Integration of Molten Carbonate Fuel Cells in Fischer-Tropsch Synthesis
In various aspects, systems and methods are provided for integration of molten carbonate fuel cells with a Fischer-Tropsch synthesis process. The molten carbonate fuel cells can be integrated with a Fischer-Tropsch synthesis process in various manners, including providing synthesis gas for use in producing hydrocarbonaceous carbons. Additionally, integration of molten carbonate fuel cells with a Fischer-Tropsch synthesis process can facilitate further processing of vent streams or secondary product streams generated during the synthesis process.
1 . A method for synthesizing hydrocarbonaceous compounds, 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 inlet of the molten carbonate fuel cell;
generating electricity within the molten carbonate fuel cell;
generating an anode exhaust comprising H 2 , CO, H 2 O, and at least about 20 vol % CO 2 ;
reacting at least a portion of the anode exhaust under effective Fischer-Tropsch conditions in the presence of a shifting Fischer-Tropsch catalyst to produce at least one gaseous product and at least one non-gaseous product, wherein a CO 2 concentration in the at least a portion of the anode exhaust is at least 80% of a CO 2 concentration in the anode exhaust; and
recycling at least a portion of the at least one gaseous product to the cathode inlet.
2 . The method of claim 1 , wherein a ratio of H 2 to CO in the anode exhaust is at least about 2.5:1.
3 . The method of claim 1 , wherein the recycling step comprises:
removing CO 2 from the at least one gaseous product to produce a CO 2 -containing stream and a separated syngas effluent comprising CO 2 , CO, and H 2 , such that the CO 2 -containing stream has a CO 2 content greater than a CO 2 content in the at least one gaseous product; and
recycling at least a portion of the separated syngas effluent to the cathode inlet.
4 . The method of claim 3 , further comprising oxidizing the at least a portion of the separated syngas effluent prior to it being recycled to the cathode inlet.
5 . The method of claim 1 , further comprising compressing the anode exhaust, the at least a portion of the anode exhaust, or a combination thereof prior to the reacting of the at least a portion of the anode exhaust under effective Fischer-Tropsch conditions.
6 . The method of claim 1 , wherein the shifting Fischer-Tropsch catalyst comprises Fe.
7 . The method of claim 1 , further comprising exposing at least a portion of the anode exhaust stream to a water gas shift catalyst to form a shifted anode exhaust, and then removing water and CO 2 from at least a portion of the shifted anode exhaust.
8 . The method of claim 1 , wherein the cathode inlet stream comprises exhaust from a combustion turbine.
9 . The method of claim 1 , wherein the anode exhaust has a ratio of H 2 :CO of at least about 3.0:1.
10 . 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.
11 . 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.
12 . The method of claim 1 , wherein a fuel utilization in the anode is about 50% or less and a CO 2 utilization in a cathode is at least about 60%.
13 . 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.
14 . The method of embodiment 13, wherein performing the endothermic reaction consumes at least about 40% of the waste heat.
15 . 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%.
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 . A method for synthesizing hydrocarbonaceous compounds, the method comprising:
introducing a fuel stream comprising a reformable fuel into the anode of a molten carbonate fuel cell, an internal reforming element associated with a anode, or a combination thereof;
introducing a cathode inlet stream comprising CO 2 and O 2 into a cathode inlet of the molten carbonate fuel cell;
generating electricity within the molten carbonate fuel cell;
generating an anode exhaust comprising H 2 , CO, H 2 O, and at least about 20 vol % CO 2 ; and
reacting at least a portion of the anode exhaust under effective Fischer-Tropsch conditions in the presence of a shifting Fischer-Tropsch catalyst to produce at least one gaseous product and at least one non-gaseous product, wherein a CO 2 concentration in the at least a portion of the anode exhaust is at least 80% of a CO 2 concentration in the anode exhaust,
wherein an amount of the reformable fuel introduced into the anode, the internal reforming element associated with the anode, or the combination thereof, provides a reformable fuel surplus ratio of at least about 1.5.
18 . The method of claim 17 , further comprising recycling at least a portion of the gaseous product to the anode inlet, the cathode inlet, or a combination thereof.
19 . The method of claim 18 , wherein the recycling step comprises:
removing CO 2 from the at least one gaseous product to produce a CO 2 -containing stream and a separated syngas effluent comprising CO 2 , CO, and H 2 ; and
recycling at least a portion of the separated syngas effluent to the anode inlet, the cathode inlet, or a combination thereof.
20 . The method of claim 19 , further comprising oxidizing the at least a portion of the separated syngas effluent prior to the recycling of the separated syngas effluent to the cathode inlet.
21 . The method of claim 18 , wherein the at least one gaseous product comprises a tail gas stream comprising one or more of (i) unreacted H 2 , (ii) unreacted CO, and (iii) C4-hydrocarbonaceous and/or C4-oxygenate compounds.