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Working Paper

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Natural gas powerplants account for 40% of the electricity generation in the United States[1] and 617 million tons of CO2 emissions a year[2]. The largest powerplants with carbon capture technology utilize a post-combustion absorption technology that must treat a large volume of flue gas and compress CO2 to pipeline specifications from near-ambient pressure. The Allam cycle, patented in 2013 by Rodney Allam, uses oxy-combustion and a supercritical CO2 stream as the working fluid to produce high-purity liquid pipeline CO2. While it was developed commercially at a 50-megawatt thermal (MWt) plant in 2018, the economics for a larger, 300 MW plant had not been documented. This project shows that under the current US tax code, the Allam cycle is less economical than the traditional natural gas combined cycle (NGCC) and NGCC with CDR. However, due to the over 99% capture rate, compared to 90% in post-combustion capture, the breakeven credit to traditional NGCC of $112/tonne for the Allam cycle is lower than the NGCC with CDR breakeven credit of $121/tonne. Similarly, for a desired IRR of 15%, the CO2 credit required for the Allam cycle is $163/tonne compared to $188/tonne for the NGCC with CDR. The Allam cycle provides increasingly better financial returns than the NGCC with CDR as the tax credit for sequestration rises. The results of this analysis were produced by first simulating both powerplants in Aspen Plus, and then conducting a discounted cash flow analysis for various scenarios.



Date Posted: 11 May 2021