Mitigation of NOx in Integrated Power Production
Systems and methods are provided for capturing CO 2 from a combustion source using molten carbonate fuel cells (MCFCs). The fuel cells are operated to have a reduced anode fuel utilization. Optionally, at least a portion of the anode exhaust is recycled for use as a fuel for the combustion source. Optionally, a second portion of the anode exhaust is recycled for use as part of an anode input stream. This can allow for a reduction in the amount of fuel cell area required for separating CO 2 from the combustion source exhaust and/or modifications in how the fuel cells are operated.
1 . A method for producing electricity using a molten carbonate fuel having an anode and a cathode, the method comprising:
introducing a combustion fuel stream and an O 2 -containing stream into a combustion zone;
performing a combustion reaction in the combustion zone to generate a combustion exhaust, the combustion exhaust comprising at least about 20 vppm of NOx;
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 at least a portion of the combustion exhaust into the cathode of the molten carbonate fuel cell, the cathode inlet stream comprising CO 2 , O 2 , and at least about 20 vppm of a nitrogen oxide;
generating a) electricity within the molten carbonate fuel cell, b) an anode exhaust comprising H 2 and CO 2 , and c) a cathode exhaust comprising less than about half of the NO x content of the cathode inlet stream; and
separating at least a portion of the anode exhaust to form a CO 2 -enriched anode exhaust stream having a higher CO 2 content than the anode exhaust and a CO 2 -depleted anode exhaust stream having a lower CO 2 content than the anode exhaust.
2 . The method of claim 1 , wherein the cathode exhaust comprises about 15 vppm or less of NOx.
3 . The method of claim 1 , wherein the cathode inlet stream comprises about 500 vppm or less of NOx.
4 . The method of claim 1 , wherein the combustion exhaust comprises about 10 vol. % or less of CO 2 .
5 . The method of claim 1 , wherein the combustion zone is operated at a temperature of at least about 1200° F.
6 . The method of claim 1 , further comprising recycling at least a portion of the CO 2 -depleted anode exhaust stream to the combustion zone, to the anode of the molten carbonate fuel cell, or a combination thereof.
7 . The method of claim 1 , further comprising exposing the anode exhaust stream to a water gas shift catalyst prior to separating CO 2 from the anode exhaust stream, a H 2 content of the shifted anode exhaust stream being less than a H 2 content of the anode exhaust stream prior to the exposure.
8 . The method of claim 1 , further comprising recycling a combustion exhaust recycle portion from the combustion exhaust to the combustion zone.
9 . The method of claim 1 , wherein the cathode exhaust stream has a CO 2 content of about 2.0 vol % or less.
10 . 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.
11 . The method of claim 1 , wherein the anode exhaust stream comprises H 2 and CO at a ratio of about 3.0:1 to about 10.0:1.
12 . The method of claim 1 , wherein the combustion fuel stream to the combustion zone is hydrocarbonaceous, a ratio of CO 2 in the cathode inlet stream to NOx in the cathode inlet stream being about 100 to about 10,000.
13 . A method for producing electricity, the method comprising:
introducing one or more fuel streams and an O 2 -containing stream into a reaction zone;
performing a combustion reaction in the combustion zone to generate a combustion exhaust, the combustion exhaust comprising at least about 20 vppm of NOx;
introducing an anode fuel stream comprising a reformable fuel into an anode of the molten carbonate fuel cell, an internal reforming element associated with the anode, or a combination thereof;
introducing a cathode inlet stream comprising at least a portion of the combustion exhaust into a cathode of the molten carbonate fuel cell, the cathode inlet stream comprising a nitrogen oxide content of about 20 vppm to about 500 vppm of a nitrogen oxide;
generating electricity within the molten carbonate fuel cell; and
generating an anode exhaust having a nitrogen oxide content that is less than half of the nitrogen oxide content of the cathode inlet stream.
14 . The method of claim 13 , wherein the fuel stream to the combustion zone is hydrocarbonaceous, a ratio of CO 2 in the cathode inlet stream to NOx in the cathode inlet stream being about 100 to about 10,000.