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U of I study: synthetic fuels via CO2 conversion and FT not currently economically & environmentally competitive

3 July 2016

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.

Master.img-000
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.

Resources

  • 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

July 3, 2016 in Carbon Capture and Conversion (CCC), Diesel, Emissions, Fuels | Permalink | Comments (15)

Comments

Well there is their first mistake: Any process that starts with the burning of fossil fuels is not going to be "environmentally competitive."

ai_win, you made a stupid mistake. They do not use any energy from fossil fuels. They only use the CO2. CO2 has no energy. Energy input is from electricity and H2. They say: "highly renewable or decarbonized", i.e. the same as most people assume for electric and hydrogen cars. Renewable FT fuel is just another pathway of using renewable/decarbonized electricity AND hydrogen (both are needed as you can see in the block diagram, i.e. you could use some electricity to make H2). Nevertheless, the total WTG efficiency is too low (in my view) and the cost is too high. These are the main findings of the study. Put high cabon tax on fossil fuels and the renewable FT fuel will become more competitive. One could argue that the reduction of WTG CO2 emissions by 75% is substantial.

What this study lacks is a comparison in a WTW perspective with other renewable/decarbonized options, such as EV/PHEV/FCV, where electricity and/or H2 are produce from the same resources. Whereas CO2 reduction (in %) will be high in any of the cases (the energy carriers are, per definition, produced from renewable/decarbonized resources), WTW efficiency is the most important tecnical aspect. Cost is also of finterest in this proposed study, where the system boundaries are widened.

They killed my dream of putting synthetic gasoline in my car at a better price than actual petroleum gasoline. But im still dreaming that someone find a profitable way with a solar plant in the desert of california, mexico or texas.

They do not use any energy from fossil fuels.
I wonder where Peter XX thinks the electricity and hydrogen in the 3rd and 5th blocks comes from?

Also im sure that synthetic fuels contain less toxic wastes in the fuel, it's more pure especially compare to bunker fuels that contain sulphur and some metals like arsenic, lead, and others impurities that end-up into the air.

IMO, you'd be better putting the energy straight into electric cars of whatever flavour (BEV or PHEV).

My point Peter is that they assume we can still afford to get any energy from fossil fuels. Yes, the reduction of WTG CO2 emissions by 75% would be substantial but even we could count on that [They say WTG CO2 emissions vary from 180% (nearly twice) to a reduction of 75%.] it still wouldn't be enough. Given the reports of climate change already happening we need to not just reduce how much CO2 we put in the atmosphere we have to be actively reducing the CO2 that we already put in it.

That's always the best first choice.  It's easy to knock off at least 50% of fuel demand with PHEVs if you've got charging available at all stops, and that cuts the size of the remaining problem in half.

So Poet, where does all the electricity come from?

The same electricity that would be used to make the fuels.
Ideally, it would be from a low carbon source like wind, solar, hydro or nuclear.

It would easier to get rid of coal and replace it with anything, (even gas) than burning coal and trying to make fuel from the waste CO2.

Fischer-Tropsch is known to be both inefficient and expensive process. The use of CO2, either from power plant exhaust or from the air, is also not cheap.

It would be more efficient and far cheaper to use waste biomass for pyrolysis combined with hydrogenation (addition of H2) all in one step, (aka hydro-pyrolysis) to produce a bio-crude equivalent to petroleum crude oil that can be refined into various hydrocarbon fuels. Look up Purdue University for detail of this process.

Previous estimates placed this bio-fuel from biomass hydro-pyrolysis to be competitive with gasoline at $3.50-$4.00 per gallon. Not yet competitive with current-day gasoline at $2.5 a gallon, but perhaps a Federal Mandate can require gradually increasing percentages of RE in ALL of our energy supplies annually. This will force a gradual growth in RE in our energy supply, that in time, will become cheaper and cheaper due to experience and economy of scale, in order to totally replace fossil fuels in due time.

The Hydrogen here can come from grid-excess Solar and Wind electricity in order to give predictable return for Solar and Wind investors, in order for Solar and Wind to grow and fulfill even over 100% electricity grid penetration. The Hydrogen can also be used directly for FCV's and for home and office heating and home-based Fuel Cells.

where does all the electricity come from?
Nuclear power does a fine job of generating electricity.  It's good for making bulk heat for almost any purpose.  If you use meltdown-proof reactors like the NuScale which are safe enough to locate in the middle of cities, you could light all the lights, run all the industry, charge all the PEVs and provide all the heat and snow removal as well.

It may be better to get CO2 from the oceans rather than the atmosphere. Using a proprietary electrochemical device, Navy researchers were able to pull carbon dioxide from the water, get hydrogen as a byproduct, and then bounce the two gases off each other to manufacture the liquid fuel. The scientists say they can pull about 97 percent of the dissolved carbon dioxide from the water and convert about 60 percent of the extracted gases into liquid hydrocarbons that can be made into fuel at the cost of approximately $3 to $6 per gallon. With an added 25 percent that comes out as methane (another useful fuel) the conversion rate is 85 %.

The oceans (which cover 70% of the world's surface) will then pull down more CO2 to remain in equilibrium.

http://www.altenergy.org/new_energy/seawater-into-jet-fuel.html

I read the paper on that and the process appeared to be very inefficient, converting perhaps 1/3 of its electric input to hydrogen (there are further losses in conversion to other fuels).  However, if the CO2 in excess of what can be converted using the produced hydrogen is instead sequestered, maybe it could be a carbon-negative system.  I'd have to dig into the paper again.

The real problem is that the thermodynamic limit for CO2 extraction of CO2 from the atmosphere is about 20 kJ/mol, while the energy of methane is almost 900 kJ/mol; even a mol of hydrogen is almost 250 kJ.  If your primary goal is to get CO2 out of the atmosphere, generating chemical fuels is an extremely energy-intensive way to go about it.

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