Nuclear Ammonia

Published in Fossil Fuels Strategy by on October 29th, 2011

The liquid fluoride thorium reactor (LFTR) has the potential to make electric power cheaper than from coal. Typical costs for electric power bought by US utilities average around 5-6 cents per kilowatt hour generated by coal, hydro, and natural gas sources. Government regulations are requiring utilities to buy solar- and wind-generated power at 20-30 cents/kWh. LFTR’s potential cost advantage of 3 cents/kWh is the economic incentive to stop burning CO2-emitting coal, without economically injurious carbon taxes and politically obscured feed-in tariffs. In this way LFTR can improve both the environment and the economy.

There is an additional way to benefit from LFTR’s inexpensive power — synthesizing liquid fuels to replace petroleum. The world gets 37% of its energy from petroleum, vs 21% from coal. A typical nuclear reactor power plant generates about 1 GW (1000 MW) of electric power. A large refinery produces 40 GW of power in the form of gasoline, diesel, and jet fuel. Liquid petroleum fuels contribute to global warming yet are essential to the global economy. Their high energy density and portability make them attractive energy sources for vehicles such as cars, trucks, trains, ships, and airplanes; these all carry their energy sources with them. We can use more LFTR-sourced power for more high speed electric trains and for more small short-range automobiles; we can use LFTR power plants to propel large ocean-going vessels. But we can’t electrify commercial airliners and trucks because they cannot carry heavy, bulky batteries with them.

Petroleum’s high energy density and a century of engineering experience in its use have made it essential to the US economy, and our thirst for it runs to 260 billion gallons per year, of which we import 65% at a cost of $400 billion per year. Our protective presence in the Persian Gulf is estimated to have cost over $7 trillion.

Hydrogen Dissociation

Hydrogen has been touted as the perfect fuel, burning cleanly and emitting only water vapor into the atmosphere after combustion. Hydrogen can be efficiently produced by high-temperature catalytic dissociation or high-temperature electrolysis, possible with advanced nuclear power technologies such as the high-temperature gas cooled reactor (NGNP) favored by Idaho National Labs, or LFTR with molten-salt coolant. The efficiency of conversion from thermal energy to chemical potential energy can approach 50% with the sulfur-iodine cycle if the molten salt temperature is 900 C; a slightly less efficient copper-chlorine cycle can be used at lower temperatures compatible with current nuclear-grade materials.

However hydrogen is an impractical vehicle fuel. To contain it requires either costly refrigeration at -423 F or costly compression to 5000 psi. The small molecules of H2 leak and can embrittle metals.

Energy Density

Nitrogen and carbon can be effective transports of the chemical potential energy of hydrogen. The liquid forms of such fuels can be readily contained in tanks at standard temperatures and modest pressures. These liquid fuel energy densities are superior to those of hydrogen, requiring smaller tanks. Methanol is a reasonable substitute for gasoline, favored by Nobel laureate George Olah; dimethyl ether can substitute for diesel fuel. Both require carbon sources, perhaps from new carbon-capture facilities at new coal plants. That carbon will be eventually released into the atmosphere when the fuel is burned; we borrowed it on the way out of the coal plant.

But what happens if we stop burning coal? Project Green Freedom proposes capturing CO2 from air, but its density is only 0.035% of air. Nitrogen is plentiful in the atmosphere (78%) and returning it to the air is nonpolluting. Consider ammonia for fuel. Ammonia is the second most common industrial chemical.


Ammonia is used to make fertilizers and even directly in farming, injecting liquid ammonia directly under the soil. Fertilizers from ammonia are responsible for enhancing agricultural production that feeds two-thirds of the global population. More than 1% of all primary energy is used to produce ammonia.

Ammonia Pipelines

Ammonia is such a common industrial chemical that pipelines distribute it in the farm states. It is transported and contained in tanks under modest pressure, similar to propane. It is potentially hazardous to inhale; a 1% concentration inhaled for 1 hour has a 1% fatality risk. However ammonia is readily detected by its odor, and being lighter than air it rapidly dilutes in a spill. Unlike gasoline or diesel fuel, it does not catch fire in an accident; the ignition temperature is 650 C. Considering all such risks, the health hazard of ammonia is about the same as gasoline.

Ammonia fuel



Ammonia has been the fuel for the record setting X-15 airplane. The University of Michigan has an ammonia-fueled truck. In Belgium in World War II ammonia fuel powered buses. Today’s flex-fuel internal combustion engines are able to run on a variety of fuels ranging from gasoline to E85 (85% ethanol, 15% gasoline). Reportedly flex-fuel engines can be adapted to run on a miscible mixture of ammonia and a small amount of dimethyl ether or ammonia mixed with reformed ammonia (NH3 -> 3/2 H2 + N2) on the way to the engine.

Fuel cells are an alternative to internal combustion engines. Hydrogen fuel cells combine with oxygen in air to generate electricity for vehicle batteries and motors. The direct-ammonia fuel cell uses ammonia directly, stripping the hydrogen from the ammonia on the hot surface of a ceramic electrolyte.

Ammonia production

The reverse process can manufacture ammonia from streams of nitrogen separated from air and hydrogen created by dissociation powered by high-temperature process heat and electric power from LFTR electric power generators.

Solid State Ammonia Synthesis

The hydrogen electrolysis or thermal dissociation step can be eliminated via solid-state ammonia synthesis, operating like a solid-oxide fuel cell, but in reverse. It similarly has a ceramic proton conducting membrane. It has the advantage that there is never any separated explosive hydrogen gas and it operates at low pressure. Nitrogen is obtained from the ASU (air separation unit).  Water supplies the hydrogen. The ceramic membranes are tubes and the SSAS can be scaled up by using more tubes. The SSAS process is safer and cheaper than the standard Haber-Bosch process. The key cost advantage is that SSAS is projected to make ammonia at 6800 kWh per ton. With factory reactor production, LFTR electric power is projected to cost $0.03/kWh, leading to ammonia costs of about $200 per ton. This is half the cost of ammonia produced today from natural gas, and it avoids the release of carbon dioxide in that widespread manufacturing process.

The heat of combustion is the thermal energy that would be released in an internal combustion engine. Taking account of the different prices and heats of combustion of ammonia and gasoline illustrates that energy from ammonia is one-third the cost of energy from gasoline.

Ammonia fuel cost

Relative costs

How might this lower energy cost translate into vehicle fuel costs? The left bar chart illustrates the typical cost components of gasoline in California. Most of the cost is for the crude petroleum that provides the energy content of the gasoline. The refining costs are only about 10%, even though refineries are complex, expensive investments. We don’t really know the cost of SSAS chemical plants, but simply assume that the talented chemical engineers who built petroleum refineries can build similarly large ammonia production plants at about the same cost.

In summary, ammonia liquid fuel can replace petroleum liquid fuels for surface transport vehicles, at less cost, eliminating CO2 emissions.

This article is derived from a presentation by Robert Hargraves, Darryl Siemer, and Kirk Sorensen, entitled Nuclear Ammonia: Thorium’s Killer App, presented October 11, 2011, at the iTheo annual meeting at City College of New York.

14 Responses to “Nuclear Ammonia”

  1. TerjeP says:

    If you did this using conventional electricity (ie not LFTR) then presumably you double the cost of the ammonia. However the price chart above suggests this would still be cheaper than petrol (gasoline). That been the case this approach is not commercially dependent on LFTR. So why isn’t it happening regardless?

  2. TerjeP says:

    p.s. In terms of energy density on a volumetric basis how does ammonia compare to petrol (gasoline). Will my car need a bigger tank?

  3. James Rowland says:

    It seems the simple answer is yes, you will need a bigger tank. I’m not quite sure how much bigger though, having found several different figures:

    According to the Wikipedia page on energy density, petrol and diesel have energy densities of around 35MJ/L, whereas ammonia is 11.5MJ/L, significantly lower than the 17MJ/L quoted above. I found another source that states it is 15.6MJ/L.

    They all allegedly refer to combustion to nitrogen and water and don’t include oxidant mass. I can’t figure out the discrepancy – unless some of them are just wrong. Does anyone here have an authoritative figure or an explanation of the different numbers?

    Anyway, I guess you would need pressurized tanks similar to existing automotive liquid propane tanks but larger (since propane has an energy density of 25.3MJ/L.) How much larger would depend on which of the above is the right number. :)

  4. James Rowland says:

    I found some data for automotive LPG tanks. Typical empty mass seems to be in the 20-45kg range depending on capacity. That’s a LOT heavier than non-pressurized tanks, and a significant fraction of vehicle mass.

  5. TerjeP says:

    Brent – thanks for the video.

    At a guess I would say there is a form of Nash equilibrium at play. Car makers make cars that run on the fuel that fuel retailers sell. And fuel retailers sell the fuel that cars run on. Trying to shift to something different entails substantial risk on the part of one or both of those parties and inconvenience for any consumer that decides to come to the party. At a guess LPG is probably a cheaper and more established alternative to petrol so there isn’t much niche left for ammonia. Still if there was a very big cost advantage the inconvienience is something people would wear and the inconvenience would decline as the offering scaled up.

    James – thanks for the numbers.

  6. Maslo says:

    How this ammonia fuel compares to dimethylether (DME) fuel?

  7. Jim Baerg says:

    TerjeP: IIUC those low costs for ammonia production are based on using Solid State Ammonia Synthesis, which is a recent development & still somewhat experimental. If the low cost non-fossil ammonia production works, it would first displace the current fossil fuel based ammonia production for fertilizer & any fuel use of ammonia would start with farm machinery where there is an existing distribution network.

    Rowland Re: LPG fuel tanks. Are those weight figures for the all metal tanks which have been standard for decades or the more recent designs which use high strength carbon fibre reinforcement to allow the tanks to be lighter?

    Would ammonia fuel be all that environmentally benign?

    My understanding is that current nitrogen fertilizer use creates problems with A) eutrophication of water bodies & B) more N2O getting into the atmosphere where it acts as both a greenhouse gas & an ozone destroyer. I would expect spills from ammonia fuel systems to add to this issue. Does anyone know of an analysis comparing these issues to problems with other fuel options?

  8. Jeff S says:

    Has anyone ever done any research on using biomass as a source of carbon (and hydrogen), but not directly converting it to something like Ethanol, but instead, denaturing cellulose, and combining it with hydrogen from a source like the LFTR-powered hydrogen “refinery” in this article?

    I don’t know enough chemistry to be able to tell if this would be worthwhile, but it seems to me like by combining biomass and hydrogen to form something like methanol or dimethyl ether, you might be able to “multiply” the biomass energy by the addition of the hydrogen?

    Again, I don’t know that much about chemistry, just the basics. I observe this: Cellulose is C6H105. Methanol, according to the diagram above, is CH3OH. So, Cellulose provides us with *six* carbon atoms, per molecule. Each molecule of Methanol needs only 1 carbon atom. Cellulose provides us with 4 Hydrogens, but for 6 molecules of Methanol, you’d need 24 atoms of hydrogen. The cellulose provides us 5 atoms of Oxygen, but for 6 molecules, we’d need 6 – however, the hydrogen “refinery” would be producing “waste oxygen” which could be captured to make up the deficit.

    So, am I correct in thinking that by taking cellulose from plants (hemp, switchgrass, etc), and adding in the missing hydrogen from a LFTR, we could produce 6 molecules of methanol for each molecule of cellulose? Per kilogram of input cellulose, how many kilograms of methanol would you get as output (the addition of the “missing” hydrogen and oxygen would increase the mass slightly – maybe from like 1kg to 1.1kg or something?), and how much potential energy would that mass of methanol have compared to the original kilogram of cellulose?

  9. Steve Burrows says:

    The safety and liability issues involved with using ammonia as a fuel would be almost as staggering as nuclear! Release of ammonia kills in the most horrible way imaginable, just a small whiff will send you head over heals in pain, this isn’t the diluted stuff under your kitchen sink, pure ammonia is just too difficult to handle as a transportation fuel.

    Keep the uses of ammonia to carefully controlled industrial uses, use by the public is asking for too much trouble. When released ammonia starts killing people in traffic accidents that they should have easily survived, the way it was made will take the blame.

  10. KAP says:

    I totally agree with both the comments about safety of ammonia (it’s very, VERY dangerous stuff), and the large greenhouse gas potential when inevitable incomplete burning produces N2O. Not a good idea.

    I’ll stick with H2 and fuel cells. And BTW, a major breakthrough on the oxygen-side catalyst for both electrolysis and fuel cells was made just this week. The new catalyst is 10 times (!!) more efficient than anything previously known. See

  11. Ammonia is not a heat trapping greenhouse gas. NOx emissions are a concern in any high temperature combustion process. Ammonia is added to the combustion process for coal burning and wood burning power plants, to reduce NOx emissions.

  12. The hazards of ammonia are different but equivalent to those of gasoline. A 2009 Iowa State University analysis concludes “In summary, the hazards and risks associated with the truck transport, storage, and dispensing of refrigerated anhydrous ammonia are similar to those of gasoline and LPG. The design and siting of the automotive fueling stations should result in public risk levels that are acceptable by international risk standards. Previous experience with hazardous material transportation systems of this nature and projects of this scale would indicate that the public risk levels associated with the use of gasoline, anhydrous ammonia, and LPG as an automotive fuel will be acceptable.”

  13. G.R.L. Cowan says:

    Gasoline-ammonia energy density ratio, 2.861 (Raso Enterprises), 2.839 (me) (but my comparison was of deltas ‘G’, with 3E3MP representing gasoline).

    My position, of course, is that we don’t have to settle for “hazards … equivalent to those of gasoline”. We can have personal vehicle propulsion with nuclear-style safety.

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