METHOD AND PLANT FOR THE ELECTROCHEMICAL PRODUCTION OF OXYGEN

Abstract

The invention relates to a method for producing a gas product containing oxygen, wherein a feedstock containing water is subjected to electrolysis to obtain a raw anode gas, which is rich in oxygen and contains hydrogen, and a raw cathode gas, which is low in oxygen and rich in hydrogen. The raw anode gas is at least partially subjected to a catalytic conversion of hydrogen to water to obtain a first mixture with depleted hydrogen content. A first part of the first mixture is returned to the raw anode gas downstream of the electrolysis and upstream of the catalytic conversion, and the gas product containing oxygen is formed using at least a second part of the first mixture. The invention also relates to a plant for carrying out a method of this type.

Claims

1. A method for producing a gas product containing oxygen, wherein a feedstock containing water is subjected to electrolysis to obtain a raw anode gas, which is rich in oxygen and contains hydrogen, and a raw cathode gas, which is low in oxygen and rich in hydrogen, wherein the raw anode gas is at least partially subjected to a catalytic conversion of hydrogen to water to obtain an intermediate mixture with depleted hydrogen content, that a first part of the intermediate mixture is returned to the raw anode gas downstream of the electrolysis and upstream of the catalytic conversion, and that the gas product containing oxygen is formed using at least a second part of the intermediate mixture.

2. A method according to claim 1, wherein the intermediate mixture is at least partially subjected to condensation to obtain an intermediate mixture fraction with depleted water content, and a condensate, which is rich in water.

3. A method according to claim 2, wherein at least a part of the intermediate mixture fraction is subjected to drying to obtain the gas product, which contains oxygen, and a residual gas with depleted oxygen content and enriched water content.

4. A method according to claim 1, wherein the first part of the intermediate mixture, which is returned to the raw anode gas, is formed using at least a quantitative proportion of the intermediate mixture and/or of the intermediate mixture fraction and/or of the residual gas and/or of the gas product.

5. A method according to claim 1, wherein the first part of the intermediate mixture is returned to the raw anode gas or the anode-side feedstock in an amount which is measured such that a hydrogen concentration in the raw anode gas downstream of the return is at most 0.1%, 0.2%, 0.3%, 0.5%, 1%, or 2%.

6. A method according to claim 3, wherein the drying comprises a temperature swing adsorption (TSA).

7. A method according to claim 3, wherein the intermediate mixture fraction is subjected to a compression upstream of the drying and, to obtain a further intermediate mixture fraction and a further condensate, to a further condensation.

8. A method according to claim 1, wherein at least one of the condensates together with the feedstock is partially or completely returned to the electrolysis.

9. A method according to claim 1, wherein, downstream of the electrolysis and/or in the catalytic conversion, one or more process parameters, comprising a hydrogen concentration and/or a gas temperature and/or a difference between two gas temperatures and/or a gas pressure, are detected, and wherein the first part of the first mixture i) is returned to the raw anode gas when the one or more process parameters are above a predetermined threshold value; or ii) is returned in an amount controlled continuously using the detected process parameters.

10. A method according to claim 9, wherein raw anode gas is discharged from the process when the one or more process parameters—in particular, the difference between two gas temperatures—exceed a predetermined limit value.

11. A method according to claim 1, wherein the electrolysis and/or the catalytic conversion is operated at a pressure level at which the drying is also operated; and/or wherein the part of the first mixture returned to the raw anode gas is compressed to the pressure level at which the catalytic conversion is operated.

12. A method according to claim 1, wherein the raw anode gas is heated in a heat exchanger against the first mixture.

13. A plant for producing a gas product containing oxygen with an electrolysis unit configured to subject a feedstock containing water to electrolysis to obtain a raw anode gas, which is rich in oxygen and contains hydrogen, and a raw cathode gas, which is low in oxygen and rich in hydrogen, wherein a catalytic conversion unit configured, using at least a part of the raw anode gas, to subject to a catalytic conversion of hydrogen to water to obtain an intermediate mixture with depleted hydrogen content by means configured to return a first part of the intermediate mixture to the raw anode gas downstream of the electrolysis and upstream of the catalytic conversion, and to form the gas product containing oxygen using a second part of the intermediate mixture.

14. A plant according to claim 13, further comprising means configured to perform a method for producing a gas product containing oxygen, wherein a feedstock containing water is subjected to electrolysis to obtain a raw anode gas, which is rich in oxygen and contains hydrogen, and a raw cathode gas, which is low in oxygen and rich in hydrogen, wherein the raw anode gas is at least partially subjected to a catalytic conversion of hydrogen to water to obtain an intermediate mixture with depleted hydrogen content, that a first part of the intermediate mixture is returned to the raw anode gas downstream of the electrolysis and upstream of the catalytic conversion, and that the gas product containing oxygen is formed using at least a second part of the intermediate mixture, wherein the intermediate mixture is at least partially subjected to condensation to obtain an intermediate mixture fraction with depleted water content, and a condensate, which is rich in water.

Description

DESCRIPTION OF THE FIGURES

[0042] Further advantages, embodiments, and further details of the present invention are described in more detail below with reference to the accompanying figures, wherein

[0043] FIG. 1 shows, in the form of a schematic block diagram, an advantageous embodiment of a method according to the invention, and

[0044] FIG. 2 shows, in the form of a schematic block diagram, a further advantageous embodiment of a method according to the invention—in particular, using high-pressure electrolysis.

[0045] In the exemplary embodiment of a method according to the invention shown in FIG. 1, a feedstock 1, the predominant proportion of which consists of water, is subjected to electrolysis E. In this case, a raw cathode gas 14, which is low in oxygen and rich in hydrogen, and a raw anode gas 2, which is rich in oxygen and contains hydrogen, are formed.

[0046] The raw anode gas is at least partially subjected to a catalytic conversion C as feedstock 3, wherein an intermediate mixture 4 with depleted hydrogen content compared to the raw anode gas is formed. In the catalytic conversion C, hydrogen, which is contained in the raw anode gas 2 in a certain proportion of, for example, 0.1% to 2%, is converted to water with a part of the oxygen which makes up the main proportion of the raw anode gas 2. This effectively reduces the concentration of the hydrogen downstream of the catalytic conversion C.

[0047] The intermediate mixture 4 leaving the catalytic conversion C is subjected in the exemplary embodiment shown here to a first condensation K1, wherein an intermediate mixture fraction 5, with depleted water content compared to the intermediate mixture 4, and a condensate 6, which is rich in water, are formed. The intermediate mixture fraction 5 is compressed and cooled to an adsorption pressure level. After cooling, the compressed intermediate mixture fraction 5 is subjected to a further condensation K2, wherein a further intermediate mixture fraction 8, again with depleted water content compared to the intermediate mixture fraction 5, and a further condensate 9 are formed. The condensates 6, 9 are at least partially returned to the electrolysis E together with the feedstock 1.

[0048] In the exemplary embodiment shown in FIG. 1, the further intermediate mixture fraction 8 is subjected to a drying T in the form of a temperature swing adsorption (TSA), wherein residual water contained in the dryer feedstock is adsorbed on an adsorbent during an adsorption phase. The oxygen contained in the further intermediate mixture fraction 8 does not adsorb substantially on the adsorbent and is carried over into a gas product 10. During a desorption phase, the outlet is closed in the direction of the gas product 10, and the temperature of the TSA device or drying T is increased by overflowing with warm purge gas or by directly heating the adsorber. As a result, previously adsorbed molecules—in particular, water molecules—are desorbed on the adsorbent and can be carried over to a residual gas 11, 12 with a purge gas (not shown), which is formed, for example, using the product stream 10. If the adsorbent is largely free of adsorbed water and other impurities, the temperature is reduced again, and a further adsorption phase is introduced.

[0049] Several TSA devices are, advantageously, operated in parallel with one another, so that at least one of the several TSA devices is in the adsorption phase at any point in time. This allows a continuous stream of the gas product 10 to be provided.

[0050] In particular, it can be ensured that the predominant part of the adsorbed species has again desorbed by maintaining the elevated temperature over a predetermined time, or by taking a concentration measurement downstream of the TSA device or drying T in the residual gas 11, 12. In the event that a period of time is predetermined, the method can, advantageously, be controlled such that the several TSA devices can be operated alternately in the drying T, while the concentration-dependent control has the advantage that the desorption phase can be measured as required, and is not unnecessarily drawn out. As a result, the efficiency of the overall method can be increased.

[0051] At least a part of the residual gas 12 can, upstream of the catalytic conversion C, be returned to the raw anode gas or the feedstock 3, in order to regulate the temperature increase in the catalytic conversion by lowering the hydrogen concentration. For the same purpose, upstream of the drying T, a part of the further intermediate product fraction 8 can also be returned as control stream 13 to the raw anode gas 2 or the feedstock 3.

[0052] Optionally, a further part of the residual gas 11, downstream of the catalytic conversion C, can be returned to the intermediate mixture 4 (not shown) or to the intermediate mixture fraction 5. As a result, product used as a purge gas can still be returned to the process to increase the process yield, even if it is not used for temperature control in the catalytic conversion C.

[0053] In the exemplary embodiment shown in FIG. 1, a series of sensors is integrated into the plant in order to be able to retrieve information about the status of the individual method steps and to thereby regulate the temperature increase in the catalytic conversion C by configuring the returned streams 12 or 13. For example, hydrogen sensors 15 detect the hydrogen concentration of the various gas streams, such as, for example, of the raw anode gas 2. Of course, hydrogen concentrations can also be detected at other points (not shown)—in particular, in a gas stream downstream of the catalytic conversion C—to quantify the degree of conversion.

[0054] A temperature sensor 16 can additionally detect the temperature in the catalytic conversion. With the aid of this information, the supply of raw anode gas or feedstock 3 to the catalytic conversion C can, advantageously, be reduced or stopped if the temperature rises so much as a result of the catalyzed reaction that there is a risk of catalyst degradation. In the case of such a temperature rise in the catalytic conversion, raw anode gas can temporarily be discharged from the process until the temperature has again stabilized to a level that is acceptable for the process. However, the temperature detected by the temperature sensor 16 can also be used as a control variable for configuring the control current 13.

[0055] An advantageous embodiment of a method according to the invention is shown schematically in FIG. 2. In this exemplary embodiment, the electrolysis E is designed in the form of a high-pressure electrolysis, in which the raw anode gas 2 already occurs at the adsorption pressure level. Advantageously, there is thus no need for the compression downstream of the catalytic conversion C, so that the need for the further condensation K2 is also superfluous. In this case, only one compressor is necessary for the return of the residual gas from the drying T and for the return of a part of the gas stream 8, upstream of the drying, which is used as control stream 17. In order to save on a separate compressor for the control stream 17, the residual gas from the drying T can be returned together with the control stream 17 via a compressor and fed downstream of the compressor according to the temperature control upstream (stream 12) or downstream (stream 11) of the catalytic conversion C. Otherwise, the procedure can be identical to the method that was described with reference to FIG. 1.