Efficiently Producing Fuels from Waste CO2 and Off-peak Wind or Other Renewable Energy

Updated 8/10/2012

Introduction to WindFuels and CARMA Economics

The Doty Windfuels process will be able to make all the fuels and petrochemicals modern society depends from renewable energy, CO2, and water. As shown in much more detail in a technical paper we presented at the Spring 2012 National meeting of the American Chemical Society, the dominant portion of the capital cost for a Windfuels plant today would be the electrolyzers – everything else will be minor, after development. Even with current prices for electrolyzers and likely off-peak energy wind energy prices, the Windfuels process can still produce carbon-neutral fuels for under $2.50/gal. As scale-up of Windfuels drives the demand for electrolyzers, their prices will steadily drop – probably to under a quarter of current prices within a decade. The problem for investors is that there is currently a cheaper way to make fuels and petrochemicals in high volume – conventional Gas to Liquids (GTL) processes.
For natural gas at $5/mcf (its likely price in the U.S. by 2013), the cost of the methane needed to make a gallon of diesel by a conventional GTL process would be $0.88/gal. In a very large plant, the cost of capital, with 25 year financing, is ~$0.20/gal, and O&M costs will be similar. The problem for environmentalists is that there are is enormous CO2 release from the conventional GTL plant even if the feed is pure methane – and shale gas typically comes out of the ground containing 12-50% CO2, which is just vented. So transport fuels via GTL using shale gas is not environmentally friendly (no matter what the Big Oil companies say).
Enter CARMA.
We have shown that by adding some renewable hydrogen in a novel methane reforming process (called CARMA) it is possible to reduce or eliminate the CO2 byproduct from methane reforming, or even consume CO2 in the process. It depends mostly on the ratio of renewable hydrogen to methane. The greater this ratio, the “greener” the fuels produced.
The immediate response might be, “But the greater the H2/CH4 ratio, the more expensive the fuels.”
Not necessarily. Adding a small amount of hydrogen allows dramatic reduction in coking rates and increases in catalyst lifetime in key portions of the reforming process. It also permits design of processes with higher efficiency. But the greatest benefit comes from the flexibility it affords in input choice. The price of off-peak energy grid energy can easily go from $20/MWhr to sharply negative, and the price of natural gas can change by a factor of three in several years. The CARMA process allows the plant to operate at maximum efficiency over an extremely wide range of input mixes as the markets change.
Over 90% of the input energy could initially come from shale gas, while eventually the input energy could come totally from renewable hydrogen. The amount of CO2 required by the CARMA process increases with the H2/CH4 feed ratio. The table below summarizes costs for several CARMA-GTL scenarios in small commercial plants producing 5 Mgal/yr of fuels. These numbers come from complete plant simulations using advanced process software (Design-II by WinSim) and reaction software (HSC7). The numbers have been validated by experiments and other software.
When the ratio of wind input energy to methane input energy exceeds ~0.5, the capital costs are dominated by the electrolyzer costs, for which we assume (extrapolating from the past decade) a cost of $0.7/W in 2015. The electrolyzer also produces oxygen, some of which is needed for the CARMA process. When the ratio of wind energy to methane energy is above ~0.15, there is excess oxygen, when can be sold. In the table below, revenue from excess oxygen production is used to offset cost of inputs before calculating net costs. In all cases, water usage is insignificant in cost and quantity. Capital costs below assume the 3rd 5-Mgal/yr commercial plant, interest rate of 5%, and 25-year financing.

As seen in the above table, fuels will be produced from a small plant at costs ranging from $0.88-2.50/gal, and usually nearer the low end of this range. Profit from the 5 Mgal/yr plant could easily exceed $10M annually. Larger plants will achieve somewhat higher efficiency, but the primary savings in larger plants will come from reduced capital costs.
Preliminary laboratory experiments have validated crucial questions with respect to kinetics and catalyst performance – lifetime, activity, and selectivity. The detailed plant simulations show that the FTS gas-to-liquids processes can be scaled down with competitive cost and efficiency, achieving ~50% efficiency in a 5 Mgal/yr plant and ~65% efficiency at 30 Mgal/yr.
CARMA is distinguished from most alternatives in that it will be rapidly scalable and immediately competitive with relatively little R&D. Adequate low-cost catalysts are commercially available, though improved performance will be possible with our novel, proprietary catalysts. CARMA will function as a near-term bridging solution to the ultimate Windfuels process, which will use no methane. Our experiments have confirmed that the Reverse Water Gas Shift (RWGS) reaction will permit the reduction of CO2 to CO at efficiency approaching theoretical limits in inexpensive reactors. A proprietary low-cost catalyst we recently tested achieved near theoretical CO2 conversion at rates 50 times higher than seen in most prior RWGS experiments.
The domestic off-peak wind and point-source CO2 resources are sufficient to supply more than the entire current domestic transport fuel demand of 500 million gallons per day. Each year the US emits over 4 gigatons of point-source CO2 (from fossil fuel power plants, ammonia plants, cement factories, etc.) and based on a recent study by NREL there is potential for over 1800 GW of off-peak wind power just in the U.S. wind corridor. The only significant scalability hurdle for Windfuels would be the cost of the electrolyzers during the next decade. As long as natural gas is cheap, the CARMA process will be more competitive, and it too is fully scalable. Hence, CARMA technology will be used in the early plants that will steadily and seamlessly transition from low-carbon to fully carbon-neutral fuels over the coming decade as wind hydrogen becomes more competitive. The internal reactor designs and separation processes are identical between the two processes, so the transition from CARMA to WindFuels will involve little more than modularly adding additional electrolyzers as grid integration needs increase and electrolyzer costs decrease.

Advantages for the novel Windfuels/CARMA-GTL processes include:

1. The synfuels produced are the cheapest alternative.
2. The synfuels do not compete with food or agriculture.
3. The CARMA-GTL fuels are cleaner than GTL synfuels with very high methane feed percentage, cleaner than all other fuels – including biofuels – with as little as 30% renewable hydrogen, and ultimately they will be fully carbon neutral – totally from CO2 and renewable H2.
4. The processes are scalable to the level needed to sustainably meet global transport fuel needs.
5. Windfuels will allow the US to become the world’s largest exporter of clean fuels – forever.
6. The capital costs for the plants in $/bbl/day will be similar to that for conventional GTL plants.
7. The CARMA process yields syngas with the needed H2/CO/(CH4+CO2) ratios over a very wide range of CH4/H2 feed ratios when appropriate CO2/H2O/O2 co-feed ratios are chosen.
8. The synfuels process is based mostly on demonstrated commercial technologies.
9. CARMA eliminates the need for expensive very-high-temperature heating to get the syngas.
10. Windfuels/CARMA-GTL will completely solve the wind integration problem by drawing electrical power when excess is available at low prices.
11. The technology includes a scaling down of conventional GTL processes to enable fuel production from distributed methane and wind sources. It will be efficient and competitive in plants as small as 2 Mgal/year, with average wind power input as low as 1.3 MW.

Traditional thinking assumes very large plants are needed for FT, largely due to the need for pure oxygen (in the syngas process) and due to the complexity of the separations systems. The processes we have designed eliminate these drawbacks. Low-flow-rate packed columns can have performance (split ratios, cost/product, etc.) similar to those of trayed columns with flow rates two to three orders of magnitude larger. These needed columns, phase separators, and recuperators are not commercially available. Hence, we are developing the needed equipment, and it will soon form the basis of major new product lines from Doty Windfuels.

Simplified Windfuels Economics Calculations.
Inputs and Outputs. The last decade of experience with GTL plants shows that capital costs are a minor portion (~$0.20/gal) of the total product cost, even though GTL plants are still being designed and made individually. Relative capital costs should be similar in mass-produced Windfuels plants, so clearly the big economic issues are the costs of the feeds and the value of the products.

The needed CO2 would initially come from commercial sources – ammonia and CO2-rich natural gas. Cement factories, fossil power plants, steel plants, and biofuels refineries are other potential sources. The CO2 could be delivered via the rapidly growing CO2 pipeline network (currently driven mostly by enhanced oil recovery, EOR). There is a large market for CO2. 300 million tons (Mt) have been contracted for enhanced oil recovery (EOR), and the beverage market requires tens of millions of tons/year. Today, the price of 99.5% pure CO2 (beverage quality) delivered through high-pressure pipeline is $30-50/ton, and the CO2 pipeline network is rapidly expanding.
As regulations to reduce CO2 emissions are implemented, competition will drive the price down, as the only option other than selling the CO2 will be to pay to exhaust it or pay to sequester it. It is possible that the pipeline price of CO2 could drop to zero if climate change policy becomes very stringent, since the actual cost to separate and clean CO2 from the exhaust of new power plants could drop below $25/ton within 8 years. Eventually, the CO2 might come from the atmosphere, though with current technology the energy required for separating CO2 from the atmosphere is about 15 times greater than from point sources.
If the cost of the input energy is $15/MWh (it has often been available for much less) and the plant efficiency is 55%, the cost of the input energy in synthesized diesel (37.7 kWh/gal) would be $1/gal. The CO2 (currently ~$40/t for beverage grade) would add ~$0.4/gal, and the amortized plant capital costs are expected to be under $0.75/gal (assuming some reduction in electrolyzer costs). This brings the gross fuel cost to ~$2.15/gal. The liquid oxy¬gen co-product could add an income stream of ~$0.9 per gallon of fuel produced, and subsidies for carbon-neutral fuels could be ~$1/gal. So a rough initial estimate is that the plant could sometimes sell fuels for as little as $0.25/gal and still break even.
Even with no market for oxygen, no credit for climate benefit or grid stabilization, buying CO2 at current market prices, and no utilization of natural gas, Windfuels would usually cost under $2.20/gal.
Windfuels could be competitive with oil trading as low as $55/bbl, depending mostly on (1) the price of off-peak low-carbon grid energy, (2) the cost of electrolyzers, (3) the market for the co-produced liquid oxygen (LOX), and (4) the consideration available (such as a carbon tax) for climate benefit.
It is important to appreciate that there is sufficient point-source CO2 potential in the U.S. (over 4 gigatons per year, Gt/yr) and sufficient wind energy potential (~60 PWh/yr) to synthesize over twice the current U.S. liquid fuel usage (~0.7 Gt/yr) and supply twice its other energy needs (~20 TWh/yr).

The FTS process does not produce one specific chemical. Catalysts and conditions are chosen for a desired product emphasis, and the various products must then be separated. The mixture of products (all carbon neutral and of exceptionally high-purity) would normally include gasoline, jet fuel, diesel, ethanol, methanol, ethylene, propylene, butanol, propanol, hydrogen, cyclohexane, and many other hydrocarbons. The ratios depend on the catalysts and reactor operating conditions (temperature, pressure, H2/CO feed mixture, and residence time).

The Long-term Big Picture.
Chemical processes, unlike agricultural processes (including growing and harvesting of algae) are fully compatible with scale up. To illustrate, the larger demonstrations of photosynthetic algal oil production to date (after two decades of strong support) have been at the scale of a few hundred gallons of fuel per year, and costs thus far have all exceeded $2000/gal. (Non-photosynthetic algae have done much better, but they’re just driving up the price of sugar – like ethanol did to corn. Algae might soon be making fuels from sugar at a price of $15/gal; but with any significant scale up, the price of sugar will go through the roof, and with it the price of the fuels derived from it, whether made by yeast or algae.)

The US market needs a supply of 200 Bgal/yr of sustainable, carbon-neutral fuels. Diverting 40% of U.S. corn production to ethanol to produce under 5% (on an energy basis) of our transportation fuel needs has caused the mean global price of corn to roughly double.

Advocates of cellulosic ethanol (CE) have been saying for the past decade the US can find 1 gigaton of cheap CE feed stocks and produce over 25% of our transport fuel needs from such. But that would be equivalent to over three times the sum of current domestic hay, energy wood, corn-stover, and municipal solid waste production. Co-firing of such feed stocks in coal power plants is seeking twice this amount of new biomass. Co-firing of biomass in coal power plants has a much greater impact per ton on reducing CO2 and other harmful emissions than CE production (co-firing 5-15% biomass with coal also has other beneficial effects, on the nature of the ash produced), and co-firing is more economically sound. Most available cheap biomass will likely be consumed in co-firing.
If diverting 40% of our corn production to ethanol caused its price to double, diverting 70% of our wood, hay, and corn-stover production to energy would be much worse – putting prices in the range of $200-600/ton, depending on quality, location, weather, wildfires, labor wages, and the price of oil. If cellulosic feedstocks are $500/ton, the price of cellulosic ethanol will be $6.50/gal (comparable to gasoline at $9.70/gal). In contrast, the price of Windfuels will only drop as its production scales up, as there are no significant resource constraints.
At this point it seems that an optimistic ultimate projection for CE will be under 1% of U.S. fuel production (the DOE simply doesn’t have the budget to build more capacity than that over the next decade).
More importantly, the operating margins on the WindFuels plants will be much better – the cost of the inputs will be much less per gallon of product, the products will be more valuable, and there will be no waste to deal with.
In order to satisfy currently passed state renewable energy standard (RES) mandates, there will need to be an additional ~300 TWh/yr of renewable energy produced in America within the coming decade. Most of this new renewable generation will come from wind, as no other source is nearly as competitive in most regions of the U.S. As additional turbines are installed, curtailment of wind turbines will increase during off peak demand times unless additional demand comes online as well. The Windfuels and CARMA-GTL processes can use that off-peak power, meaning that less energy is wasted and turbine utilization increases. Curtailment in the US alone is predicted to be 1.5 TWh (1.5x109 kWh) for 2012.
A challenge with wind energy has been getting it from good sites to where and when it is needed. The failure of grid management to overcome this challenge is shown in the continual curtailment of wind power throughout the wind corridor (parts of 16 states in the central US from Texas up through the Dakotas, with a lesser branch reaching east to Ohio – purple, red, and orange on the wind speed map below), which has contributed to a rapid slow-down in the wind industry. Both CARMA-GTL and Windfuels provide rapid response to major changes in grid supply and demand. Thus, windfuels will allow complete stabilization of the grid, even if over 50% of the grid energy comes from wind.

Since WindFuels would solve the grid stability challenges, the best way to increase low-carbon peak grid capacity will be to simply put up more wind farms. The extra, off-peak energy will have a strong market for making carbon-neutral, transportation fuels.

The primary challenge with pure Windfuels is that the prices of electrolyzers have not been dropping as rapidly as was projected by DOE studies. Electrolyzers simply cost too much to allow the electrolyzer market to grow, which has prevented the identified economy-of-scale cost reductions to come to pass. The CARMA-GTL process solves this chicken-and-egg dilemma by reducing electrolyzer requirements by a factor of five or more. Shale gas will steadily become more expensive over the coming decade while the cost of electrolyzers will continue to drop as demand from CARMA-GTL processes drives the electrolyzer industry and leads to economies of scale. It will be easy to add more electrolyzers and reduce gas consumption at the CARMA-GTL plants in response to market changes.
The competitiveness of the proposed processes and the absence of resource constraints means that the U.S. could end oil imports within three decades and at the same time begin building a clean-fuels export industry of even greater magnitude, which will have enormous security and economic benefits.
The U.S. is in a unique position of being able to competitively turn CO2 into fuels at the scale needed to affect the global fuels markets. No other country is similarly blessed with excess clean-energy resources, point-sources of CO2, and the requisite industrial infrastructure. The net positive effect on foreign-trade balance of a market-driven industry of this magnitude could exceed one trillion dollars annually by 2040. Such a positive effect on trade balance could lead to the net creation of 10,000,000 jobs.
The U.S. eventually will likely not compete successfully with Asia in solar panels, batteries, wind turbines, or EVs, but the United States can supply most of the world with carbon-neutral liquid fuels forever.

WindFuels are Forever.
Anthropogenic carbon emissions may soon be a little below what was expected a few years ago – mostly because of increased incentives for improved efficiency. However, the positive feedbacks in the climate (especially from the melting of the Arctic) could offset this progress.
There is still no evidence that hydrogen will ever work in the transportation sector. Compared to WindFuels, there is no emissions advantage and no significant efficiency advantage for hydrogen. There are only huge cost disadvantages.
The public will slowly begin to appreciate that plug-in electric vehicles will not have a significant effect on carbon emissions for at least another three decades and that most biofuels are only 5% to 20% carbon-neutral. As a result, incentives and support for fully carbon-neutral WindFuels will steadily increase. Wind will still be providing most of the energy needed for Windfuels many decades from now, but an increasing fraction may come from advanced nuclear reactors and solar as those industries steadily become more competitive.
We show in our discussion of Scalability why WindFuels will not experience the same type of hyperinflation seen over the past six years in biofuels, tar sands, CTL, nuclear, algae-oil, wood pellets, and shale-oil.
WindFuels will be over 85% carbon neutral, and they are completely sustainable. When the last coal power plants are shut down in ~2090, the needed CO2 could come from biofuels refineries, cement factories, ammonia production, steel mills, and the atmosphere.


1. GN Doty, FD Doty, LL Holte, D McCree and S Shevgoor, “Securing Our Energy Future by Efficiently Recycling CO2 into Transportation Fuels – and Driving the Off-peak Wind Market”, Proc. WindPower 2009, #175, Chicago, 2009.

2. The Off-peak Wind Market

3. See http://wilderness.org/files/Oil-Shale-FS-global-warming.pdf .

4. Elizabeth Kolbert, “Unconventional Crude”, Annals of Ecology, Nov. 12, 2007.

5. FD Doty and S Shevgoor, “Securing our Transportation Future by Using Off-Peak Wind to Recycle CO2 into Fuels”, ES2009-90182, ASME Joint Conferences, San Francisco, 2009. Copyright ©2009 by ASME - used by permission for reference only.

6. FD Doty, “Hydrocarbon and Alcohol Fuels from Variable, Renewable Energy...“, PCT WO 2008/115933,

7. G. Ramachandran, “Program on Technology Innovation: Integrated Generation Technology Options”, EPRI, Technical Update, Nov., 2008.

8. SM Cohen, GT Rochelle, J Fyffe, ME Webber, “The Effect of Fossil Fuel Prices on Flexible CO2 Capture Operation”, ES2009-90308, ASME Joint Conferences, San Francisco, 2009.

9. AP Steynberg and ME Dry, eds. Studies in Surface Science and Catalysis 152, Fischer-Tropsch Technology, Elsevier, 2004.

10. S Phillips, A Aden, J Jechura, and D Dayton, “Thermochemical Ethanol via Indirect Gasification and Mixed Alcohol Synthesis of Lignocellulosic Biomass”, NREL/TP-510-41168, 2007.

11. K Harrison, G Martin, T Ramsden, G Saur, “Renewable Electrolysis Integrated System Development and Testing”, NREL PDP_17_Harrison, 2009, http://www.hydrogen.energy.gov/pdfs/review09/pdp_17_harrison.pdf .

12. FD Doty, “High-Temperature Dual-source Organic Rankine Cycle with Gas Separations”, PCT WO 2009/048479, 2009.

13. FD Doty, “Compact, High-Effectiveness, Gas-to-gas Compound Recuperator with Liquid Intermediary”, PCT WO-09082504.

14. See http://www.acorechina.org/uscp/upload/6-11-2009.pdf, Chinese wind turbine growth.

15. See http://www.rechargenews.com/energy/wind/article180724.ece, Chinese wind turbine prices.

16. See http://www.renewableenergyworld.com/rea/news/article/2009/06/wind-turbine-prices-move-down-says-new-price-index?cmpid=WNL-Wednesday-July1-2009 2009.

17. See http://www.grist.org/article/concentrated-solar-power-goes-mainstream/ , and http://social.csptoday.com/news/gerc-proposes-tarriff-solar-thermal-power , 2009.

18. K Weissermel, HJ Arpe, Industrial Organic Chemistry, 4th ed., Wiley, 2003.

19. HR BioPetroleum, http://www.hrbp.com/PDF/Huntley%20&%20Redalje%202006.pdf

20. Eric Wesoff, http://www.greentechmedia.com/articles/algae-biodiesel-its-33-a-gallon-5652.html 2009.

21. M Voith, “Cellulosic Scale-up”, C&EN 87 (17), pp10-13, Apr 27, 2009.

22. A 600,000 gallon tank was quoted by Brown Minneapolis Tank Company as costing about $420K, or under $0.02/kWhr for jet fuel.







CARMA-GTL and WindFuels will compete when oil is as low as $60/bbl.
The RFTS plant is mostly based on technology already well developed for GTL and other purposes.

CSP has potential in very sunny areas where there is need of peaking power, but its energy currently costs $170/MWhr, compared to under $90/MWhr for natural gas.


Fuel from photosynthetic algae will be contributing less than 0.01% of global liquid fuels by 2020, and it will still cost over $60/gal.


How bad has the grid stability problem become in the last year in areas where a lot of wind has been put up?

Power producers have paid up to $200/MWhr for users to take their excess off-peak grid energy.


There will be no shortage of good CO2 sources, and its producers will eventually be paying to avoid emitting it.


According to the IEA, CTL will be contributing less than 0.5% to global liquid fuels by 2020.
Tar-sands could stop growing by 2020 because of pressure from environmental groups – and competition from WindFuels.
The cost of batteries or CAES is ~$150/kWhr.

The tank-component cost of storing energy in liquid fuels is about $0.02/kWhr.

That’s a factor of 7,000 difference when talking about seasonal energy storage.

The chances of major advances in batteries over the next 5 decades are near zero. We agree with the EIA that pure electric and fuel-cell vehicles will comprise less than 0.2% of the U.S. fleet by 2030.
One of the new markets for LOX from WindFuels plants will be at small GTL plants converting flare gas to liquid fuels at small oil fields.

Clean coal, especially with carbon capture and sequestration (CCS) will exacerbate the grid stability problem because it cannot respond well to changes in demand.

Why hasn’t there been another CAES plant completed in the U.S. since the one in McIntosh AL in 1991?

The answer is simple: low efficiency, very high capital cost, and very few locations where they can possibly work.

An underground steel tank large enough for storing compressed air with the energy content of 30 tons of heating oil (380 MWhr) will cost about $150M.

A steel tank for storing 30 tons of heating oil will cost about $10K.

It’s hard to make up a factor of 15,000 in storage cost.

Peak global natural gas is probably less than 18 years away.


Global peak coal may be only 30 years away.

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