Nuclear Ammonia

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

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.

Comments

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30 Replies to "Nuclear Ammonia"

  • Fred
    November 7, 2011 (9:41 pm)
    Reply

    Ammonia, No. Methanol, far superior to Ammonia, cheaper to make, and simple & easy to handle, and a liquid at STP. Easily stored in flimsy plastic containers, as they sell it in grocery stores. They are widely using it in China for vehicles, producing Methanol from Coal. The DOE built an IGCC Coal Power plant that could co-produce Methanol for $.50 per gallon. Methanol spills are trivial, and quickly dissipate into the atmosphere or are metabolized by bacteria. A dilute methanol spray actually improves plant growth. And though it has an energy density half of gasoline it will burn at almost double the efficiency of gasoline in a converted engine. Optimized Methanol Engines are actually more efficient than diesels, and much cleaner, with a much wider island of high efficiency than the diesel, as well as cheaper using port fuel injection rather than direct fuel injection.

    And the EPA estimates there would be a 95% reduction in fire deaths & injuries if gasoline was replaced with Methanol. And you can ship Methanol easily in pipelines and in tankers, as Methanol actually cleans the pipelines.

    And the toxicity of Methanol is greatly exaggerated. It is actually a poison to humans and other primates, because the enzyme we have evolved to metabolize the ethyl alcohol in fruit, converts methanol to Formic Acid in the blood which gradually over a period of 8-48hrs builds up to the point that it can destroy nerve tissue, possibly causing blindness. Treatment is simple,by taking 4 standard drinks of alcoholic beverage and one drink per hr, by a fomepizole tablet, or by taking folate.

    The obvious thing is to make Methanol Carbon Neutral by converting waste Biomass to Methanol, with Nuclear Hydrogen and Nuclear Electricity. And transfer 100% of the Biomass carbon to liquid fuel carbon rather than stupidly waste 80% of the Biomass carbon, as in Ethanol fermentation, or even more stupid burning the Biomass for Electricity, as they like to do in Greenie Germany & Denmark, while destroying food crop land producing biodiesel and agro-ethanol.

  • P.M.Lawrence
    November 8, 2011 (6:23 am)
    Reply

    Fred, some of your comments about methanol, although accurate, are not to the point: the suggestion here was that ammonia would be a convenient way to "package" nuclear energy for free standing uses like vehicles, convenient because its raw materials were readily obtainable and convertible and its combustion products were non-polluting. Methanol is all the things you say, but it falls short by the specification used here. Its feedstock needs a carbon source, which is awkward if it is obtained from the atmosphere directly or via plant matter (which must be gathered), and if not it still involves fossil carbon (which counts as polluting by some standards). Certainly, methanol is better by all the other criteria you outlined – but it's still up to the author to choose the criteria, to ask the question he has in mind. So I think the way to go is to run with these criteria, and maybe use a reductio ad absurdum to show that there is more to all this. After all, isn't hydrazine better than ammonia, because it uses the same raw materials, has a higher energy density, and is easier to keep liquid? Isn't hydrogen peroxide also better than ammonia because it is even easier to make and is also a liquid? And aren't the two of them together even better because you get even more of their energy back?

  • Robert Hargraves
    November 8, 2011 (6:39 am)
    Reply

    Fred and P.M.Lawrence, Yes, methanol would be a great fuel. It was used in the Indianapolis 500 motor races for decades because it was safer than gasoline in a crash. It is certainly easier than ammonia to use with the existing infrastructure of pipelines, filling stations, automobiles, and trucks. I'm not so much advocating ammonia as laying out some options. The interesting issue with methanol is getting the carbon in a carbon-neutral way.

  • Russ P.
    November 14, 2011 (10:45 pm)
    Reply

    Robert: I recall reading in one of your recent presentations that methanol (even produced with LFTR) can't put a serious dent in our dependence on foreign oil. I was a bit disappointed by that. Do you still stand by that? Would you elaborite? Thanks.

  • Anonymous
    November 17, 2011 (6:31 pm)
    Reply

    Maybe this technology could be interesting for you:
    http://de.wikipedia.org/wiki/N-Ethylcarbazol

    Unfortunately, the article is in German. But check out the references, some article are in English.

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