Integrated power generation and chemical production using fuel cells at a reduced electrical efficiency
In various aspects, systems and methods are provided for operating a molten carbonate fuel cell at conditions that can improve or optimize the combined electrical efficiency and chemical efficiency of the fuel cell. Instead of selecting conventional conditions for maximizing the electrical efficiency of a fuel cell, the operating conditions can allow for output of excess synthesis gas and/or hydrogen in the anode exhaust of the fuel cell. The synthesis gas and/or hydrogen can then be used in a variety of applications, including chemical synthesis processes and collection of hydrogen for use as a fuel.
1. A method for producing electricity, and H 2 or syngas, using a molten carbonate fuel cell having an anode and cathode, the method comprising:
introducing an anode fuel stream comprising a reformable fuel into the anode of the molten carbonate fuel cell, an internal reforming element associated with the anode of the molten carbonate fuel cell, or a combination thereof;
introducing a cathode inlet stream comprising CO 2 and O 2 into the cathode of the molten carbonate fuel cell;
generating electricity within the molten carbonate fuel cell;
generating an anode exhaust from an anode outlet of the molten carbonate fuel cell;
separating from the anode exhaust a H 2 -containing stream, a syngas-containing stream, or a combination thereof,
wherein an electrical efficiency for the molten carbonate fuel cell is between about 10% and about 40% and a total fuel cell efficiency for the molten carbonate fuel cell of at least about 55%.
2. The method of claim 1 , wherein the syngas-containing stream has a molar ratio of H 2 to CO from about 3.0:1 to about 1.0:1.
3. The method of claim 2 , wherein the molar ratio of H 2 to CO is from about 2.5:1 to about 1.5:1.
4. The method of claim 1 , wherein the electrical efficiency for the molten carbonate fuel cell is about 35% or less.
5. The method of claim 1 , wherein the total fuel cell efficiency for the molten carbonate fuel cell is at least about 65%.
6. The method of claim 1 , the method further comprising reforming the reformable fuel, wherein at least about 90% of the reformable fuel introduced into the anode of the molten carbonate fuel cell, the reforming stage associated with the anode of the molten carbonate fuel cell, or a combination thereof is reformed in a single pass through the anode of the molten carbonate fuel cell.
7. The method of claim 1 , wherein a reformable hydrogen content of the reformable fuel introduced into the anode of the molten carbonate fuel cell, the internal reforming element associated with the anode of the molten carbonate fuel cell, or the combination thereof, is at least about 75% greater than the amount of H 2 oxidized in the anode of the molten carbonate fuel cell to generate electricity.
8. The method of claim 1 , wherein the anode fuel stream comprises at least about 10 vol % inert compounds, at least about 10 vol % CO 2 , or a combination thereof.
9. The method of claim 1 , wherein less than 10 vol % of H 2 produced in the anode of the molten carbonate fuel cell in a single pass is directly or indirectly recycled to the anode of the molten carbonate fuel cell or the cathode of the molten carbonate fuel cell.
10. The method of claim 1 , wherein less than 10 vol % of the syngas-containing stream is directly or indirectly recycled to the anode of the molten carbonate fuel cell or the cathode of the molten carbonate fuel cell.
11. The method of claim 1 , wherein less than 10 vol % of the anode exhaust is directly or indirectly recycled to the anode of the molten carbonate fuel cell or the cathode of the molten carbonate fuel cell.
12. The method of claim 1 , wherein no portion of the anode exhaust is directly or indirectly recycled to the anode of the molten carbonate fuel cell, directly or indirectly recycled to the cathode of the molten carbonate fuel cell, or a combination thereof.
13. The method of claim 1 , further comprising separating at least one of CO 2 and H 2 O from one or a combination of i) the anode exhaust, ii) the hydrogen-containing stream, and iii) the syngas-containing stream.
14. The method of claim 1 , wherein the cathode inlet stream comprises about 20 vol % CO 2 or less.
15. The method of claim 1 , wherein the molten carbonate fuel cell is operated at a voltage V A of about 0.67 Volts or less.
16. The method of claim 1 , wherein the anode exhaust has a molar ratio of H 2 to CO of about 1.5:1 to about 10:1.
17. The method of claim 16 , wherein the anode exhaust has a molar ratio of H 2 to CO of at least about 3.0:1.