Process for producing CO from CO2 in a solid oxide electrolysis cell

Patent metadata

Field	Value
Publication number	US-10494728-B2
Application number	US-201314780462-A
Country	US
Kind code	B2
Filing date	Mar 26, 2013
Priority date	Mar 26, 2013
Publication date	Dec 3, 2019
Grant date	Dec 3, 2019

Abstract

The invention concerns a process for producing carbon monoxide (CO) from carbon dioxide (CO2) in a solid oxide electrolysis cell (SOEC) or SOEC stack, wherein CO2 is led to the fuel side of the stack with an applied current and excess oxygen is transported to the oxygen side of the stack, optionally using air or nitrogen to flush the oxygen side, and wherein the product stream from the SOEC, containing CO mixed with CO2, is subjected to a separation process. The process further comprises heating the inlet gas on both the fuel side and the oxygen side by means of separate heating units, so as to supply heat to the SOEC, where the operation temperature of said heating units is at least equal to the operation temperature of the cell stack minus 50° C., preferably at least equal to the operation temperature of the cell stack.

First claim

The invention claimed is:

1. A process for producing carbon monoxide (CO) from carbon dioxide (CO 2 ) in a solid oxide electrolysis cell (SOEC) stack, wherein CO 2 is led to the fuel side of the SOEC with an applied current, and wherein the content of CO in the output from the SOEC stack is 20-80 wt %, said process further comprising:
heating the inlet gas on the fuel side by means of a heating unit, so as to supply heat to the SOEC, wherein the operation temperature of said heating unit is at least the operation temperature of the cell stack minus 50° C., and
heating the inlet gas on the oxygen side by means of a heating unit, so as to supply heat to the SOEC, wherein the operation temperature of said heating unit is at least the operation temperature of the cell stack minus 50° C., wherein:
a suitable operating temperature for the SOEC is maintained with feed effluent heat exchangers incorporated on both the oxygen side and the fuel side of the SOEC,
the carbon dioxide from a separation unit, which still contains some carbon monoxide, is recycled to the fuel side of the SOEC and tied to the CO 2 feed stream upstream from a feed gas purification unit,
a compartment around the SOEC stack is purged with CO 2 , and
a heater is installed to bring the inlet CO 2 gas, utilized as a compartment purge, up to the operating temperature of the SOEC stack or above.

2. The process according to claim 1 , wherein a product stream from the SOEC stack is subjected to a separation process in the separation unit, said separation unit being selected from pressure swing adsorption (PSA), temperature swing adsorption (TSA), membrane separation, cryogenic separation and liquid scrubber technology, such as wash with N-methyl-diethanolamine (MDEA).

3. The process according to claim 2 , wherein the pressure swing adsorption (PSA) unit comprises an adsorption step consisting of two or more adsorption columns, each containing adsorbents with selective adsorption properties towards carbon dioxide.

4. The process according to claim 2 , wherein the pressure swing adsorption (PSA) unit comprises an adsorption step consisting of two or more adsorption columns, each containing adsorbents with selective adsorption properties towards carbon monoxide.

5. The process according to claim 2 , wherein the pressure swing adsorption (PSA) unit comprises at least two adsorption steps, of which the first step comprises two or more adsorption columns, each containing adsorbents with selective adsorption properties towards carbon dioxide, while the second step comprises two or more adsorption columns, each containing adsorbents with selective adsorption properties towards carbon monoxide.

6. The process according to claim 1 , wherein no flushing on the oxygen side is used and feed gas in the form of CO 2 is provided by two individually controlled flows, of which one shares a heat exchanger with the output flow from the fuel side of the stack and the other shares a heat exchanger with the output flow from the oxygen side of the stack.

7. The process according to claim 1 , wherein a cooling-down rate of the system is controlled, and wherein a fast cooling to below 300° C. in less than 24 hours is secured through addition of a cooling medium to the system in case of power failure.

8. The process according to claim 1 , wherein the carbon dioxide from the separation unit, which still contains some carbon monoxide, is recycled to the fuel side of the SOEC.

9. The process according to claim 7 , wherein a compressor is placed between the SOEC stack and the separation unit.

10. The process according to claim 7 , wherein a purge stream is imposed on the recycle stream to avoid a build-up of unwanted inert components, said purge stream being passed to a catalytic oxidizer to oxidize CO to CO 2 or to a thermal oxidizer before reaching the surrounding environment.

11. The process according to claim 1 , wherein the gas coming from the cathode side of the SOEC is quenched to a temperature of about 400-600° C. to avoid metal dusting.

12. The process according to claim 11 , wherein the quench is carried out with an inert gas, such as N 2 , or preferably with CO 2 .

13. The process according to claim 11 , wherein the feed effluent heat exchanger utilizes the heat from a temperature range within 400-600° C. instead of from the SOEC operating temperature in order to mitigate metal dusting.

14. The process according to claim 1 , wherein H 2 S is added to the feed stream to a level between 50 ppb and 2 ppm to suppress carbon formation in the system.

15. The process according to claim 14 , wherein the H 2 S is added to the feed gas immediately downstream from the feed gas purification unit to protect the SOEC stack and the downstream equipment from carbon formation and metal dusting.

16. The process according to claim 14 , wherein the H 2 S is added to the feed gas immediately downstream from the SOEC stack to protect the SOEC stack and the downstream equipment from carbon formation and metal dusting.

17. The process according to claim 1 , wherein a feed gas purification unit utilizing adsorbents based on active carbon, alumina, ZnO, Ni or Cu is added to avoid poisoning of the SOEC.

18. The process according to claim 1 , wherein small amounts of H 2 are added to obtain a system which is not dependent on a recycle stream.

19. The process according to claim 1 , wherein the heater is applied as a radiant heater, which is incorporated in the CO 2 purge gas manifold, simultaneously heating the physical perimeter of the stack and the inlet CO 2 purge gas.

Assignees

• Haldor Topsoe As

Inventors

• Jakobsson Niklas Bengt
• Pedersen Claus Friis
• Hansen John Bøgild

Classifications

• C25B15/02

  Process control or regulation · CPC title

• B01D2253/102

  Carbon · CPC title

• B01D53/047

  Pressure swing adsorption · CPC title

• B01D2259/402

  using two beds · CPC title

• B01D2257/504

  Carbon dioxide · CPC title