Researchers Propose Hydrogen-Augmented Fischer-Tropsch Processes; More Product, No CO2
15 March 2007
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| One of the possible configurations of the proposed H2CAR process. Click to enlarge. |
Purdue University chemical engineers have proposed a modification to the conventional biomass- or coal-to-liquids Fischer-Tropsch process that could, by their calculations, produce sufficient fuel for the entire US transportation sector.
Their process, however, relies on an abundant supply of hydrogen—between 239 and 276 billion kilograms of hydrogen per year—to produce 13.8 million barrels of synthetics per day. The new approach—which the researchers call a “hybrid hydrogen-carbon process,” (H2CAR)—proposes co-feeding a gasifier with hydrogen from a carbon-free energy source, such as solar or nuclear power, and CO2 recycled from the syngas (hydrogen and carbon monoxide) conversion reactor.
The H2CAR process offers a number of advantages compared to conventional biomass- or coal-to-liquids technologies according to models the team developed:
No CO2 is released to the atmosphere or is required to be sequestered as a result of the chemical processing system. When conventional methods are used to convert biomass or coal to liquid fuels, 60% to 70% of the carbon atoms in the starting materials are lost in the process as carbon dioxide whereas no carbon atoms would be lost using H2CAR.
Approximately 40% of the amount of coal or biomass is needed to deliver the same quantity of liquid fuel. This is advantageous for prolonging the life of the known coal reserves as well as in reducing the land area needed for the bioenergy crop. The land area required to grow the biomass for H2CAR is accordingly less than 40% of that needed by other pathways that solely use biomass to support the entire transportation sector.
Current estimates suggest that an annual US biomass supply of 1.366 billion tons could produce approximately 30% of the United States transportation fuel with conventional processes. The H2CAR process shows the potential to supply the entire United States transportation sector from that quantity of biomass.
The synthesized liquid provides H2 storage in an open loop system. The addition of hydrogen atoms to carbon atoms from coal or biomass provides a high-density method for storage of massive quantities of hydrogen. On a carbon atom basis, the energy content of the liquid fuel is higher than that of coal or biomass.
The process is detailed in an open access research paper appearing online this week in the Proceedings of the National Academy of Sciences.
The researchers explain the rationale of using H2 in the H2CAR process by the significantly higher annualized average solar energy conversion efficiency for hydrogen generation versus that for biomass growth.
| Production of 13.8 Mbpd of synthetic oil by using biomass | ||||||
|---|---|---|---|---|---|---|
| Case | Gasifier efficiency % | Biomass land area million km2 | Req. H2 billion kg/yr km2 | H2 land area thousand km2 | Carbon efficiency % | Energy efficiency % |
| Conventional-I | 50 | 5.30 | 0 | 0 | 26.2 | 29 |
| Conventional-II | 70 | 2.51 | 0 | 0 | 36.7 | 40.6 |
| H2CAR-I | 50 | 1.41 | 276 | 62 | ~100 | 52.7 |
| H2CAR-II | 70 | 0.92 | 239 | 54 | ~100 | 58 |
I’m saying, treat biomass predominantly as a supplier of carbon atoms, not as an energy source.
—Rakesh Agrawal, Purdue University
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| Land-area and H2 requirement for conventional and process using PHEVs as a function of drivable distance traveled per single full charge H2CAR of batteries. Click to enlarge. |
Agrawal argues that the new process also would be more practical than all-electric or hydrogen-powered cars, in part because of the limited storage capacity of batteries and hydrogen storage tanks.
The tremendous convenience provided by the existing infrastructure for delivering and storing today’s fuels is a huge deterrent to introducing technologies that use only batteries or hydrogen alone. A major advantage of our process is that it would enable us to use the current infrastructure and internal combustion engine technology. It is quite attractive for hybrid electric vehicles and plug-in hybrid electric vehicles.
—Rakesh Agrawal
Realizing this requires significant research in two areas: finding ways to produce cheap hydrogen from carbon-free sources and developing a new type of gasifier needed for the process.
The proposed H2CAR-based processes also have a strong impact on the future areas of research. The primary research emphasis needs to be on cost-effective H2 production from a carbon-free energy source such as solar or nuclear. In addition, efficient, low-cost, and easy-to-operate methods are needed for the conversion of biomass through reaction with H2 to a suitable hydrocarbon liquid fuel. In the short term, the same is true for the conversion of coal to liquid. The current conversion route of gasification followed by a H2-CO liquid conversion reaction is quite inefficient, and an alternative efficient hydrogenation process is highly desirable.
In the mean time, until such alternate processes are discovered, the preservation of carbon atoms in the current gasification and H2-CO liquid conversion reaction is essential. A proposed solution in this work is to co-feed H2 and recycle CO2 from the H2-CO liquid conversion reactor to the gasifier. Feasibility and development of such gasifiers especially for biomass will require extensive research.
Purdue has filed a patent for the concept. The approach is in the conceptual stages, and a plan for experimental research is in progress.
Resources:
“Sustainable fuel for the transportation sector”; Rakesh Agrawal; Navneet R. Singh; Fabio H. Ribeiro; W. Nicholas Delgass; PNAS published March 14, 2007, 10.1073/pnas.0609921104
Maybe I'm missing something here, but here's my problem with this story:
This method relies on an abundant supply of hydrogen! Last time I checked, we didn't have that. If we had it, a lot of our problems would be solved - we wouldn't need to make biofuel, we could just burn the hydrogen, which would be more efficient.
Unless you make hydrogen from renewable sources, it will produce lots of CO2 (or nuclear waste). In addition, making hydrogen from renewable sources is less efficient than making electricity. It would be more efficient to just run things on electicity.
Bottom line, I don't see why this story is getting such good press. Saying "we invented this great fuel process! (assuming there's lots of hydrogen available)" is kind of like saying " I just invented a cure for poverty ! (assuming everybody had a job that made a million bucks a year)
Posted by: Karkus | 15 March 2007 at 08:03 AM
OK, sorry for that premature post - I guess I do see the point now, after a more careful reading of the story. They're trying to use this more efficient fuel process because of the limited hydrogen/electricity storage and infrastructure capacity, which limits things like how far cars can travel.
Still, I figure it will take time to demonstrate/scale this up, and by that time battery technology might be far enough along to the majority of cars electric .
Posted by: Karkus | 15 March 2007 at 08:11 AM
You could put a nuke plant near one of these plants assuming it was not in NY or wherever.
However, you might have problems with windmills.
On the other hand, if you found a place that was windy and had a lot of coal / biomass, you might have a solution.
Also, if you developed a good way of large scale H2 generation and fuel cells got cheap, you would be in business. On the other hand, if you could generate carbon based liquid fuels, they would be easier to transport than H2.
Butanol anyone ?
Posted by: mahonj | 15 March 2007 at 08:21 AM
Technologically, you can produce hydrogen using renewables (e.g. PV solar, wind, hydro) but using nuclear looks a lot cheaper. I say "looks" because it's only true if you sharply discount the future cost of permanent waste disposal and decomissioning and you assume there will be no major accidents.
Technologically, you can also produce the syngas required for FT using biomass but it's definitely cheaper to do using coal (as South Africa has done for decades). Provided you add enough hydrogen, you will indeed not be emitting any CO2 at the FT plant. However, you absolutely will do so at the tailpipe of the cars and trucks using this clean-burning but very expensive designer fuel. CTL can never lead to lower emissions of CO2 than transportation fuels based on oil or gas.
Ergo: FT based on biomass + H2 from renewables could prove ecologically sustainable but it would be extremely expensive. FT based on coal + H2 from nuclear would be cheaper in the short term and make various lobbyists and politicians rich and happy. However, in ecological terms it's arguably worse - certainly no better - than the status quo.
That said, neither EV technology nor cellulosic ethanol nor biodiesel from algal oil are ready for prime time, so funding basic research into optimizing FT process yields is a good way to hedge your bets. Just remember to ask "cui bono?", i.e. who stands to gain?
Posted by: Rafael Seidl | 15 March 2007 at 08:45 AM
Great idea. Off peak electricity from already operational nuclear power plants costs nothing, conventional electrolysis will produce not only hydrogen (no matter the low efficiency, uranium is still dirt cheap), but oxygen too for more efficient gasification.
It could be built today. Bonus of biomass versus coal is that biomass is very low in sulfur.
Posted by: Andrey | 15 March 2007 at 08:47 AM
I would agree with this approach once they develop thorium reactors:
http://www.cosmosmagazine.com/node/348
Posted by: Oulisee | 15 March 2007 at 09:25 AM
Carbon from biomass and Hydrogen from renewables. It's hard to argue with that. I'm sure the oil companies would love that idea (and support it with loads of money) because it keeps us on liquid fuels. My only misgiving is that it keeps noisy ICE engines in the city.
Posted by: Neil | 15 March 2007 at 09:28 AM
I agree with Rafael. Coal -> auto fuel pumps naturally sequestered carbon into the atmosphere--not exactly the desired outcome from a GHG perspective.
If you're going to create H2 so you can brew up some hydrocarbons, why not recycle the CO2 from power plant flue gas?
Posted by: Nick | 15 March 2007 at 09:36 AM
We have so many potential routes to both energy independence and CO2 emission mitigation. But I imagine the methods that result in profit for the companies that invest in it will win out.
Posted by: Cervus | 15 March 2007 at 09:44 AM
Seems to be an elegant enough and well thought out process, however, the amount of energy transformations involved is fairly staggering. Solar => Electric => Hydrogen => Liquid => Combustion and the additional cycle for getting the coal or biomass into the process. Makes BEV's running on Solar power seem like a cakewalk!
Posted by: DRD T-bone | 15 March 2007 at 10:10 AM
I did the same thing with GTL about 5 years ago. In fact, I think we included the claim in one of my patents. I have to check. I also have to check to see if we said "carbon-based feedstocks" or we limited it to natural gas. If it was the former, I don't think their patent will be allowed.
Anyway, I had a somewhat different motive for doing it (temperature related), but the CO2 benefit was noted. Basically, the CO2 gets water-gas shifted back to CO. But it does ultimately end up as CO2 in the atmosphere once the fuel is combusted.
Robert Rapier
http://i-r-squared.blogspot.com/
Posted by: Robert Rapier | 15 March 2007 at 10:13 AM
An ..easy.. way to get alot of renewable energy is to park 1 million windmills out in the pacific then shunt all that power through a few type 4 reactors to double the h2 production using the heat of the reactors. The result shiuld be a cubic holty vleep of h2.
Posted by: wintermane | 15 March 2007 at 10:31 AM
I think FT/biomass fuel is the way to go. Every step is already proved. And large volumes are possible. It can be boosted by solar and wind and nuclear - in fact any source of power.
Using the hard-to-handle H2 for FT also avoids the problems of distributing hydrogen to thousands of stations all across the nation. And bypasses the fact that cheap fuel cells are not here yet, nor are ICEs burning H2.
If I remember correctly, pure FT uses coal as the carbon input. So hydrogen plus coal can be used instead of biomass. That would allow production in several places great biomass is not available.
The downside - it can be a messy polluting process with lots of steps and efficiency losses at each one. The net CO2 effect depends highly upon whether fossil fuel is used at any step.
Posted by: K | 15 March 2007 at 12:50 PM
On re-reading the article I see that it is all on paper, no actual fuel production yet. So there could be a serious
flaw in the idea. On the other hand another GCC article says nanotechnology will greatly improve hydrogen production by electrolysis. Maybe some renewable electricity could be used in the fuel and some in PHEV batteries. Whatever happens I think there will be fewer cars on the road.
Posted by: Aussie | 15 March 2007 at 01:25 PM
It's not a new concept, and I am not sure what they hope to patent.
http://heikoheiko.blogspot.com/search?q=hydrogen
http://www.spiegel.de/spiegelspecial/0,1518,427152-4,00.html
Looking at my blog I talk about the possibility of using hydrogen to upgrade biomass in virtually every post mentioning hydrogen.
CHORen, a German BTL company, is also well aware of the fact that hydrogen can be efficiently stored in synthetic fuels.
It's still nice for the concept to get a bit of publicity.
What they fail to mention is that, if you are looking for a source of carbon, rather than energy, you might as well take air.
http://www.energyfromthorium.com/pdf/ORNL-TM-2006-114.pdf
80% of the energy required for hydrocarbon production would be for hydrogen, only 20% for the CO2 extraction step.
Posted by: Heiko Gerhauser | 15 March 2007 at 01:52 PM
I'm with Heiko. Nothing new here--it's the approach I've been advocating for a couple of years now--but nice to see it getting more publicity.
Nick asked "why not recycle CO2 from power plant flue gas"? Indeed. It becomes a rather odd path for CTL, but it does have some advantages. Starting with CO2 scrubbed from flue gas and reverse water-gas shifting with electrolytic hydrogen gives you extremely clean synthesis gas. No expensive clean-up processes to avoid poisoning the catalysts for whatever synthesis process you then chose to run.
Posted by: Roge Arnold | 15 March 2007 at 02:50 PM
Forgot to mention one of the biggest advantages of this approach: load following.
Producing the hydrogen to recycle a power plant's CO2 will take substantially more energy than the power plant produces. However, it can be produced from "as available" renewable energy (albeit at some cost in lower capacity factor for the electrolysis equipment). So it can be looked at as an elaborate way of converting intermittently available solar and wind power to reliable "on demand" dispatched power, with production of liquid hydrocarbons as a side effect.
Posted by: Roge Arnold | 15 March 2007 at 02:59 PM
There's a few problems with this proposal:
It leaves us reliant on inefficient ICE engines.
It removes nuclear/renewable sources from electrical generation (however it does solve some of the intermittentcy problems of renewables).
The processing plants would have to be pretty large, and hence would be centralized, requiring transportation of the biomass over long distances, hurting efficiencies.
It will be much cheaper to use coal than it will be to use biomass.
EP has an interesting and flexible (in that it could be tuned to produce electricity or liguid fuels, or actually remove CO2 from the atmosphere... which the above process can not do) here:
http://www.theoildrum.com/story/2006/11/27/0432/3533
Of course, not all of the technologies are ready for prime time, but they do not all have to be ready to have a strong partial system.
Posted by: bbm | 15 March 2007 at 03:18 PM
BBM,
I don't like Engineer Poet's analysis.
Electricity would be a great vehicle fuel, if battery technology was ready, but it isn't, even with the effective $200 per barrel subsidy available in Europe due to high taxes on petrol and low taxes on electricity, there's virtually no electric vehicles on the market,
and in London with exemption from the congestion charge and free parking subsidies get to absolutely ridiculous levels (thousands of Dollars per barrel) and are still not capable of getting more than a few hundred people to buy electric cars.
Likewise, EP needs a bit of a reality check for fuel cells (be it solid oxide or direct carbon) and algae.
Why on earth are people building pulverised coal fired power stations with 40% efficiency, when they could instead get 80% from direct carbon fuel cells?
Or 50% from burning any odd, contaminated rubbish in solid oxide fuel cells?
These things are all great in theory.
Guess what, if we could raise the yield of corn by a factor 5 and the conversion rate to ethanol by a factor 2 (by say making all the stover fermentable), and cut distillation energy demand by 90% through membrane technology (or use waste heat from nuclear power, geothermal or whatever),
corn ethanol would do nicely to meet all petrol demand and we'd even have plenty to spare for other uses, while devoting less land to corn than at present.
We can all dream you know ..., and just maybe corn can be made to produce starch at algae like yields with zero fertiliser input, who knows,
maybe ultracapacitors will turn out to be such efficient electricity storage that they'll even do for planes ...
But, the fact is that with present technology,
electricity is largely a non option for transportation and corn ethanol compares quite favourably to biodiesel from temperate crops on yield (kWh of liquid fuel per hectare) and cost,
sugar cane ethanol is competitive with petrol, and palm oil derived biodiesel is close (depending on prices on the day, it was cheaper than crude oil for part of 2006).
And BTL is significantly more expensive than first generation biofuels with large upfront capital investment. It really looks quite similar to cellulosic ethanol.
Starting with the same amount of wood (and assuming that any process heat, electricity etc. gets used to power the process rather than exported), it's unclear, with no plants built for either technology at commercial scale, whether cellulosic ethanol or BTL, or a combination of the two, would have a greater conversion efficiency to transportation fuels.
Posted by: Heiko Gerhauser | 16 March 2007 at 02:48 AM
Let me add one more thought.
Hydrogen is already being used for transportation fuels. Primarily, it's used to upgrade heavy oil in hydrocrackers and the like.
Hydrogen could also come from electrolysis of renewable electricity, and it does in a few places, notably Iceland.
But, in the US or Europe, nat gas is used for electricity generation.
1 kWh of nat gas can be turned into 0.7 kWh of H2 or 0.6 kWh of electricity.
0.6 kWh of renewable electricity can displace 1 kWh of natural gas equivalent to 0.7 kWh of hydrogen therefore, or at 70% electrolysis efficiency, they'd yield 0.42 kWh of H2.
It makes economic and environmental sense at the moment to use nat gas as a hydrogen source rather than renewable electricity from wind or PV.
Storage for wind or PV electricity isn't much of an issue yet, there's too little on-line.
At some stage of renewables penetration, widespread hydrogen production via electrolysis might make sense in North America or continental Europe, but we aren't there yet.
Posted by: Heiko Gerhauser | 16 March 2007 at 03:08 AM
It has been well known since the FT process was invented that there is an excess of C vs. H for producing lighter hydrocarbons from coal (just by looking at the stoichiometry of the reaction). So introducing H2 from an external source is sort of an obvious way to increase the C utilization. Of course, reality is never quite that simple, and it's nice that these researchers have looked deeper into it.
I think this kind of approach is perhaps one of the more promising ways to eliminate usage of oil for transportation, but from a CO2 perspective the order of importance and the order in which things should be done is something like
1) Decarbonize electricity production. Solar, wind, nuclear, carbon sequestration.
2) Electrified rail, mass transit, PHEV.
3) H2-boosted liquid fuels from biomass.
Step 2 is crucial before step 3 so that the land area required for biomass is reduced. And of course, step 1 must be before 2 or 3, otherwise there isn't that much benefit from electrification and H2-boosting.
Posted by: jb | 16 March 2007 at 03:29 AM
If the goal is to get the most liquid fuel energy for a given quantity of carbon, then propane may be the fuel of choice for surface vehicle engines (or the range extending engines in PHEVs).
Directly hydrogenating biomass may be preferable to gasification/FT, since the latter has significant thermodynamic losses.
Posted by: Paul Dietz | 17 March 2007 at 07:32 PM
This seems more like a carbon "stretching" scheme. Use hydrogen combined with the carbon. It eventually gets into the atmosphere, but at least it is used as a fuel before it does. If you use biomass, I would say ok.
Posted by: sjc | 23 March 2007 at 05:00 PM