Integrated Power Generation Using Molten Carbonate Fuel Cells
In various aspects, systems and methods are provided for integrated operation of molten carbonate fuel cells with turbines for power generation. Instead of selecting the operating conditions of a fuel cell to improve or maximize the electrical efficiency of the fuel cell, an excess of reformable fuel can be passed into the anode of the fuel cell to increase the chemical energy output of the fuel cell. The increased chemical energy output can be used for additional power generation, such as by providing fuel for a hydrogen turbine.
1 . A method for producing electricity, the method comprising:
introducing a fuel stream comprising a reformable fuel into an anode of a molten carbonate fuel cell, an internal reforming element associated with the anode, or a combination thereof;
introducing a cathode inlet stream comprising CO 2 and O 2 into a cathode of the molten carbonate fuel cell;
generating electricity within the molten carbonate fuel cell, the molten carbonate fuel cell being operated at a fuel utilization of about 60% or less;
generating an anode exhaust comprising H 2 , CO, and CO 2 ;
separating, from at least a portion of the anode exhaust, a first H 2 -rich gas stream comprising at least about 80 vol % H 2 ; and
combusting at least a portion of the first H 2 -rich gas stream to produce electricity.
2 . The method of claim 1 , further comprising performing a water gas shift process on the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof.
3 . The method of claim 1 , further comprising separating CO 2 from the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof.
4 . The method of claim 1 , further comprising separating H 2 O from the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof.
5 . The method of claim 1 , wherein the separating step comprises:
performing a water gas shift process on the anode exhaust or at least a portion of the anode exhaust to form a shifted anode exhaust portion; and
separating H 2 O and CO 2 from the shifted anode exhaust portion to form the first H 2 -rich gas stream.
6 . The method of claim 1 , wherein the first H 2 -rich gas stream comprises at least about 90 vol % H 2 .
7 . The method of claim 1 , wherein combusting step comprises generating steam from heat generated by the combustion, and producing electricity from at least a portion of the generated steam.
8 . The method of claim 1 , wherein the combusting step comprises combusting the at least a portion of the first H 2 -rich gas stream in a turbine.
9 . The method of claim 1 , wherein the cathode inlet stream comprises exhaust from combustion of a carbon-containing fuel in a combustion turbine.
10 . The method of claim 9 , wherein the carbon-containing fuel comprises at least 5 vol % of inert gases.
11 . The method of claim 9 , wherein the carbon-containing fuel comprises at least about 10 vol % CO 2 .
12 . The method of claim 9 , wherein the carbon-containing fuel comprises at least about 10 vol % N 2 .
13 . The method of claim 1 , wherein the anode exhaust has a ratio of H 2 :CO of at least about 3.0:1.
14 . The method of claim 1 , further comprising forming a second H 2 -containing stream from the anode exhaust, the at least a portion of the anode exhaust, the first H 2 -rich gas stream, or a combination thereof; and recycling at least a portion of the second H 2 -containing stream to the combustion turbine.
15 . The method of claim 1 , wherein at least about 90 vol % of the reformable fuel is methane.
16 . The method of claim 1 , wherein the molten carbonate fuel cell is operated at a thermal ratio of about 0.25 to about 1.0.
17 . The method of claim 1 , wherein an amount of the reformable fuel introduced into the anode, the internal reforming element associated with the anode, or the combination thereof, is at least about 75% greater than an amount of hydrogen reacted in the molten carbonate fuel cell to generate electricity.
18 . The method of claim 1 , wherein a ratio of net moles of syngas in the anode exhaust to moles of CO 2 in a cathode exhaust is at least about 2.0:1.
19 . The method of claim 1 , wherein a fuel utilization in the anode is about 50% or less and a CO 2 utilization in the cathode is at least about 60%.
20 . The method of claim 1 , wherein the molten carbonate fuel cell is operated to generate electrical power at a current density of at least about 150 mA/cm 2 and at least about 40 mW/cm 2 of waste heat, the method further comprising performing an effective amount of an endothermic reaction to maintain a temperature differential between an anode inlet and an anode outlet of about 100° C. or less.
21 . The method of embodiment 20, wherein performing the endothermic reaction consumes at least about 40% of the waste heat.
22 . The method of claim 1 , 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 is at least about 55%.