U of I study: synthetic fuels via CO2 conversion and FT not currently economically & environmentally competitive
A study by a team at University of Illinois at Urbana−Champaign has found that, with currently achievable performance levels, synthetic fuels produced via the electrochemical reduction of CO2 and the Fischer-Tropsch (FT) process system are not economically and environmentally competitive with using petroleum-based fuel. A paper detailing the study is published in the ACS journal Energy & Fuels.
In their paper, the team investigated an integrated system that converts CO2 released from fossil fuel-burning power plants to synthetic diesel fuel via a combination of the electrochemical reduction of CO2 to CO and the FT process, which uses CO and H2 from electrolysis) as feedstocks.
|Proposed integrated system for liquid fuel production using CO2 electrolysis coupled with the Fischer−Tropsch process. Li et al. Click to enlarge.|
They used currently achievable performance levels for the system components—electrolyzers and the Fischer−Tropsch process—to compute key metrics, including (i) cost of the synthetic fuel; (ii) well-to-gate CO2 emissions; and (iii) overall energy efficiency.
They used a discounted cash flow analysis method to calculate the cost of diesel fuel using a 500 MW power plant as the CO2 source. Their model takes into account capital expenditures as well as operating costs for the reactors and auxiliaries.
The major findings were:
The final cost varies from $3.80 to $9.20 per gallon in 2010 US dollars depending on the projected level of technology achieved.
The WTG CO2 emissions vary from 180% (nearly twice) to a reduction of 75% compared to that of the business as usual scenario without carbon sequestration.
The well-to-gate energy efficiency varies from 41 to 65%.
However, they noted, that with the right combination of high FT fuel yield and low electricity and hydrogen price, the synthetic fuel system could produce fuels at a cost range similar to the reference year 2014 petroleum-based fuel prices.
With the cost of carbon emissions being appropriately included, this electricity to synthetic fuel pathway will be even more economically competitive. This has important implications for energy security because the CO2-based synthetic fuel can be domestically produced with low carbon electricity. The potential WTG CO2 emission reduction with low carbon grid electricity indicates the potential role electrochemical CO conversion can play in low carbon liquid fuel when the electricity grid is highly renewable or decarbonized.
From an electrolysis perspective, assuming low compromise in current density, reducing cell voltage will yield the most beneficial improvements in this technology. The levelized cost of fuel is more sensitive to the change in cell voltage than the change in current density. Additionally, reductions in cell voltage also result in improved efficiency and reduced WTG CO2 emissions.—Li et al.
Xuping Li, Paul Anderson, Huei-Ru Molly Jhong, Mark Paster, James F. Stubbins, and Paul J. A. Kenis (2016) “Greenhouse Gas Emissions, Energy Efficiency, and Cost of Synthetic Fuel Production Using Electrochemical CO2 Conversion and the Fischer–Tropsch Process,” Energy & Fuels doi: 10.1021/acs.energyfuels.6b00665