Nuclear Ammonia – a sustainable nuclear renaissance’s ‘Killer App’?

The X-15 aircraft used ammonia as one component fuel of its rocket engine.

I’ve long argued on this blog that that fossil fuel replacement this century could, on technical grounds, be achieved via a mix of nuclear fission, renewables and perhaps also fossil fuels with carbon sequestration, with a high degree of electrification; nuclear would probably end up supplying over half of final energy.

A key component of this energy revolution would be to find feasible ways of converting clean electricity (or heat) into a usable liquid fuel, to replace oil. Although biomass will provide for some of this demand, it is unrealistic to expect vast areas of arable land to be turned over to ethanol production, and as such, various synfuels (e.g., hydrogen and hydrogen-nitrogen or hydrogen-carbon derivatives such as ammonia, hydrazine and methanol) will necessarily be required, manufactured using energy inputs to liberate free hydrogen from water, plus atmospheric or concentrated gas streams to provide the other constituent elements (C, N, O). (A useful recent overview of this topic is Forsberg 2009, Is hydrogen the future of nuclear energy?).

The hydrogen used in synfuel production will likely come from either electrolysis at ~30 % electricity-to-hydrogen conversion efficiency, or via direct nuclear (or solar) heat via high-temperature thermochemical water decomposition, catalysed using the hybrid S-I or Cu-Cl cycles, at a 60 % heat-to-hydrogen conversion efficiency (Orhan et al., 2010). The ratio of future (c2100) direct electricity use to the final energy used in synfuel manufacture (via electrolysis and nuclear heat) was estimated to be 0.4 by Eerkens (2006, pg 135), although this figure did not include battery electric vehicles or biofuels.

Okay, enough background from me. What I really want to highlight here is a recent presentation by Darryl Siemer (in collaboration with Kirk Sorenson and Bob Hargraves) at the 8TH Annual NH3 Fuel Conference 19-21Sep11, Portland OR. It’s entitled “Nuclear Ammonia – A Sustainable Nuclear Renaissance’s ‘Killer App‘”. Darryl notes that:

The case it makes for a US nuclear renaissance implemented with LFTRs would apply with equal force to one implemented with S-PRISMs [IFR]. There never will be a “second nuclear era” if we can’t/won’t convince people that it’s got some unique “killer apps”.

Above is an example slide. There were 50 slides presented in his main talk, plus another 64 kept in reserve for questions! You can view the lot here. It is well worth reading carefully through the whole deck — it is packed with useful information. (My only significant critique is the conflation of “uranium” with the once-through fuel cycle — the sustainability advantage of LFTRs/thorium are equally applied to uranium if the spent fuel is recycled in fast reactors).

After presenting at the conference, Darryl told me the the following:

My talk went great – 49 slides in 27 minutes (just two minutes over) followed up by ten minutes of question-answering during the subsequent break. During the 8 years that this conference has been going on, it was only the second talk given about how nuclear power could make it all actually come true… One thing that the audience seemed to appreciate was its explanation of how nuke-powered cement kilns could make the GHG-neutral “CHx”-type synfuels needed for applications (aviation, chainsaws, etc) that ammonia wouldn’t be much good for.

By the way, who is Darryl Siemer? Here is a brief bio: Darryl Siemer, Ph.D., is a retired Idaho National Laboratory “Consulting Scientist” and an expert in virtually all of the technical aspects of radioactive waste management. Dr. Siemer has  76 journal publications in subjects including electronic circuit design, “wet” analytical methods development,   atomic spectrometry, chromatographic instrumentation, cement/concrete formulation,  and  chemical engineering/materials science related to nuclear fuel reprocessing and waste management. He earned his doctorate in chemistry from Montana State University in 1974 and was an assistant professor of chemistry at Marquette University from 1974-1978. Since then he has served as an affiliate/adjunct professor at the University of Umea (Sweden), Pennsylvania State University, the University of Idaho, and Idaho State University.

This is also interesting — a video of a car that runs on ammonia:

It’s not just about ammonia, of course. As another potential vehicle fuel, you can read about the boron car concept in the online chapter on that topic from Prescription for the Planet (by Tom Blees). And for further details on boron, see these articles by Graham R.L. Cowan at the SCGI site. In short, there are some really exciting possibilities for decarbonising the transport sector in addition to stationary electricity, once we have in place the clean electricity and heat sources such as nuclear fission. I hope that these slides and articles help you better grasp that important holistic view.

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  1. I’ve been thinking about the same concept since I read on a book (I think it was $20 Per Gallon by Christopher Steiner) about a guy somewhere way offgrid who was apparently manufacturing ammonia (and pure oxygen) with windpower (I think it was so far offgrid that it would have cost too much to connect). It could certainly be an interesting way to store energy when power generation capacity is high but demand is low (there might be some infra-costs though).

    At the very least, it would remove the necessity to manufacture most of our ammonia from natural gas and other fossil fuels (Ammonia being widely used for fertilizers and other essential stuff we totally depend on to stay alive). Also, it would be a way to store spare generating capacity from nuclear, windfarms and such. Hydrogen is another, but it has its own problems with storage&transport that ammonia doesn’t seem to have.

    The book also mentions that it can be burned as a fuel, even though there is some slight problems/impurities at the moment (maybe because not much r&d has gone into it). One of the big obstacles has been the cheapness of oil, a trend we see changing as peak oil and its associated problems are kicking in.

  2. The bad rap given to another hydride, methane, and derivatives methanol and dimethyl ether may cause some major advantages to be overlooked. The bio-carbon could come from gasified garbage, roadside weeds or perenniel grasses that don’t need plowing or seeding. Sure methane has a global warming potential but if the smell argument works for ammonia it works for carbon synfuels with the addition of odorants like ethanethiol.

    I wonder if nitrogen oxides NOx are created when burning ammonia in engines. The ‘meth’ fuels burn to produce H20 and CO2 which return to the biosphere. A major plus of synthetic methane is that it can be blended with natural gas and biogas, a point made by the Audi car company with their e-gas system. I don’t think any fuel is viable if the production doesn’t have an EROEI of at least 8 and a retail price of say $3 per litre of petrol equivalent or 9c per MJ higher heating value.

  3. The author might be trying to rescue the future for nuclear reactors, but he is doing nothing to rescue the greenhouse.

    For one thing, ammonia is not “green”. Fugitive ammonia is a worse greenhouse gas than fugitive methane. There are several oxidation products, each of which greys out different parts of the infrared spectrum. One of them, N2O, has a global warming potential 300 times that of CO2 on the 100 year timescale.

    His other claim, that ammonia is “cheap” is questionable. The process of combining hydrogen with nitrogen is exothermic, so a decent proportion of the energy you put into making the hydrogen is lost in the creation of ammonia. Efficient use of nuclear heat requires an endothermic process.

    The Haber process earned two Nobel prizes, and its modern catalysts are jealously guarded commercial secrets, so it’s unlikely to be easily converted to solar thermal, either.

  4. Internal combustion is unfortunately an imperfect process. If some ammonia is not combusted it will smell badly around major roads.

    I wonder if methanol isn’t a better idea for a liquid fuel. Also produced in large quantities today. Doesn’t require pressurized tanks. New methanol engines with peak efficiency of 50% have been developed. Methanol can also be efficiently converted to gasoline (lose only about 7% of the energy).

    Personally I prefer we use nuclear to replace baseload coal and gas turbines first. That should keep us busy enough for the next 50 years. We probably can’t spare much nuclear capacity for liquid fuels production. Though there will be more excess nighttime production of electricity that can be used to charge plugin hybrids. That way the plants can keep running at night and we also solve the commuter transport emissions problem.

  5. Aside from smelling really bad at higher concentrations, I recall reading that ammonia is highly toxic to aquatic wildlife. Are there any studies modelling how much ammonia could end up in urban water systems if vehicles were predominantly powered with ammonia, and how much damage this could do? And how would this compare to current pollution from vehicle use?

    And what are the advantages of ammonia over methanol as a fuel? Methanol is more toxic to us humans, but so is petrol.

  6. The safety issues of ammonia as a fuel worry me. Its a nasty poisonous gas. Any leaks or especially ruptures concern me. The various nitrogen oxides are toxic. And I didn’t twig till Roger Clifton pointed it out that they are also potent greenhouse gases. I’ll look through the slide deck, but are these concerns addressed? I’ve always thought dimethyl ether was the best target for a synthetic liquid fuel.

  7. Does someone has a comparison of Ammonia and Gasoline (with its 100+ toxic and carcinogenic additives)? It would be interesting to see, as I have no clue if ammonia is worse for the environment or aquatic life than gasoline and / or diesel we are now using?

    Personally I think that the most/easiest potential lies in energy storage (during low demand) and replacement for natural gas. burning it to drive around is wholly another topic, of which the first question is if we will have the possibility to drive around after meeting the energy needs of tomorrows world with oil in decline, soon to be followed by other fossil fuels, and EROEI-wise much sooner. Driving around in personal 1-2 ton metal armors is a stupid idea with whatever you use to move you around. Other, basic logistics is another matter (shipping, trains, light rail, even trucks & vans where the others wont be possible).

  8. I too think that ammonia would pose a safety issue as a motor fuel used by the general public. A much better use would be as a bottoming cycle at Rankine-cycle electric power plants. NH3 would be used to condense the steam instead of water. The now-gaseous NH3 would spin another turbine and then be condensed by the cooling water. In additon to extracting more energy, the cooling water return temperature to the river/lake would not be as high.

  9. Paul, there is already a cycle using steam with some ammonia in it, called a Kalina cycle. This has some advantages especially for lower temperature where it is more efficient than steam-only turbines. The heat can also be rejected under pressure as opposed to in a vacuum with normal steam turbines. That means compact cheap condensers and no possibility of inleakage from the condenser coolant environmental water (can cause corrosion especially if using seawater cooling).

    Unfortunately ammonia does add costs due to requirements of leak-tightness. This isn’t such a big problem with ordinary steam turbines; water is non-toxic and you can just buy more demineralized water (cheap). So it requires a large power plant to be worthwhile the overhead costs.

    These features make it attractive for a pressurized water reactor (PWR). One could in fact get 10-15% more power from the reactor. I wonder why no one is proposing to use it for a PWR. Even if it leaks into the reactor it doesn’t cause safety problems (ammonia and nitrous oxide gasses are easily removed from the cleanup systems).

  10. The actual amount of electricity required with modern hydrogen electrolysis is is less than 50 kwh per kg.of hydrogen 70% efficient

    Hydrogen can easily and economically be generated and stored at the service station level as ammonia then resold . While it has half the energy density of propane it has similar storage characteristics and can easily be adapted to work with common propane converted vehicles, fuel cells, or mixed with gas/diesel

    This was confirmed by researchers at the Texas Tech University

    Using off peak electricity which is free in Washington state because the of legislatively mandated wind power that only shows up at night and never when you need it, or off peak nuke power give costs of well under buck a gal zero pollution zero CO2. or $2.50 a gal (gasoline eq) at 5 cents a kwh.

    Another alternative is GTL plants like Shell’s new Qatar plant using natural gas to make diesel at $35 a barrel and easily adaptable to nuclear hydrogen/atmospheric CO2 as feedstock.

  11. Aqueous Ammonia (diluted down to 30% with water) is used in all NOx pollution controls, be they for gas, coal or GT plants. It is injected into the combustion path of the fuel after combustion takes place.

    The public will never allow ammonia to be circulating on the streets and possibly ending up in an accident, everyone of which would require immediate evacuation and haz-mat steams deployed. Not good.

    Still, a very interesting article. NNadir has done written on DME as a substitute for diesel fuel. the Chinese are the biggest users of it…creating it from natural gas and coal, unfortunately.

  12. The rationale for ammonia over other synfuels seems to be that no carbon is required. But getting carbon from the air isn’t that energy intensive even with today’s absorbents so I’d have to call it a minor advantage.

    Kirk says the airflow over a wet cooling tower doesn’t contain enough carbon. But his LFTR can be aircooled and that has plenty more airflow. Also the high heat rejection temps mean that the CO2 absorbent can be regenerated at modest system energy cost.

    So I think that things like LNG, LPG, and the alcohols would remain attractive as synfuels compared to ammonia.

  13. Another advantage of CH4 is that 11 million vehicles worldwide already run on it. That’s piston engines but it can also run in turbines and ceramic fuel cells. In the event that it can’t be synthesised cheaply or without fugitive emissions I suggest we burn less natgas in power stations. Thus semitrailers and combine harvesters can still have CNG after 2050 while city slickers use EVs.

  14. If the CH4 is not mined as crudely as it is today but in stead produced in a chemical factory the fugitive emissions can be made very low. But you need good engines that combust all of the methane to reduce those fugitive emissions.

    I’ve designed a simple metal fibre oxidator that can burn any remaining CH4 (and in fact all CxHx) in the exhaust streams of oil storage pipelines and such. It is very small and would easily fit in a car as well. That would take care of the residual CH4 escaping to the atmosphere.

    Solid oxide fuel cells would be great too. More efficient and theoretically no fugitive combustion emissions.

    CNG, LPG and LNG remain interesting as synfuels IMHO. They are what we use today, which helps with commercialization and infrastructure. They’re non-toxic to the environment as well.

  15. Cyril R,

    Personally I prefer we use nuclear to replace baseload coal and gas turbines first. That should keep us busy enough for the next 50 years. We probably can’t spare much nuclear capacity for liquid fuels production. Though there will be more excess nighttime production of electricity that can be used to charge plugin hybrids. That way the plants can keep running at night and we also solve the commuter transport emissions problem.

    I agree. But I want to emphasise, we need to focus on getting low cost nuclear.

    If we have low cost nuclear, electricity will more quickly substitute for gas for heating and for transport (electric vehicles and or liquid fuels produced using low-cost electricity). All the hot water systems we are now converting to gas will be converted back to electricity if we have low-cost, low emissions electricity.

    So the focus needs to be on getting low cost nuclear. That is a topic that BNCers seem to give little attention to. I’d argue, that is the most important issue we should be tackling – what would we need to do to get nuclear at the lowest possible cost in Australia? What policies do we need to implement to achieve it?

  16. Requiring carbon could be a good or bad thing, depending on the source. If there is a serious attempt made to actively extract CO2 from the atmosphere as part of a geoengineering remediation project, using such CO2 as the carbon feedstock for carbon-based synfuel would be better than using coal.

  17. I’ve experimented with burning charcoal in O2 from water electrolysis to get hopefully pure CO2 Contrast that with .04% w/w in air. Flue gas can be ~13% CO2 and I think about 70% N2. If you follow all the synfuel experiments described in Green Car Congress there are other ideas to get concentrated CO2 like supercritical wet oxidation of organic material.

    My impression is that no true liquid or gas synfuel is yet a clear successor to petroleum based fuels. Fuel made from Canadian tar sands should not be described as synthetic when it creates more CO2 than oil. Fuels that require micro-organisms like yeast or algae don’t seem ready yet. Oil and gas had millions of years of slow pressure cooking – a luxury we no longer have. Whatever synfuel emerges it seems likely to need cheap hydrogen input. Methane (with skunk odour) is ready to use in existing vehicles and pipelines and avoids conversion losses. There’s not going to be much jet travel in 50 years.

  18. It seems that most of the comments are concerned with the toxicity of ammonia to people and/or the environment/atmosphere.

    Let’s address people first. While ammonia is indeed “toxic”, it’s also…

    • no more so than are some of the carbonaceous synfuels that folks like us like to talk about (e.g., methanol or DME)l
    • relatively easy to handle/dispense safely (much like LPG (propane/butane) or DME )
    • much less flammable than is the gasoline which most of us are perfectly content to dispense for ourselves (here in the USA, Oregonians are the sole exception)
    • not carcinogenic as are many of the volatile constituents of that same gasoline
    • readily detected (because it smells) at concentrations far lower than those which are toxic
    • readily dissipated if spilled (unlike most of constituents of gasoline and all of those in LPG, the ammonia molecule is lighter than air)

    As far as the environment is concerned, ammonia…

    • is not a green house gas
    • doesn’t create green house gas when “burned” in fuel cells, IC engines, or gas turbines
    • plus any traces of NOx generated when it is burned are quantitatively converted to pure N2 & water vapor by standard automotive type catalytic converters , see..(
    • would be made of water plus the primary component (not a trace impurity) of air, not of some sort of biomass which would have to be produced instead of food (raising/collecting the required amount of biomass wouldn’t be “free”)

    Free access to publications dealing with these & related subjects can be found at and A bit of GOOGLING will dig up lots more.

  19. Ammonia is safer than gasoline in some respects, and more hazardous in others. It needs to be professionally controlled to avoid health hazards.

    Ammonia is pressurized similarly to propane. In an accident scenario, ammonia will not ignite or explode like gasoline. It is lighter than air, so will not accumulate in low spots. It has a distinctive odor that warns people to stay away. If somehow ignited at 650 degrees C, ordinary water can extinguish the flames.

    Vapor concentrations of 500 ppm are dangerous to breath. Much lower concentrations are not cumulatively harmful because humans and mammals process and excrete it via the urea cycle. It is hazardous to aquatic life that does not have this biological system.

    Ammonia is handled safely today. It is the world’s second most common industrial chemical. Farmers inject it into the soil to form fertilizers. Consumers’ future automobiles may require professional, trained technicians to transfer ammonia into vehicle fuel tanks, much as propane tanks are refilled today. [I remember when this was true for gasoline.]

  20. I think we’re heading towards a methane economy. At least in countries which invest heavily into renewable energy, like Germany. There is a large network of natural gas pipelines in Germany. Combined with underground storage, this reservoir holds enough energy to power Germany for months. The idea is to produce the methane synthetically from excess renewable electricity and carbon derived from biomass gasification and then combust it in gas turbines to produce electricity again when wind and solar are not able to fully cover demand. The round trip efficiency of that process is only 36%, but it beats hydrogen because most of the infrastructure is already in place and methane is easier to handle.

    I guess that with cheap, reliable electricity from nuclear power, synthetic methane could be produced even more cheaply. So maybe in fifty years, countries which chose to stick to nuclear may be exporting methane to those who chose to abandon it.

    The good thing about methane is that it can be refined into all kinds of fuels, including methanol and even kerosene. Methane is compatible with most of the technology we use today, ammonia or hydrogen are not.

  21. I’m in Thailand at the moment, and I noticed that many trucks use CNG. They have gas cylinders mounted behind the cabin (you probably wouldn’t be allowed to drive that way in a Western country). They’re using natural gas, which also used for electricity production here. They could just as well run on synthetic methane.

  22. Has the rate of methane leaking from the natural gas network and from combustion engines ever been quantified? I suppose there are significant differences depending on the state of the infrastructure. Good old Drushba from Siberia to Poland is probably going to leak more than the brand new North Stream pipeline …

  23. I have just read the whole PDF cited in the article above. This seems to be another interesting way to do synthetic fuel. While there might be some safety issues, these are less important than the dangers from driving in the first place, as stated by Barry Brook above. And they are irrelevant compared to the dangers of global warming this solution would avoid.

    The authors don’t seem to like renewable energy. However, I have not found anything in that paper that would exclude using some renewable energy source for the ammonia generation whenever supply exceeds demand.

  24. The wholesale price of ammonia is about $500-$600/tonne ($0.60/kg) . I expect the retail price at a bowser would probably be 2x to 3x the wholesale price (given the distribution costs). Let’s assume $1,500 per tonne ($1.50/kg).

    Can someone tell me what would be the fuel cost per km, for comparison with petrol (fuel cost in an efficient car is about $0.10/km (0.65L/100km x $1.50/L))?
    How far would a car run on 1L (0.737 kg)* of ammonia?

    * density of petrol = 0.737 kg/L (at 60F)
    * density of ammonia = 0.823 kg/L (at 25C)

    For interest:
    Energy density (Wh/kg):
    Ammonia = 4,318
    Methanol = 6,400
    Petrol = 12,200
    Diesel = 13,762
    Methane = 15,400
    Fission U235 = 25,000,000,000

    Energy density (Wh/L):
    Ammonia = 4,325
    Methanol = 4,600400
    Petrol = 9,700
    Diesel = 10,942
    Methane = 6,400

  25. CNG as primary transportation fuel is common in various parts of the US, for buses, fleet vehicles, but not at all common for personal transport. NH3 powered alternatives are being proposed for same kind of initial rollout (I think for fleet vehicles, first, not necessarily public transportation). It’s notable that very high efficiencies (approaching 50%?) have been demonstrated to be achievable in internal combustion engines using compression ignition in diesel engines (diesel + CNG or diesel+ammonia, diesel + any number of cousin-counterpart-analogs). As a point of beginning, cost effective alternative energy rollouts that are simple, reliable, rapidly deliverable, and tend to reduce demand for imports of offshore oil are going to be very attractive to nation-states stressed by the extent of their reliance on fossil fuels, particularly imported fossil fuels, for energy (whether for transportation, electricity, or heat).

  26. I don’t think it’s fair to compare synfuels to fossil fuels without a carbon price. The lack of a carbon price is a massive subsidy on fossil fuels, since it shifts the economic cost incurred by the negative externality “climate change” from the producer and consumer to society as a whole.

    Quantifying the economic effects of climate change is an important issue climate scientists, economists and other experts need to work on.

  27. I should probably have asked my previous question more clearly.

    What would be the fuel cost per km using ammonia fuel?

    Assume a car that does 6.7L/100km on petrol (i.e. $0.10/km with petrol at $1.50/L).

  28. Another concern would be the size of the fuel tank needed to get 700 km range in highway driving. The energy density of ammonia is about 1/2 that of petrol, so the fuel tank would need to be twice the volume, which is about what people expect, unless the conversion efficency is higher.

    Can anyone throw any light on this?

  29. Here’s a list of ammonia fatalities and accident in the USA:

    Doesn’t look so bad. 50 deaths in 22 years. Burning fossil fuels kills hundreds of thousands worldwide every year (possibly >1 million lives shortened in fact, using the higher estimates). Even in the US alone 20,000+ people die prematurely each year from air pollution.

    If the energy source is nuclear then you have the best safety. So the question is how clean is burning ammonia.

    I would suggest though that ammonia has major issues with ‘toxic clouds’ in the event of an ammonia storage depot accident, because all of it that spills will evaporate and be carried by the prevailing wind. It is quite a hassle to prove to the regulators that it is safe. Need lots of high quality containment and suppression systems (eg double walled tanks, massive water spray systems). It does cost a bit and is a bother.

    And again I repeat that removing CO2 from the air has modest energy cost especially if the power cycle heat rejection can be used to regenerate the CO2 absorbent (actual fan power for moving that much air is low, most of the energy is required to manufacture and recycle the absorbent).

  30. A good deal of the commentary now seems to be about how methane (natural gas) makes more sense than ammonia.

    Does it?

    Let’s look at the numbers:
    . today’s EIA’s website tells us that total US shale & “dry” nat gas reserves is about 370,000 billion cubic ft
    . the USA currently derives about 39 quads (quadrillion BTU) worth of energy from oil
    . much (2/3rds?) of that oil is imported & therefore incurs the “costs of addiction” described in my slide set
    . 1 cubic ft of methane =1000 BTU

    years worth of “US energy (oil) independence” represented by all of its natural gas reserves =
    370000*1e9*1000/39e15/(2/3) =14.2

    Does this mean that the USA’s citizens & their elected representatives don’t have to worry their pretty little heads about “change” for another 14.1 years?

    (this calc overestimates that time because methane is used for many other things)

    Re ammonia’s “safety issues”, here are two formal analyses:

  31. Methane can also be produced synthetically, like ammonia, with similar efficiency (Sabatier reaction). They are cousins. I think the point was that CNG and LNG are already used for transport so you’ve got a market for syn methane production with nuclear reactors. CNG and LNG engines can also be straightforwardly adapted to be flex fuel, working on gasoline when no methane station is nearby. This is much more difficult with an ammonia engine.

    Methane is not very toxic, and has low explosive range. The darned thing is that it is a greenhouse gas so we really should pay attention to fugitive emissions. If you have a synfuel factory this isn’t much of an issue, but with a drilling rig its almost impossible to prevent leakage. We’ll also need very good computerized combustion engines to prevent too much leakage from the car tailpipe. But I think these challenges are even worse for ammonia since it smells so badly. Internal combustion engines are not perfect things. Throttle them and combustion becomes imperfect, throwing ammonia out the tailpipe. And then it’ll be like Phoebe’s song: “smelly cat, smelly cat…”.

  32. Here’s why my slides pooh-poohed the notion that today’s petroleum-based fuels could be replaced wiith synfuels made with carbon extracted from air.

    It’s based upon the figures/conclusions in a recent (Je2011) APS analysis:

    Here’s a quote from its Executive Summary:

    The physical scale of the air contactor in any DAC (Direct Air Capture) system is a formidable challenge. A typical contactor will capture
    about 20 tons of CO2 per year for each square meter of area through which the air flows. Since a 1000-megawatt
    coal power plant emits about six million metric tons of CO2 per year, a DAC system consisting of structures 10-meters
    high that removes CO2 from the atmosphere as fast as this coal plant emits CO2 would require structures whose total
    length would be about 30 kilometers”.

    Here’s another:

    “:To evaluate a large DAC facility that could conceivably be built today, this report uses a simplified costing
    methodology applied in industry to early-stage projects. The benchmark DAC system is assumed to have a capacity of 1
    MtCO2/yr and to absorb CO2 by passing air over a solution of sodium hydroxide in a counter-current, closed system. The
    sodium hydroxide solution containing sodium carbonate is then cross-reacted with calcium hydroxide to form calcium
    carbonate as a precipitate. The solid calcium carbonate is decomposed in a natural-gas-fueled, oxygen-fired kiln, with
    capture of the released CO2. The capital cost is estimated to be 2.2 billion dollars, a normalized cost of $2200/(tCO2/yr).
    Capital recovery contributes 60% of the $600/tCO2 estimated avoided cost”.

    My calculation
    How much carbon is in the 20 million, 40 gallon bbls/day * 365 day/a of petroleum currently used in the USA?
    If we assume an average SpG of 0.87 and that this petroleum is 83% (12/14.4) carbon by weight, that number works out to 8.01e14 grams C/a
    Which corresponds to 2.94e15 grams (2940 million metric tons) of CO2/a
    Which at this report’s $2.2 billion/MtCO2 scrubber cost estimate, adds up to an up-front capital cost of $6.46 trillion just to collect one of the raw materials going into that sort of fuel

  33. Darryl Siemer writes,

    Here’s why my slides pooh-poohed the notion that today’s petroleum-based fuels could be replaced wiith synfuels made with carbon extracted from air …

    The physical scale of the air contactor in any DAC (Direct Air Capture) system is a formidable challenge. A typical contactor will capture
    about 20 tons of CO2 per year for each square meter of area …

    This same challenge arises with enhanced weathering approach to decarbonating the atmosphere.

    The solution that recommends itself to me is to have a lot of square metres of contact surface through pulverization and dispersal of an alkaline substance such as forsterite or quicklime.

    The forsterite approach is the one to take if you merely want to make a permanent withdrawal of some CO2 from the atmosphere, because there is plenty of forsterite awaiting pulverization.

    The quicklime method is appropriate if you want to first get pure CO2, by pyrolysing calcium carbonate, and make it into gasoline, and then take as much CO2 out of the atmosphere as the gasoline will eventually, when burned, put back.

    The energy cost of such pulverization and dispersal is low enough, and obviously there is enough surface area, that refuting in vitro or in ferro approaches doesn’t really get you anywhere.

  34. The idea that the waste product of energy production be utterly inoffensive in the environment is attractive. After all, nitrogen is already around us at eight tonnes per square metre.

    A potential alternative to ammonia in (dirty) internal combustion engines, is to use an amine polymer in fuel cells. Although ammonia is also eligible fuel for fuel cells, such a successful fuel cell technology may evolve to take a more tractable form of polymerised nitrogen.

  35. darryl siemer.

    Can you point to any links that would show me the comparative fuel cost per km for a given size car running on: petrol, diesel, LPG, CNG, methanol, ammonia?

    The omparison would have to be based on the estimated price of these fuels to the motorist at the bowser. So all the upstream infrastructure and distribution costs need to be included in the price of the fuel.

  36. At today’s ammonia prices (much higher than it was just a couple years ago) gasoline here in the USA is still a bargain. What we need to be thinking about is how our grandkids are going to live if we don’t begin to do something rational to address long-term issues like this one. It’s not today’s prices that “count”- it’s what they will have to pay in order to live as well as we do.

  37. If carbon synfuels are the preferred route it would be best to avoid nitrogen altogether as well as fossil carbon, rather bio-carbon which is ‘in the loop’ above ground. Let solar powered trees and grass suck up atmospheric CO2 over millions of hectares then harvest some organic material later, possibly once-used as paper or food waste.

    Since elemental hydrogen and oxygen (as in oxyfiring charcoal) carry a major energy penalty perhaps they could be avoided as well, for example
    I seem to recall a microwave based approach somewhere then there’s plasma. If all approaches fail our world is going to get a lot smaller without hydrocarbon fuelled transport. Just in case we don’t solve this problem I favour a policy of conserving enough natural gas to get us through to 2050.

  38. darryl siemer,

    Can you tell me the actual figures for fuel cost per km? I want actual figures so I can compare them. Without figures, the discusioon is meaningless. Has anyone looked into the figures and done the comparison I asked for?

  39. A first approximation of energy cost comparisons for petroleum Vs NH3:

    From Peter Lang above:
    Energy density for petroleum = 9700 kWh/l
    Dittom NH3 = 4325 kWh/l
    Ratio = 2.24
    Assume CSIRO guess of a year or two back happens: Petrol retail in Australia at $5/litre.
    If all else is equal – and it won’t be – then NH3 will have to cost less than $2.22/litre at the bowser to achieve energy parity with petroleum.

    Energy parity with $5/litre diesel is even less, at $1.96.

    Factor up or down for your chosen comparison price, eg currently diesel is about $1.50 where I live. NH3 needs to come in below 59 cents per litre to compete with today’s diesel retail price.

    Add to this, the amount of NH3 required to achieve the same range is about a factor of 3.19 (= 13762/4318) larger, assuming similar efficiency of conversion. There goes the back seat or the luggage space.

    Take another view. How high must the carbon tax on diesel be to bring a notional price of $1.50 level with Peter’s notional guess for NH3 of $1.50 per litre?

    The energy available from the two is in the ration of say 3:1.

    Thus, $1.50 per litre of diesel would buy as much energy as 3 litres, i.e. $4.50 worth of NH3.

    Assuming 86% carbon content in diesel, thus 1 litre diesel => 3.15kg CO2)

    To achieve energy cost parity energy cost parity the required carbon tax (or increase in price of diesel by another means) is $3.00 * 1000/3.15 = $952/tonne of carbon.

    Carbon abatement costs way below this have been cited for other pathways, so I guess that NH3 as a transport fuel will be a long time coming, bar exhaustion of the world’s oil reserves sufficient to drive prices to stratospheric levels.

    As somebody pointed out up-thread, if the energy source for production of NH3 is not carbon-free, the whole NH3 operation fails, so that leaves us with the renewables/nuclear discussion for the additional electricity.

    If we don’t very soon get building gigawatts per annum of carbon-free baseload, all this will matter little. Presence of massive carbon free baseload is an absolute prerequisite for any proposal in support of alternative liquid or gaseous transport fuels to be at all meaningful.

    IMHO, it is already too late to prevent serious damage to climate and oceans. We are considering multiple unachievable figleaf solutions as though they are able to compensate for failure to seriously reduce CO2 emissions due to baseload electricity.

    Let’s not forget that it is this same baseload electricity supply that is being asked to power transport by rail and, via fossil fuel replacments, road, sea and air. Any proposal that does not fully account for increasing electricity demand for these purposes is inadequate.

    The best way to drive towards carbon free electricity appears to me to need more than simply minimising the cost of nuclear and renewable power, but also to INCREASE the cost of carbon-intensive power, eg via a tax on CO2-e emissions.

    Such a tax needs not be equivalent to cost of removal of CO2 from air or ocean; however, to be effective it must be at least sufficient to change the comparative costs so that diesel, coal, petrol and gas become more expensive at the bowser than electricity is at the meter.

    The pessimist in me says that I won’t live long enough to see this happen, in Australia or globally. In which case, the climate fight has been lost.

  40. @ darryl siemer, on 6 October 2011 at 9:23 AM

    Agreed. Today’s cost to cost ratio is meaningless without taking into account future costs – and existing external costs which aren’t factored into the current price of petrol (gasoline) use.

  41. @ John Bennets:

    Thousands of kWh per liter?

    3.6 MJ = 1 kWh

    Energy Densities:

    Gasoline: 34.2 MJ/l, or 9.5 kWh/l.
    CNG at 250bar: 9 MJ/l or 2.5 kWh/l
    Methanol: 15.6 MJ/l or 4.33 kWh/l
    Liquid Ammonia: 11.5 MJ/l or 3.19 kWh/l

  42. John and max,

    The energy densities I quoted were “Wh/L” not “kWh/L”

    By the way, the SI unit for litre is “L” not “l”. It was “l” originally, but was changed to “L” in about the late 1970s to avoid confusion with “1″. For example 100l can be confussed with 1001.

    While I’m at it, for out US friends, the SI symbol for hour and hours is “h” not hr not hrs nor HR, nor HRS, etc.

    The SI symbol for seconds is “s” not “sec”.

    Hope no one objects to me sayoing so.

  43. Tom Keen said:

    Agreed. Today’s cost to cost ratio is meaningless without taking into account future costs – and existing external costs which aren’t factored into the current price of petrol (gasoline) use.

    Sorry. Figures are what is needd. It is adjectives that are useless. Avoiding quantifying is what leads to the dsorrt of nonsense we have with advocating renewable energy and objecting to nuclear.

    You can state your assumptions and “no allowance has been maded for damage costs” or some such thing. I am just seeking a simple comparison fuel cost per km for equivalent vehicles. I have no idea wht the comparitive costs are. Are they different by 10% 100%, factor of 10 or 100.

    One of the factorsI don’t know is the efficency of converting the available energy into motion in the internal combustion engine. This must be known if they’ve been running cars and researching sine 1983 or ehmeever it was.

    So, please do not dismiss the question. Someone here must be able to point me to the answer on this.

  44. Correct, Peter and Max, on both scores – kWh and SI units. I graduated and went off designeing before the change to L and worked for a time in CGS units for a European firm, so I am often not formally correct.

    Delete the k and the ratios remain similar. It’s not worth reworking it all. I will wait for future developments before I change my mind on this one.

  45. This is an excellent presentation:

    It shows why we need to deal with the economics of options, not just the technical.

    If we do not deal with the economics of optins we get led down many wrong paths by those who use emotions to make their point rather than hard headed analysis. Examples of this are:

    - ant-nuclear activism

    - pro-renewable energy activism, subsides, mandates, etc

    - carbon tax and ETS

  46. I didn’t know that you couldn’t use l for liter anymore. Good to know.

    One thing we have to remember in this discussion is that in a post fossil fuel economy, every energy carrier which can be replaced by electricity will be replaced by electricity. Overland freight transportation will experience a significant shift from road to rail. Transportation in general will become less reliant on chemical energy carriers, perhaps making it viable to use bio fuels (instead of synfuels) for the remaining applications (mostly aviation and shipping) without too much of an impact on food production.

  47. Max,

    I doubt anyone here is forgetting these points. But the discussion has been about what fuels (or energy carriers) are potentially viable to replace fossil fuels.

    Therefore, it would be helpful to know the relative costs of each to meet a requirement; e.g., cost per km for a standard size car.

    My question was:

    Can you point to any links that would show me the comparative fuel cost per km for a given size car running on: petrol, diesel, LPG, CNG, methanol, ammonia?

    The omparison would have to be based on the estimated price of these fuels to the motorist at the bowser. So all the upstream infrastructure and distribution costs need to be included in the price of the fuel.

    [Thank you JB for your contribution.]

  48. I’m puzzled that you guys are working in litres rather than kilograms. Surely the design range of a new vehicle is limited by the mass of the maximum fuel load? That is, assuming that the fuel is liquid!

    Using the lower heat of combustion, that is, going to gaseous exhaust, the ratio of gasoline at 44.7 MJ/kg to ammonia at 18.6 MJ/kg is 2.4, which does somewhat improve the argument for ammonia.

  49. In terms of creating transport fuel without increasing fossil carbon emission, an option that seems within easy reach is to put nukes in oil refineries.

    An oil refinery throughputs somewhere between 10 and 50 GW of chemical energy, consuming about 20% of its feedstock to create electricity, hydrogen and process heat. And of course, releasing the corresponding quantity of CO2 into the greenhouse.

    The first few gigawatts you put into that scenario would have to be immediately profitable, as they only need to do what nukes are already proven to do, that is, provide baseload electricity and heat.

    Of course the idea of putting a nuke in the heart of an oilman’s temple might meet with a little er, heat. But then the accountants are bound to win, especially when they are minimising a carbon tax liability.

  50. The design range of the vehicle is limited by the size of the fuel tank. Hence a fuel with a high energy density per liter is preferable.

    It’s a trade off. Ideally you want a fuel which has a high density and a high energy content by weight.

  51. Max and Roger C:
    Ever tried to pack a car for a camping holiday with a couple of kids? Ever try to fit an LPG tank to make a car dual fuel? Did you run out of space or did you overload the springs first? My experience has been that volume limits are reached before mass limits almost always, even with a station wagon.

    Hence, volume seems to be more relevant more of the time. Besides which, if mass is a problem, heavy duty springs are a solution. I did this a few years back on a Landcruiser ute converted to a fire truck. GVM went up from 2030 to 2300kg, which allowed a proper water tank to be fitted.

    Run out of volume and you are looking at changing cars. Essentially, it means that a second or third tank must be strapped on somewhere if the volumetric density of the proposed fuel is less than that of petrol/gasolene/diesel.

    In the case of H2, carriage of which I have had a bit of experience, the real issue is not the volume but the inflexible shape, a cylinder with wall thickness of 10 to 25mm, depending on pressure rating. These things are space-wasting brutes. Gas tanks cannot be moulded to fit the available space. They are always cylinders.

    Back to NH3, the wall thickness is perhaps less, but we are still talking about cylinders. Plus heaters. Plus 20% free/vapour space in each cylinder to ensure that venting is not required due to thermal expansion of the contents (See Darryl Siemer, on 6 October 2011 at 2:56 AM – Reference #2). Venting results in both a loss of fuel and therefore a cost, but it is also hazardous and a fire risk. That 20% is not negotiable.

    The same type of discussion can be had about CNG trucks and buses. Their tanks can be located below the floors. Space for these things is at a premium on sedans, into which they will not fit.

    So, I say that space requirements are more significant than mass, especially for small sedans.

    Energy density is very important. This is also true for storage batteries, but that discussion is for another day, because batteries present limitations due to both volumetric density and mass density.

  52. While we are on the subject of mass and space for storage of gas fuels.

    Long range trucks are designed for maximum payload. Every extra tonne of tank and fuel is one tonne less payload. Shorter range trucks and buses are not so limited. That is one reason why CNG buses are common in, for example, Perth, but CNG semitrailers are not found on the highways heading north from Perth to the Pilbara. Besides which, range is less important for short trips than for 3000km round trips for which it is not unusual to see trucks with 1000+ litres of diesel capacity. A similar energy capacity in gas bottles would be bulkier and heavier, thus losing out both ways.

  53. @ Max, on 6 October 2011 at 6:12 PM:

    “…in a post fossil fuel economy, every energy carrier which can be replaced by electricity will be replaced by electricity.”

    I’m not convinced that liquid fuels will run out as suddenly as your statement suggests. I envisage more a drawn-out whimper than a bang. Smarter heads than mine will come up with liquids that, for a price, will keep the existing car fleet on the road, for a price.

    Whether or not electricity will be the only replacement energy carrier remains to be seen. Flywheels? Manufactured gases? Manufactured liquids? Goodness, we might even see PV vehicles for short trips – say commuting: are these powered by photons or electrons? Wind powered shipping? NH3′s time may not have arrived, but it cannot yet be written off over the long term.

    This valuable thread has clarified some issues and raised just as many questions.

  54. I just did a back of the envelope calculation on the potential of synthetic methane as a transportation fuel:

    To produce methane, you need carbon dioxide. Carbon dioxide can be produced via the anaerobic digestion of biomass. If we choose to digest grass, the resulting gas mix will be approximately 54% CH4 and 46% CO2 by volume. So 1000t grass feedstock are turned into 62t CH4 and 146t CO2. With the addition of 27t of H2 from the electrolysis of water, 146t of CO2 are turned into another 53t CH4 and 119t of H20 in the Sabatier process.

    1000t of biomass + H2 from nuclear or renewable electricity produce 115t CH4.

    The amount of primary energy consumed by road transportation every year in Germany is around 614 TWh. This would require ~44 Million tonnes of CH4, produced from 381 Million tonnes of grass and ~10 Million tonnes of nuclear/renewable hydrogen.
    Assuming that 10kg of grass grow annually per square meter, 11% of the total land area of Germany would be required to grow the 381 Million tonnes of grass necessary to produce the methane (CNG) fuel.
    This compares favourably to corn ethanol: If you assume an average of 2,3 kWh of energy per year per square meter for corn ethanol, you would end up having to plant corn on 75% of the area of Germany to get your 614 TWh of primary energy.

    Now this is just a very crude calculation, but it convinced me that synfuels will always beat biofuels, because of land use constraints.

    But it also showed me that a full hydrogen/methane/ammonia economy will never be a reality. Assuming a 70% efficient electrolysis of water, around 57kWh of electricity have to be expended to produce a kg of hydrogen from water. For 10 Million tonnes a year this leads to an electricity requirement of 580 TWh per year, or 993 EPR reactors running round the clock with the sole purpose of producing electricity for the electrolysis of water in order to produce CNG for German cars and trucks. Energetically, it would be better to use the hydrogen directly in fuel cells. Even more efficient would be to not bother producing these synfuels altogether and use battery electric vehicles. Sure, there is a place for chemical energy carriers even in an “electron economy”, but as I said before, their use would be restricted to power heavy machinery, the trucking business (which would lose most of the freight to electric rail anyway), shipping and aviation (which would all become more expensive than they are today). More stuff would probably be produced locally again as well.


    (unless of course there is a serious blunder in my calculations)

  55. Daryl Siemer quoted

    To evaluate a large DAC facility that could conceivably be built today, this report uses a simplified costing methodology applied in industry to early-stage projects. The benchmark DAC system is assumed ….. to absorb CO2 by passing air over a solution of sodium hydroxide …. sodium carbonate is then cross-reacted with calcium hydroxide to form calcium carbonate as a precipitate. The solid calcium carbonate is decomposed in a natural-gas-fueled, oxygen-fired kiln, with
    capture of the released CO2.

    Why use a rough estimate of a complicated process when a detailed study of a much simpler one is available, the ‘green freedom’ proposal
    I think they are being optimistic on costs, but not crazy, and the basic approach of using water droplets in a cooling tower to get a huge contact area at a reasonable price is neat.
    Didn’t we discus this a couple of years back?

  56. @Max, energy requirement for synfuels
    Something looks wrong. 580 Tw-hr / year is (580/8760) = 0.066 Tw-hr/hr continuous, or 66 Gw, which is 46 EPRs if you grant them 90% capacity factor. Large but not impossible. If you electrify short range commuting and long range freight to get the requirements down, it looks quite plausible.
    (Now someone will point out I’ve dropped a zero too)

  57. Max.

    EPRs make 13 TWh per piece. 1.6 GWe x 8760h x 0.92 capacity factor = 13 TWh. 580/13= 45 EPRs.

    This compares to today’s electric demand in Germany of about 630 TWh, you’d need about 48 EPRs to supply it all.

    So basically similar to the electric demand today.

  58. Ah right, of course, I divided the total amount of TWh by 365, which is nonsense … but bear with me, it’s late. ;)

    48 sounds more manageable. But it would come on top of today’s electricity demand. That’s why I think a hydrogen (or synthetic methane) economy is unlikely.

  59. Most personal vehicles will be plug-in hybrids or fully electric. Freight will largely shift to rail. Regional flights will be displaced by an increasing buildup of high speed rail.
    I see a place for synfuels or biofuels in shipping, mining, construction, agriculture, aviation and what remains of long-distance trucking.

  60. Yes agree Max, we’ll need those 45 nuclear plants to power Germany’s normal electric demand first. And then we may find that there is a whole lot of excess nighttime electricity that we can ‘dump’ in plugin hybrids. That effectively takes care of all commuter cars.

    Your idea of biogas CO2 emissions making twice as much CH4 using nuclear is interesting. The efficiency is basically the same as with today’s transport fossil fuel efficiency. That is if we consider electricity to be the imput. By heat it is much worse. And I think we can do much better with a high exergy source such as electricity. Eg plugin hybrids for the time being.

    Leaves ‘big things that go’ to be dealt with. Trucks, ships and planes. Chemical fuel will be needed for these applications. I’m a little worried about this. For example using 11% of Germany’s land area is not very enticing. That’s a huge environmental impact if using new land. Or food versus fuel impact if using existing agricultural land. And that 11% would only be a fraction of total primary energy needs of Germany. Like David Mackay I believe it is so inefficient we shouldn’t consider them. Certain waste products are available for gasification and anaerobic digestion to fuels, but that’s not so much, and those products were made with energy in the first place, so frankly is more of an efficiency improvement than a real energy generator.

  61. 11% is for the entire 614 TWh we presently use. Biogas compares favourably in energy content per tonne of feedstock compared to other biofuels such as ethanol. With the electrification of commutes and most freight transportation, the demand for fuel will decrease, perhaps by 50% or even 75%. Biogas need not be produced solely from grass, agricultural waste products and landfill gas could and would be used as well.
    Germany is 50% agricultural land by the way, 28,3 % of which are green pastures.
    Some of the anaerobic digestion plants could be located near the nuclear reactors used for hydrogen production, so the reactor waste heat could be used to drive the anaerobic digestion and the Sabatier process. That would relieve you of the need of burning a part of your precious gas in the process of producing more gas.

    It’s interesting to see how all of the methods proposed to store large amounts of renewable energy always work much better with baseload nuclear.

  62. This link contains a 6 minute video on synthetic methane—methane-powered
    They say the hydrogen will come from water splitting using excess wind power generated in the North Sea. They hint that the CO2 may be fossil derived since it is not ‘new’, suggesting flue gas not atmospheric capture. They don’t give a cost per kg of synthetic methane but claim that the economics involves finding an application for high wind output combined with the sunk cost of the gas grid. One minute of excess windpower converts to 300km of driving they reckon.

    As I said upthread synthetic methane will struggle unless
    1) it can retail for $3 per litre of petrol equivalent (35 MJ)
    2) the process has an EROEI of at least 8 (c.f. heavy oil, Brazilian ethanol).

  63. Cyrl R

    Leaves ‘big things that go’ to be dealt with. Trucks, ships and planes.

    One option for them is LNG. In 1991 the Australian Energy Research and Development Corporation began a RD&D program with six large B-Double transport trucks running on LNG between Adelaide and Melbourne. I don’t know if it is still running. We also had the coal trucks running between Appin and Wollongong running on LNG that was extracted from the coal ahead of the areas to be mined and then liquefied in a small LNG plant at the mine. We also had large B-double tanker trucks(s?) running on LNG between Alice Springs and the natural gas fields. There were a number of problems that I remember, but all were considered to be fixable. For example, you couldn’t leave them for very long in the open because the LNG would boil off. Also the tanks were double skin with a vacuum between the inner and outer skins to prevent heat being conducted to the LNG inside the tanks. The spacers that kept the inner and outer tanks separated would break on the rough roads that the Alice Springs truck travelled on. Then the inner tank fell down on the outer tank and heat got into the LNG and boiled it off.

    Of course, the LNG tankers already run on the LNG that boils off from their :LNG cargo.

  64. darryl siemer,

    I am guessing that because you havge avoided my question about cost, ammonia must be very much mpore costly than the other options. Perhaps 100 times? Therefore, perhaps a “pie in the sky” idea?

  65. Regarding the 10kg figure, that’s the amount you can get from a well-tended meadow in ideal conditions.
    I suppose in reality most meadows produce 3.5 to 6 kg with three cuts per year… extensively farmed meadows may produce up to 12kg of grass per square meter per year, but they are used exclusively for cattle ranching.

    This is my source:

    They harvested up to 10.6 tonnes per hectare of dry feedstock but other sources speak of up to eight tonnes of dry feedstock from a hectare of meadow …. I suppose corn would be even better.

    But anyway, I’m not an expert. I guess for a thorough analysis it is better to take the more pessimistic numbers.

  66. JB,

    Thank you for the link. I’ll bookmark that one for future use.

    I understand what you are saying. Here is my take on it (not very different you’re your link except your link says “Table 6; A few non SI units”, whereas I know them as “Table 6: Units permitted for use with the SI”. And your link says both “l” and “L” are accepted symbols for litre and mine says only “L” is acceptable.

    I do not have access to the Australian Standard, so I’ve reverted to what I have ready access to. I have the National Standard of Canada
    The International System of Units (SI), and
    Canadian Metric Practice Guide

    These two documents distinguishe between:

    • SI base units (metre, kilogram, second, ampere, kelvin, mole, candela)
    • SI supplementary units (radian, steradian)
    • SI derived units (e.g. cubic metre, radian per second, newton, hertz, pascal)
    • Units permitted with the SI (e.g. litre, minute, hour, day, year, hectare, tonne)

    Canadian Metric Practice Guide, Table 6: Units permitted for use with the SI<, lists “litre” and states the correct symbol for litre is “L”.

    I also remember Australia making the decision to change from “l” to “L” before I left for Canada in 1976.

    The Canadian Metric Practice Guide also says (just for interest):

    2.6 Rules for Writing Unit Symbols and Names

    All SI units have symbols. Abbreviations such as c.c. and
    sq. cm. shall not be used.

    2.6.1 Symbols:

    (a) Shall be printed in upright type, irrespective of the
    typeface used in the accompanying text. “Upright type”
    excludes italic or other sloped type without otherwise
    restricting the typeface;

    (b) Shall be written in lower-case letters, except that the
    first letter is written in upper case when the name of the
    unit is derived from a proper name (see Tables 1 to 5);
    m metre, s second, A ampere, Wb weber
    L litre

    (c) Shall remain unaltered in the plural;

    (d) Shall be written without a final full stop (period),
    except at the end of a sentence;

    (e) Shall be placed after the complete numerical value in
    the expression for a quantity, a space being left between
    the numerical value and the first letter of the symbol.
    321m, not 321m, for 32 lumens

    Note that when the first character of a symbol is not a
    letter, there is no such space. (However, see Clause 2.1 0.5
    for an exception to this rule.)
    32°C, not 32°C

    There is lots more there too about how to use the SI system correctly. Its interesting to read this stuff again. Like you, I had to convert from imperial (and some cgs) to SI.

  67. I shouldn’t add more unit pedantry to this thread, but sometimes it does matter.
    Max wrote

    Regarding the 10kg figure, that’s the amount you can get from a well-tended meadow in ideal conditions …..”They harvested up to 10.6 tonnes per hectare of dry feedstock but other sources speak of up to eight tonnes of dry feedstock from a hectare of meadow” …. .

    A hectare is 100 m X 100 m = 10^4 m^2 = 0.01 km^2, so 10.6 Te/ha is 10,600 kg / 10,000 m^2 = 1.06 kg/m^2, which brings it into line with Darryl’s figures. This is also in line with David Mackay’s figures for the UK, which concluded that you can’t grow enough biomass to supply anything like today’s needs, but you might just manage enough for air transport. Places with low population density can do much better, of course, but not if they are also required to grow food for all the people that can’t grow enough locally.

  68. I checked again, and it looks like I confused dry and fresh (wet) biomass.

    1t of fresh corn produces ~202 cubic meters of biogas (52% CH4)
    1t of fresh grass produces ~172 cubic meters of biogas (54% CH4)

    The yield per hectare is around 48t/ha for corn, and somewhat less for grass.

    48000kg/10000m^2 = 4.8kg/m^2

    in special circumstances it seems to be possible to get a yield of 10kg per square meter of fresh biomass from meadows.

    When I plug this into my spreadsheet for synthetic methane from biogas + nuclear/renewable H2, I calculate that 19% of the land area of Germany would be required to produce 615 TWh of CH4, which covers the demand of road transportation today (614 TWh) – which would decrease dramatically with large-scale electrification anyway.

    It’s still much better than ethanol.

  69. Instead of grass, I would use corn, which yields more gas. Assuming an average yield of 4.8 kg per square meter would result in using 19% of the land for 615 TWh of CH4.

  70. I wouldn’t use corn. People will need it for food directly or indirectly.

    I would use shit. We gotta lot of shit. Shit from cows, shit from chickens, shit from pigs. Shit is one of the best feedstocks for biogas. Its wet and has a high digestible fraction, and new bacteria, plus concentrates the nutrients in the sludge (which is surprisingly un-smelly).

    If your biomass is dry, gasification is probably more efficient than anaerobic digestion. Though there are some new thermophylic bacteria developed that have very high efficiency and throughput.

    The potential figure for EU-27 is about 454 TWh of biogas from waste streams. Using 5% of arable land in EU-27 gets another 250-750 TWh based on 10-30 tons dry matter per hectare. Call it 1000 TWh for Europe. Total primary energy needs are over 20x that for EU-27 (>20,000 TWh). So you can realistically get 2% energy from waste and 2% from agriproducts but that takes 5% of your arable land. that is a big investment in land for such a small fraction of primary energy.

    Frustratingly, all major energy bodies shamelessly use absurd units such as ton oil equivalent; it is suprisingly hard to find good metric sources.

  71. This was very interesting! Thanks for such a great post! Nuclear really can do everything. I was wondering, what would the thermal efficiency be for these energy carriers? The thermal efficiency of the IFR or LFTR is ~50%. So, electric cars would be the best at around ~40%, but they still have made only niche penetrations. If hydrogen is ~30%, what would be the thermal efficiency of ammonia, methanol, boron, or synthetic gasoline and diesel? Does anyone know? For thermochemical hydrogen production, the thermal efficiency would double. Also, what is the thermal efficiency of new cars, hybrids, and diesels? I think it is around ~30%, ~40%, and ~50%, respectively, but it is hard to find solid confirmation.

  72. …what would be the thermal efficiency of ammonia, methanol, boron, or synthetic gasoline and diesel?

    A good approximation is that they all require a heat engine to produce them, so that ten joules of primary heat is converted into three joules of chemical potential energy and seven joules of waste heat, and then, when the fuel is used, the three joule becomes one joule of shaft work and two joules of waste heat. So the overall efficiency, primary heat to driveshaft torque-times-turns, is 0.1.

    Farther upthread someone was complaining that using nitrogen to condense hydrogen is wasteful because it is exothermic, and really good thermochemical fuel production methods have all their steps endothermic. Ideally that might be true, but I don’t know of any actual fuels that can be produced without some exothermic steps. Better to ask they be small exotherms than to ask they not exist at all.

    In the case of hydrogen from, even if a quantum decoheratron could separate steam that has been heated so hot its hydrogens and oxygens are mostly free atoms into one stream of atomic hydrogen and another of atomic oxygen, and cool them separately, the hydrogen would be useless as fuel because as gas it’s not dense enough. It has to be condensed somehow, and spontaneous condensations, like the one with nitrogen, have to be exothermic.

    The exotherm of ammonia production is pleasantly small, about one-seventh of the one the ammonia will later give when burned.

  73. I must concede a point to GRL Cowan above, about the exothermic step in the production of ammonia.

    The ratio of heat derived from burning 17 kg of ammonia at 18.65 MJ/kg to burning 3 kg of hydrogen at 120.97 MJ/kg is 0.874. That is, much as GRLC put it, only 1/8 of the value of the hydrogen has been lost in the making of ammonia.

    On that basis, the production of ammonia is energetically thrifty.

  74. What Graham’s calculations show is that making synfuels is inefficient no matter what synfuel you’re talking about. So it should be the last thing we’d be doing if we wanted to switch effectively to low carbon energy sources.

    This has always been my primary criticism of synfuels – we need the nuclear power plants for more effective things first, such as displacing coal baseload plants.

    If we use the nuclear plant for synfuels we will keep using fossil fuels for electric generation. We sure don’t have excess nuclear power plants to spare.

    Heck, even using the nuclear plant to displace baseload gas fired plants will allow us more transport fuel in CNG and LNG from the natural gas saved, compared to making synfuels.

    Hecker-than-heck, even using the coal saved from displacing coal baseload plants and making fischer-tropsch fuel from the coal saved will get use more transport fuel than using the nuclear plant directly.

    Tres bizarre, that brings us more carbon mitigation than nuclear synfuels.

    [taking cover for the rotten tomatoes to be thrown at me for saying such things ; ) ]

  75. I agree with Cyril R… we are burning natural gas like there is no tomorrow when it will be the last cheap hydrocarbon we can use in high power to weight vehicles and for quick convective heat. When the gas is flowing countries seem to think it will never run out; example Thatcher era Britain and the North Sea reserves. Soon the Brits will get a lot of their gas from Siberia while hoping never to offend Russia the way Ukraine did. Here south eastern Australia is running short of gas even as northern Australia is exporting it to Asia.

    Trinidad and surprisingly Saudi Arabia now want to conserve gas. Meanwhile the US and Australia are burning it as fast as possible. The Bible has a line to the effect ‘thou cannot serve two masters’ yet we want gas to replace both coal and oil. Also to balance intermittent power, heat homes, cook food and make nitrogen fertiliser. I’d like to see a joint paper between AEMO and the Productivity Commission looking at Australia’s gas supply and demand outlook to 2050. I know both the Parliamentary Library and the ACCC have reports out but they omit in-depth analysis.

  76. @Robert Hargeaves said he would be presenting on nuclear ammonia at the upcoming iThEO (energy from thorium) conference.

    Liquid thorium fluoride reactors? It does prompt an intriguing thought. Nuclear reactors which use water as coolant have temperature and pressure optimised to raise steam in the adjacent loop. However, liquid metal or molten salt reactors offer higher temperatures, perhaps better suited to endothermic chemical processing.

    There is an assumption underlying most of the discussions up thread in that hydrogen is necessary for ammonia production, having been previously obtained, expensively via steam-electricity-electrolysis. Similarly, that the ammonia synthesis has been created by steam-electricity-compression.

    There must be a whole world of supercritical (H2O) possibilities arising from MSRs. Without pretending to any expertise in the area, I wonder if there is a supercritical system similar to N2-H2O-Fe , from which we could extract oxygen to obtain a yield of ammonia.

    (Robert, many of us have been given a lot of work by hit-and-run commenters, so one of our flock was vigilant on behalf of all of us, and equally, all of us welcome your further commentary.)

    iThEO Org home
    2011 Conference

  77. I’m wondering about boron production. It has to be efficient to be attractive.

    High purity boron is currently produced for the nuclear and semiconductor industry for use in enrichment, via electrolysis using B4C as a consumable anode.

    Interestingly the current efficiency of this process is about 98%, ie very good.

    I wonder if this is a method to use boron as an energy carrier for ships and such.

    Basically carry boron and carbon as fuel and react them at high temperature to run an external combustion heat engine. B+4C=B4C.

    Then take the B4C ash off in port and send to the electrorefiner as consumable anode to make new boron.

    For the carbon source an initial load could be high purity petroleum coke. Since this is a closed system, no boron or carbon are used up.

    Would this work?

  78. Nuclear oil (clean coal to liquids via nuclear heat) is still in the running.

    I’ve posted a few recent thoughts in this area on an incentive to get the coal industry to want to outlaw the burning of coal to make electricity.

  79. Cheap batteries for electric cars are like cheap solar power plants. Prices today are >3x too high and falling, but there is no reason to expect this trend to continue much longer as the production rate of both is very large already. I expect high prices to make electric cars top out at a market share of 10-20%; the rest will remain ICE powered.

    For an estimate on sustainable syn fuel cost, consider that (as mentioned up-thread), gasoline has an energy content of 34.4 kWh/gallon. For a plant that buys electricity (say from nuclear or wind) for $0.08/kWh, and makes syn fuel at 60% efficiency, it then makes fuel with an energy cost of $4.60/gallon of gas equivalent (gge). For a LWR nuclear plant or for wind, the electrolyzers and chemical equipment may add $1/W to the plant capital cost (i.e. 25% for LWR or 50% for wind farm), for a wholesale cost of $5.73 for nuclear LWR or $6.90 for wind. Gasoline sales is a very low margin business, so a retail price of $7-8/gge is plausible in the LWR nuclear case.

    For a nuclear plant with thermo-chemical H2 cycle, the capital cost and 30% efficiency loss of the electrolyzer is avoided. Also, the cost of the chemical plant is offset by the turbo-machinery and generator that are not required. As a rough approximation, an optimal thermo-chemical cycle has the same efficiency as the electrical conversion efficiency of a cycle at the same temperature (e.g 50-60% for a VHTR reactors at 900C, 40-50% for LFTR at 700C, and 30-40% for IFR at 500C). So $4.36/gge retail (=34.4 kWh * $0.08/kWh *1.1 ammonia conv * 1.2 distribution * 1.2 retail markup) is plausible for nuclear thermo-chemical (i.e. this price makes it a killer app compared to other sustainable syn fuel sources).

    Basically, if a retail gge price is plausible for hydrogen 20 miles from the plant, then that same price is valid for ammonia 200 miles from the plant, because it’s more transportable and the efficiency is the same (the ammonia conversion step, if the waste heat is recycled, uses about the same energy as hydrogen compression).

    If the syn fuel in question allows use in vehicles which are much more efficient than normal gas cars (e.g. hydrogen, ammonia, methanol, or diesel), then the operating cost is similar to or cheaper than that of today’s gasoline vehicles. Note that flex fuel vehicles must use gasoline-friendly compression ratios, therefore, they will have the same poor efficiency as gasoline vehicles.

    Notice that even a small price increase to capture atmospheric CO2 (to densify the syn fuel) would displease consumers. DAC will never be free, so ammonia will always be the cheapest syn fuel from nuclear, solar, or wind.

    As a fossil-based bridge fuel, ammonia is advantageous compared to other syn fuels, in that it is starts out carbon-free, and has a clear path to sustainable sources. It is probably the only politically acceptable coal-based syn fuel. It is not as exciting as a natural gas based syn fuel, since cng is more efficient and almost as dense; but Middle Eastern producers currently have a cost advantage which makes them politically easy to replace as nuclear ammonia plants come on-line.

    Remember also, that syn fuel production is a necessary pre-condition for peak oil. Without it, the market will continue to demand oil, so we will produce it, no matter the cost.

  80. NW surely methane CH4 is the best ‘hydride’ fuel. While a potent GHG, we have a vast gas grid, 11 million NG powered vehicles world wide and it’s nontoxic. A smidgin of CH4 wafts up our noses from our throats. It can be blended from natgas, biogas and synthetic sources. At say $5 per GJ that’s half a cent per MJ. Diesel at say $1.40 per litre (including fuel tax) of 35 MJ is 4c per MJ. If the switchover point for transport fuels is 5c per MJ that’s $50 a GJ which would put gas fired power stations out of business.

    The effect of high oil prices is hard to predict. If they get electric car costs down and there is no recession perhaps people will buy them. It’s not happening so far. Those who need long range could get bifuel vehicles with expensive petrol or diesel as one fuel and CNG the other fuel. Example. It will take a while for CNG filling stations to emerge.

    Car maker Audi claim they can make Sabatier methane from wind power that would otherwise be curtailed

  81. What about ammonium sulphide?
    It is a stable salt with only moderate cooling
    ,(-18 C°) which could be achieved through the heat of evaporation of liquid ammonia it can be solved in.
    Perhaps this part of ammonia used as a coolant can be used as well.
    Anyhow, the main fuel is asolution of 2(NH4)S in liquid ammonia.

    I am ignoring charges:
    2NH4 +O2-> 2N+2H2O -506kJmol^-1
    S-Ion+H20+O2->H2SO4 -561kjmol^-1
    (Almnost certainly i made mistakes. Correct me if you got the time.
    I took the sulphide as in aquatic solution, in lack of better information, and the water first gaseous and then liquid
    Im too lazy now to calculate the gravimetric energy density.)
    The sulphuric acid might neutralize ammonia in case of accident.
    It could be stored on board until given back to the reprocessing plant
    which converts it back to H2S, or used in industry.
    It´s a matter of logistics not to carry it as a dead weight to long.

  82. Ok.
    I was trapped by the thought if sulfur binds three oxygen, that must be pretty exothermic.
    It seems like there are no chemical possibilities noone has thought of yet, and ammonia really is second-best to CO2-emitting fuels.
    Anyway we shouldnt stop research, since our understanding of molecular bonding is incomplete.

  83. I think for various reasons synthetic methane, rather than ammonia will be the fuel of choice. Sunk costs, the possibility of blending it with natural gas and its nontoxicitiy all speak in favour of methane. In addition to using it in CNG/LNG vehicles, it can be converted further into more complex liquid hydrocarbon fuels, like kerosene.

    The CO2 necessary to produce methane will most probably not be drawn directly from the air but come from digested biomass. Biomass digestion produces mostly CH4 and CO2. The CH4 would be fed directly into the gas grid, while the CO2 would be combined with hydrogen to produce yet more CH4.

  84. As an experiment I’ve tried burning charcoal in pure O2 from water electrolysis. Needs more work. If at all possible N2 and H2S should be excluded which is why flue gas and air injected underground coal gasification UCG are not good primary sources of CO2. Clean air at .04% w/w is too dilute.

    The thing that gets me about gas enthusiasts (NG and CSG) they seem to think it is forever. Somehow we can export most of our offshore gas resources as LNG, replace coal fired baseload power stations, make urea fertiliser for an ever growing population, balance wind and solar and use it to replace diesel. It all sounds good. What do we do in the second half of the century when the cheap gas is gone? Gas seems to be regarded as an inorganic magic pudding. Inorganic because it doesn’t make much CO2 when burned and a magic pudding because no matter how much we use there’ll always be more. Wrong on both counts.

  85. Regarding using biomass plus nuclear hydrogen to make methane or other fuels:
    The aviation industry will have priority access to this type of fuel (hydrocarbon synthetics), because everything else is much worse for jets. I don’t see aviation disappearing, because jets really are faster and in some cases cheaper than high speed trains.

    We’ll have enough trouble growing enough biomass just for the jets (even with a 2x? improvement from the nuclear contribution). Any extra land we put to this use reduces the area that we can devote to food production and wildlife.

    On top of that, it is not clear that synthetic methane can beat the price of ammonia. That’s the deal breaker.

  86. Yeah, with the addition of nuclear hydrogen to convert the CO2 produced in anaerobic digesters to methane, the yield doubles.

    I did a back of the envelope calculation (too bad I lost the excel file when my notebook crashed) that Germany could supply all of its transport energy requirements that way, using only 10%-20% of the availible agricultural land, which the environment ministry says is sustainable and doesn’t impact food prices.

    Anyway, it would be unrealistic to think that all transportation would be powered by synthetic methane. Whatever can be electrified will be electrified and in addition to that there will be a substantial shift from non-electric to electric transportation, so the actual methane demand would be far lower than gasoline demand today.

    Biogas seems to be far superior in energy yield per hectare compared to liquid biofuels. It gets even better when combined with hydrogen.

  87. In addition to that hydrocarbon compounds are used in countless products without which life as we know it would be unthinkable. Hence we’ll need to produce carbon-based synthetic liquids even if we don’t use them for transportation.

  88. Realistically, what are the applications for which liquid (or energy dense) fuels are indispensable? The only ones that come to mind are:

    - Long-distance trucking
    - Aviation
    - Small boats (cargo ships could probably work quite nicely with NPPs)
    - Cars that do 200km+ trips on a semi-regular basis

    How can we solve these specific applications? Well, Aviation will probably have to survive on synfuels – nuclear-sourced process heat and electrolysed hydrogen would be a good way of making that less GHG-intensive. Heck, you could source some of the syngas feedstock from plasma arc gasification.

    Boron (As proposed by G.R.L Cowan and promoted by Tom Blees in Prescription) might be a good application for trucking and maybe even small boats, although there might be issues with oxygen generators and marine environments.

    DME synfuel would make a lot of sense as a ‘drop-in’ solution for personal transport and possibly as an interim one for marine and long-distance trucking.

    The biggest question of all however, is how do you get the current industries and end-users to switch over to our cleaner alternatives that have been proposed in the comments here?

  89. How to get industry to change?
    Make it insanely profitable.
    Heat from coal is 8 times cheaper than heat from oil. Make vehicle fuels from carbon-neutral blends of coal + cellulosic biomass.
    Has about 10% more energy than oil, can be distributed in today’s distribution chain and consumed in today’s vehicles.
    The downside would be powering the plasma torches and dealing with what the carbon-capture system captured.

  90. Long-distance trucking will not have a bright future unless cheap, light, very high capacity batteries are developed or synfuels cost about the same as gasoline / diesel today, which I doubt will be the case.

    Aviation will continue to need hydrocarbon fuels. Our entire mature aircraft technology and aviation infrastructure is built around that type of fuel. Hydrogen is not really a viable alternative right now. It is too bulky and too difficult to handle. The result of the aviation sector’s reliance on liquid fuels will probably be that people fly less than they do today. Short-haul flights will lose out to high speed rail and even some transcontinental long-distance services may lose market share to high-speed sleeper trains (the Chinese plan a high-speed connection from Beijing to Moscow and Berlin, on entirely new tracks designed for speeds of up to 350 km/h).

    Small boats could be electrified. I’m skeptical about nuclear freighters. Safety and proliferation concerns will probably preclude the widespread adoption of nuclear propulsion in shipping outside of special niches. Imagine the public outcry if a nuclear freighter were taken over by Somali pirates!
    Large cargo vessels will probably use synthetic methane (LNG)/ammonia or any other suitable synfuel. Computer-controlled kites and sails will see widespread use because the use of such systems reduces fuel consumption. If synfuels are very expensive, we may even witness the return of pure sailing vessels for “slow cargo” and the construction of a large transcontinental railway network in Eurasia.

  91. LNG tanker ships (bubble boats) already use vapour from the cryogenic tanks as fuel. Mine trucks are starting to use LNG
    The tanks appear to be shielded from falling rocks. Allegedly the expansion of the Olympic Dam mine will take 19 billion litres of diesel so LNG is an alternative.

    I think CNG could power farm machinery even if the region has no gas lines. Mother cylinders could be used to refill vehicle sized cylinders. There are going to be accidents and methane leakage but that’s the price for squandering oil.

    On the price point for synfuel it seems possible that petroleum based fuels may not increase in price that much even as they run out. Note how a barrel of oil stays under $120 or so despite a decline in exportable crude since 2005. The lack of a price signal to make the switch is arguably a form of market failure.

  92. The price signal is causing switching on the supply side, as natural gas to diesel (Shell, Qatar), and tar sand mining (Canada) become reliably proffitable and enter the market. Coal-to-liquids, and perhaps some newer coal + gas to liquids processes would also be proffitable at current prices, but the risk associated with building a plant that then might not opperate if oil prices decline is preventing implementation for the moment. Demand side switching requires much higher prices. European fuel costs of ~$2/L ~ $7.50/US gal have not yet provoked a big switch to electric or even plug-in hybrids, just smaller and incrementally more efficient conventional vehicles. Battery cost/performance is still not good enough, even here. The oil price on its own is never going to push this transition.

  93. Max,
    I think for transformation of biomass into methane, partly direct and partly via CO2, you could use plancton from seawater instead of corn or grass grown on agricultural land. This is what actually happens in nature so you would win two times,
    getting usable methane and reduce the input of carbon dioxide and methane into the atmosphere/raising the pH of the oceans.

  94. A recent review of solid-state ammonia synthesis suggests this still has a very long way to go

    paywalled, unfortunately, but the public abstract contains the useful information

    The highest rate reported so far is found to be 1.13 × 10−8 mol s−1 cm−2 at 80 °C with a potential of 2 V using Nafion membrane, SmFe0.7Cu0.1Ni0.2O3 (SFCN), and Ni-Ce0.8Sm0.2O2−δ as solid electrolyte, cathode and anode, respectively

    10^-8 is a lot of zeros in the wrong place. Converting to more sensible units, 1.13E-08 mol/cm2/s is 1.13E-04 mol/m2/s or 0.113 mmol/m2/s
    Ammonia energy content is 317 kJ/mol or 317 J/mmol (Reference in Roger clifton’s post, above), so the power supplied as ammonia is 317 * 0.113 = 36 W/m^2.
    The electrodes used are porous with lots of internal surface area, but it’s still a few watts/g. You would need hundreds of tonnes of expensive rare-earth catalysts to build powerplant-scale facilities. Of course, if a company were working to develop this and made a major improvement, it wouldn’t get published in the open literature and get picked up in the review, but Haber-Bosch isn’t looking too threatened just yet, and ammonia produced by Haber-Bosch and burned in engines is not a great energy carrier, the losses are too high. If you can replace that with solid state synthesis to do electricity + steam + nitrogen –> ammonia + oxygen, and then use the related technology of ammonia fuel cells to reverse the process in the vehicle, the round-trip efficiency will beat anything except batteries, and without range limitations. That realy would be a ‘killer app’, but we’re not there yet.

  95. For the production of synthetic methane, the source of the CO2 will most likely be biological. Growing plants is the most cost-effective way to bind large amounts of atmospheric CO2. Since liquid fuel demand will be much reduced by the time we need synfuels (which is after we have completely decarbonised the electricity sector, land use competition between energy crops, food crops and undeveloped land shouldn’t be a major issue. The best thing would be, however, to tap into oceanic biomass (algae) to get that CO2.

    Renewables may be quite useful for the production of synfuels, since intermittency is not so much an issue here. In some regions, the marginal cost of a kWh wind power (although intermittent) is lower than the marginal cost of a kWh (new) nuclear power.

  96. I agree that bio-carbon is already ‘in the loop’ above ground. This gives rise to arguments whether building timber is a more sequestered form of carbon than say paper pulp which will soon be burned or rot. I tried a Filipino method for making charcoal from grass but it made a smelly mess. The advantage of perennial grasses is that they don’t need trucks and chainsaws to harvest or any replanting. Roadside weeds, food processing waste and gasified garbage are other sources of biocarbon. I’m not confident that commercial algae farming will succeed.

    The converse is of course that coal, oil, gas, kerogen, bitumen and limestone are pre-sequestered carbon that we are returning to the atmosphere after millions of years safely underground. Leaving it all there doesn’t appear to be an option.

    Using excess windpower may have problems we don’t know about yet. I was surprised to learn offshore wind turbines may need diesel generators for black starts after being idled.

  97. In my opinion we should encourage the use of natural gas instead of oil in transportation wherever possible. This would make the switch to synfuel CH4 easier after the electricity sector has been decarbonised. To totally eliminate emissions we’ll have to eventually use carbon which is recycled above ground.

    I’m not talking about using excess wind power. The most economical option would be to use the wind turbines solely to supply power to the electrolyzers. Energy crops such as corn or perennial grasses could be grown on the land between the turbines.

    How much methane/CO2 could we produce from the bio waste produced every year in the US or some other country using anaerobic digestion?

  98. @ Max
    Charles Forsberg has published several papers on using nuclear heat and hydrogen to enhance the energy available from biomass. He thinks you could get enough diesel / kerosene this way for most of US transport demand – 1.3 billion tonnes / year of biomass at 45% carbon giving ~680 million tonnes of diesel, about 12 million barrels/day. Methane would have higher energy content for the same carbon.


    Conference paper

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