation process (30) in order to obtain a first gas mixture (B) as a retentate and a second gas mixture (H) as a permeate, the first gas mixture (B) being at least partially fed back to the adsorption process (20) together with the raw gas (A) or with the fraction thereof subjected to the adsorption process (20), and the second gas mixture (H) being at least partially fed back to the electrolysis process (10).

2. Method (100, 200) according to claim 1, wherein the adsorption process (20) comprises a pressure swing adsorption process and/or a temperature swing adsorption process.

3. Method (100, 200) according to claim 1, wherein the first gas mixture (B) is enriched in carbon monoxide and depleted of carbon dioxide in comparison with the residual mixture (E), and the second gas mixture (H) is depleted of carbon monoxide and enriched in carbon dioxide in comparison with the residual mixture (E).

4. Method (500) according to claim 1, wherein the membrane separation process (30) comprises at least two membrane separation steps, the first gas mixture comprising retentate fractions, each formed in the at least two membrane separation steps, and the second gas mixture comprising permeate fractions, each formed in the at least two membrane separation steps.

5. Method (100-300) according to claim 1, wherein a portion of the residual mixture is discharged from the method (100-300).

6. Method (100-300) according to claim 1, wherein a first fraction of the raw gas (A) is fed to the adsorption process (20), and a second fraction of the raw gas (A) is fed back to the electrolysis process (10), bypassing the adsorption process (20).

7. Method (100-300) according to claim 1, wherein the electrolysis process (10) takes place at an electrolysis pressure level, and the adsorption process (20) takes place at an adsorption pressure level.

8. Method according to claim 7, wherein the adsorption pressure level differs by no more than 1, 2, 3, or 5 bar from the electrolysis pressure level, the residual mixture (E) and/or the first and/or the second gas mixtures (B, H) being compressed to the electrolysis pressure level.

9. Method according to claim 7, wherein the adsorption pressure level is 5 to 30 bar above the electrolysis pressure level, the raw gas (A) or the fraction thereof subjected to the adsorption process (20) being compressed to the adsorption pressure level.

10. Method (100-300) according to claim 1, wherein synthesis gas is formed as the gas product (D), the gas product (D) containing 20 to 100% carbon monoxide and 0 to 80% hydrogen and being poor in or free of carbon dioxide.

11. Method (100-300) according to claim 1, wherein the raw gas (A) has a content of 0 to 60% hydrogen, 10 to 90% carbon monoxide, and 10 to 80% carbon dioxide in the non-aqueous fraction.

12. Method (100-500) according to claim 1, wherein the electrolysis process (10) in the form of a high-temperature electrolysis process using one or more solid oxide electrolysis cells and/or a low-temperature co-electrolysis process is carried out on a liquid electrolyte.

13. System for producing a gas product (D) containing at least carbon monoxide, comprising an electrolysis unit configured to subject at least carbon dioxide to an electrolysis process (10) in order to obtain a raw gas (A) containing at least carbon monoxide and carbon dioxide, and comprising means configured to feed the carbon dioxide present in the raw gas (A) partially or completely back to the electrolysis process (10), characterized by means configured to partially or completely subject the raw gas (A) to an adsorption process (20) in order to obtain the gas product (D), which is enriched in carbon monoxide and depleted of carbon dioxide in comparison with the raw gas (A), and a residual mixture (E), which is depleted of carbon monoxide and enriched in carbon dioxide in comparison with the raw gas (A), means configured to at least partially subject the residual mixture (E) to a membrane separation process (30) in order to obtain a first gas mixture (B) as a retentate and a second gas mixture (H) as a permeate, means configured to at least partially feed the first gas mixture (B) back to the adsorption process (20) together with the raw gas (A) or with the fraction thereof subjected to the adsorption process (20), and means configured to feed the second gas mixture (H) at least partially back to the electrolysis process (10).

14. System according to claim 13, comprising means configured to carry out a method (100, 200) for producing a gas product (D) containing at least carbon monoxide, in which method at least carbon dioxide is subjected to an electrolysis process (10) in order to obtain a raw gas (A) containing at least carbon monoxide and carbon dioxide, and the carbon dioxide contained in the raw gas (A) is partially or completely fed back to the electrolysis process (10), characterized in that the raw gas (A) is partially or completely subjected to an adsorption process (20) in order to obtain the gas product (D), which is enriched in carbon monoxide and depleted of carbon dioxide in comparison with the raw gas (A), and a residual mixture (E), which is depleted of carbon monoxide and enriched in carbon dioxide in comparison with the raw gas (A), and that the residual mixture (E) is at least partially subjected to a membrane separation process (30) in order to obtain a first gas mixture (B) as a retentate and a second gas mixture (H) as a permeate, the first gas mixture (B) being at least partially fed back to the adsorption process (20) together with the raw gas (A) or with the fraction thereof subjected to the adsorption process (20), and the second gas mixture (H) being at least partially fed back to the electrolysis process (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 illustrates a method according to an embodiment of the invention;

[0047] FIG. 2 illustrates a method according to an embodiment of the invention; and

[0048] FIG. 3 illustrates a method not according to the invention.

[0049] In the figures, method steps, technical units, apparatuses, and the like that correspond to one another in terms of function and/or design or structure are denoted by identical reference signs and, for the sake of clarity, are not explained again. Although methods according to embodiments of the invention are illustrated in the drawings and will be explained in more detail below, the corresponding explanations apply similarly to systems configured according to embodiments of the invention. As a result, where method steps are explained hereafter, these explanations apply similarly to system parts.

DETAILED DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 schematically illustrates a method according to an embodiment of the invention, which is denoted overall by 100.

[0051] An electrolysis process 10 is provided as an essential method step of the method 100, which can be carried out, in particular, in the form of HT co-electrolysis using one or more solid oxide electrolysis cells and/or LT co-electrolysis on an aqueous electrolyte, as was explained at the outset in each case. Mixed forms of such electrolysis techniques can also be used within the scope of the present invention. In particular, the electrolysis process 10 may be carried out using one or more electrolysis cells, groups of electrolytic cells, and the like. A feed in the form of a material flow K supplied to the electrolysis process 10 is explained below. This feed comprises carbon dioxide, which is partially converted to carbon monoxide in the electrolysis process 10. In this way, using the electrolysis process 10, a raw gas A is obtained, having a composition that depends on the feeds supplied to the electrolysis process 10 and the electrolysis conditions.

[0052] Within the scope of the embodiment of the present invention illustrated in FIG. 1, a water or vapor flow H.sub.2O is also fed to the electrolysis process 10, wherein the water thus provided is also reacted in the electrolysis process 10 (see, for example, reaction equation 3 in the introductory part). In this way, an oxygen-rich material flow O.sub.2 can be removed from the anode side, and carbon monoxide and hydrogen are formed on the cathode side and in this way pass into the raw gas A.

[0053] The raw gas A contains hydrogen, carbon monoxide, and carbon dioxide. The hydrogen and carbon monoxide present in raw gas A are target products of the method 100. The carbon dioxide present in the raw gas A is the carbon dioxide that was fed to the electrolysis process 10, but was not converted there.

[0054] In the example shown, the raw gas A contains, for example, approximately 31% hydrogen, 32% carbon monoxide, and 37% carbon dioxide. In the example shown, it is formed, for example, in an amount of 177 standard cubic meters per hour and fed completely to a pressure swing adsorption process 20. The raw gas A is present at a pressure of approximately 20 bar, for example. In the example shown, the electrolysis process 10 is carried out at, for example, a temperature of 30 C. The temperatures used in a corresponding electrolysis process 10 are, for example, in a range of approximately 20 to 80 C. Complete conversion of the carbon dioxide during the electrolysis process 10 is generally not desirable in order to protect the electrolysis material, or is not possible in terms of the reaction kinetics, whereby unreacted carbon dioxide is present in the raw gas A.

[0055] During the pressure swing adsorption process 20, the raw gas A is processed together with a retentate mixture B of a membrane method 30, with which the raw gas A is combined beforehand to form a collection flow C. The retentate mixture B is provided, for example, in an amount of approximately 30 standard cubic meters per hour. It contains, for example, approximately 0.1% hydrogen, 80% carbon monoxide, and 20% carbon dioxide. The collection flow C is therefore present in an amount of, for example, approximately 207 standard cubic meters per hour. It contains, for example, approximately 27% hydrogen, 39% carbon monoxide, and 35% carbon dioxide.

[0056] During the pressure swing adsorption process 20, a gas product D and a residual mixture E are formed. For example, the gas product D is provided in an amount of approximately 100 standard cubic meters per hour. It contains, for example, approximately 50% hydrogen, 50% carbon monoxide, and 100 ppm carbon dioxide. For example, the residual mixture E is provided in an amount of approximately 107 standard cubic meters per hour. It contains, for example, approximately 5% hydrogen, 28% carbon monoxide, and 67% carbon dioxide. In other words, the predominant fraction of the hydrogen passes from the collection flow C into the gas product, whereas the predominant fraction of the carbon dioxide passes into the residual mixture E. The residual mixture E is provided at a pressure level of approximately 1.2 bar, for example.

[0057] A portion of the residual mixture E, illustrated here in the form of a material flow F, may be discharged from the process 100 (purge) to prevent an accumulation of inert-behaving components. The remainder is compressed in the form of a material flow G in one or more compressors 40.

[0058] The material flow G is processed at a pressure level of approximately bar, for example, to obtain the aforementioned retentate mixture B, which is enriched in carbon monoxide and depleted of carbon dioxide and hydrogen in comparison with the residual mixture E, and a permeate mixture H, which is depleted of carbon monoxide and enriched in carbon dioxide and hydrogen in comparison with the residual mixture E. The permeate mixture H is provided, for example, at a pressure level of approximately 2 bar. The amount thereof is, for example, approximately 77 standard cubic meters per hour, the content of hydrogen thereof is, for example, approximately 6%, that of carbon monoxide is, for example, approximately 8%, and that of carbon dioxide is, for example, approximately 85%. The pressure level of the retentate mixture B is, for example, approximately 20 bar. Alternatively, it is also possible to use a membrane which retains hydrogen and carbon monoxide and preferably allows carbon dioxide to pass.

[0059] In the embodiment shown in FIG. 1, the permeate mixture H is recompressed in one or more compressors 50 and fed back to the electrolysis process 10 together with a fresh feed flow I as collection flow K. The fresh feed flow I is provided, for example, in an amount of approximately 50 standard cubic meters per hour, and the carbon dioxide content thereof is, for example, over 99.9%. In addition, an amount of 50 standard cubic meters per hour of water or steam is also required here for a desired gas product. The amount of collection flow K is therefore, for example, approximately 128 standard cubic meters per hour. The collection flow K contains, for example, approximately 4% hydrogen, 5% carbon monoxide, and 91% carbon dioxide.

[0060] So as to set the temperature in the electrolysis process 10 and other process steps, a heat exchange, for example, can be carried out upstream and/or downstream of the electrolysis process 10, which can be realized both as a feed-effluent exchanger with heat exchange between the inlet flow K and raw gas flow A, and also by means of external heat media. This is not illustrated in FIG. 1. A water separation process is also not illustrated, within the scope of which water vapor present in the raw gas A can be condensed out and, if necessary, fed back to the electrolysis process 10. After such a water separation process, renewed heatingtypically by approximately 5 to 20 C.can also be carried out upstream of the pressure swing adsorption process 20 so that the temperature level of the raw gas A is above the dew point.

[0061] So as to reduce possible oxygen fractions in the gas product D, a catalytic deoxo reactor can also be installed in the flow of raw gas A in order to remove oxygen. By selecting suitable catalysts, hydrogen oxidizes to water starting at 70 C., for example, and carbon monoxide oxidizes to carbon dioxide starting at 150 C. This also applies to the methods 200 and 300 explained below.

[0062] FIG. 2 schematically illustrates a method according to a further embodiment of the invention, which is denoted overall by 200.

[0063] The method 200 illustrated in FIG. 2 differs, in particular, from the method 100 illustrated in FIG. 1 in that a portion of the raw gas A, as illustrated here in the form of a material flow L, is fed back directly to the electrolysis process 10, i.e., is not subjected to the pressure swing adsorption process 20, but is fed to the material flow H or K. In other words, here (only), a first fraction of the raw gas A is combined with the retentate mixture B and subjected to the pressure swing adsorption process 20, whereas a second fraction of the raw gas A is fed back directly to the electrolysis process 10.

[0064] The fraction of carbon monoxide in the material flow K fed to the electrolysis process 10 can be increased by appropriate partial recirculation. In this way, the content of carbon monoxide in the electrolysis raw product, and thus the raw gas A, can be increased. This may have a positive effect on the overall separation sequence of the method 200. Since only the pressure loss of the electrolysis unit in which the electrolysis process 10 is carried out has to be overcome for appropriate recirculation, an inexpensive fan can be used as the compressor 60.

[0065] FIG. 3 schematically illustrates a method not according to the invention, which is denoted overall by 300.

[0066] The method 300 illustrated in FIG. 3 differs, in particular, from the method 200 previously explained and illustrated in FIG. 2 in that no membrane separation process 30 is carried out here. The compressor 50 can also be dispensed with in this way. Thus, no retentate mixture B is formed here. Instead, a material flow denoted by M here, and a material flow denoted by N here, are formed as partial flows of the same material composition. The material flow M is used like the retentate flow B of the methods 100 and 200 illustrated in FIGS. 1 and 2, and the use of the material flow N corresponds to that of the material flow H in these methods 100 and 200.