Ammonia: a New Year’s paean

Synthetic ammonia from catalysed hydrogen: yes ,iy’s important

WTF? Has Wimberley finally taken leave of his diminishing senses? Why laud a commonplace and unpleasantly acrid standard chemical, used to make fertilizer and explosives, and still popular as a cleaning agent with traditionalist housewives in Spain and Brazil? (The nasty smell tells germs you mean business.)

Hear me out, kind readers. Ammonia is about to take its place as a worthy piece of the complex jigsaw puzzle of the energy transition.

This will be down to its additional potential use as a carbon-free fuel. Burn ammonia, in an engine or fuel cell, and you ideally get:

4.NH3 (ammonia) + 3.O2 (oxygen) → 2.N2 (nitrogen) + 6.H2O (water)

In an engine, in practice you also get some nasty nitrous oxides, NOX: controllable by clever engine management, scrubbing the exhaust with more ammonia, or reforming to hydrogen just before burning.

Ammonia is not a greenhouse gas, and nor are its main combustion products. So it’s a candidate for a storable renewable fuel to replace oil-based liquid fuels and natural gas. The rivals are plant-based liquid biofuels (diesel, ethanol, kerosene), biogas from digesters fed with biomass, and catalytic hydrogen.

In this competition it has some attractive technical characteristics. Ammonia’s energy density is half that of the hydrocarbons, but twice that of hydrogen. This is a major issue for aircraft, but not really for the other major potential uses: heavy trucks, ships, and power stations.

Its boiling point is -33° C. Compare butane: – 12° C; propane: – 42° C; methane/natural gas: – 164° C; hydrogen: – 253° C. The last two require very expensive refrigeration plants to reach the liquid state, and expensive refrigerated transport to stay in it. Ammonia, like butane and propane, can be pumped around as a gas at ambient temperature, or liquefied by standard compressors and transported in simple pressurised containers, again at ambient temperatures. It’s clearly a better bet all round than hydrogen. Methane has the benefit of incumbency: a massive legacy piped distribution system, even to many houses. But methane is a greenhouse gas, in the short run twenty times as powerful as CO2, and leaks can’t be avoided.

[Update 2/1/2019]Ammonia does not emit greenhouse gases at all. The others  burn sustainably sourced hydrocarbons; the CO2 is recycled back into plants. These are not morally identical. Partly it’s the time lag. Partly it’s because net zero won’t be enough, and we need to enlist the biosphere as a net carbon sink, through reafforestation and burial. [/update]

The existing ammonia industry of about 150 MT a year may be small by oil standards, but it is quite big enough for the handling and distribution technology to be reliable and mature. It doesn’t need anything new to become a fuel.

The main lack is engines and fuel cells to burn it. You can’t go out and buy a marine diesel designed to burn ammonia either by itself or in a dual-fuel configuration. This is not SFIK a major engineering challenge – create a demand, and the engines will come quickly.

The main factor militating against ammonia is cost. Ships in particular burn a vile sludge called heavy bunker fuel, the residue left after all the good fuels have been refined away. It’s cheap, and likely to stay that way. Besides, there is just now no climate reason to go for ammonia. It’s produced from oil and gas by the Haber-Bosch process, which vents the carbon as CO2 anyway.

Ammonia synthesis demonstration plant source JGC

Things are changing here. A team in Japan have built a working pilot plant using catalysed hydrogen as the feedstock. So a renewable production chain for ammonia now looks feasible: and hence a pathway to sustainable decarbonised shipping.

Cost? I’ve no idea, and ruthenium catalysts are presumably expensive. But cheapness is not a reasonable demand to make of a process at this exploratory stage. The normal pattern is that once a technology works, it can be made cheaper with experience and scale.

How does this fit into the wider energy transition? Very nicely, but it needs some background.

Let’s do a crude thought experiment for the UK electricity supply. Recall that the baseline 100%-renewable electricity scenario is now wind, solar, transmission, and pumped hydro storage (see Blakers for Australia). Simplify this even more, and take an initial solution for the UK without solar, which we will add back if it’s cheaper. UK peak electricity demand is 48 GW in winter. Allowing a 50% capacity factor, we need 96 GW of turbines, a doable increase from the 20.5 GW today. But there are lulls even in winter. The late David Mackay did some back-of-the-envelope math in 2008 for a 5-day maximum lull and 33 GW of wind at 33% CF, and the pumped storage needed was 1,200 Gwh. Scaling up we need 5,760 Gwh. It’s a mere 30 Gwh today, so it’s a truly massive expansion, so large as to look impossible.

Battery to let

There are plenty of ways to cut this. The storage can be in Norway, which has a very large supply of steep, wet and unpopulated mountains. The price is adding undersea cables at £1.4 bn per GW capacity, on top of what you pay the Norwegians for the electricity.  You can add solar, whose variation is mainly diurnal and on longer timescales is uncorrelated or inversely correlated to wind. (BTW, if you can handle the variation in a large wind park, adding a more consistent solar one logically poses few problems. The “solar needs storage” meme is largely bunk.) You can hook up underused car batteries, V2G in the trade: range anxiety by purchasers will ensure massive excess capacity. There’s demand response (contracts to cut usage on request), and intelligent management of water heaters, a/c, and freezers. Finally, there is conversion to storable fuel, which is where we came in.

You can also tackle the issue by just building more wind turbines at a modest £1.5 bn per GW onshore (IRENA, pdf page 94). This will lower capacity factors. But so what? On the LCOE cost metric, which assumes full takeoff, wind is already competitive with fossil generation in most countries and much cheaper in some, including the USA. There is a steadily growing cost gap that allows ever higher curtailment. 2.5c/kwh LCOE with a drastic 50% curtailment is still only an acceptable 5c/kwh net.

Whatever mix is settled on for firming a wind-and-solar dominated electricity supply, it will very probably include significant overbuild of nominal capacity against peak demand, and massive overbuild against trough demand. I don’t think 2 x is unrealistic economically.

This means that in any such world, there is certain to be large oversupply for significant periods when the wind is blowing hard, or the sun shining from a clear summer sky. This electricity will be practically free at the point of production, and available for the low cost of transmission.

Similar but more professional thought experiments have been carried out elsewhere. These use hour-by-hour simulations of grid demand, and recently they have been coming up much more cheerful than Mackay. A lot of money and effort has been going into P2X projects, especially in Germany (pdf). The acronym stands for “power to (some) synthetic fuel.” The working assumption is that there will in due course be a lot of very cheap surplus wind and solar power to use.

The cost-benefit calculations will get complicated. My guess is that it’s a race between green ammonia and green methane, with pure hydrogen a distant third because of the transport problem. The crucial variables are whether methane is taxed to pay a proper carbon price for its leaks, and the comparative efficiency of the upgrade reformers. On a level playing field, ammonia looks pretty good.


Wonkish note on methodology

My thought experiment is crude and many of the numbers are guesses, so don’t take the results too seriously. However, I defend the method. What I remember from a brush with linear programming years ago is that you start an optimisation with a simple non-optimal solution, and tweak the variables from there until it looks good. This is not guaranteed to work but it normally does. Under uncertainty, it is sensible to start with a solution of known feasibility, say technologies x and y. This allows you to tweak with hypotheticals: what if technology z also works? In my example x is wind, y is solar, and z is synthetic green ammonia.

Nuclear power offers a case where the technologies are not well-behaved and there may be several local optima. If you start with wind and solar, adding nuclear doesn’t help, as you want despatchable firming not baseload. Start with all nuclear, and adding wind and solar doesn’t help, as they aren’t despatchable backup. They aren’t complements at all, which helps explain the bitterness of the disputes around nuclear (see Jacobson v. Clack). It’s nuclear or renewables, not both. These disputes are now academic in the pejorative sense, as nuclear power is hopelessly expensive and slow to build.

Author: James Wimberley

James Wimberley (b. 1946, an Englishman raised in the Channel Islands. three adult children) is a former career international bureaucrat with the Council of Europe in Strasbourg. His main achievements there were the Lisbon Convention on recognition of qualifications and the Kosovo law on school education. He retired in 2006 to a little white house in Andalucia, His first wife Patricia Morris died in 2009 after a long illness. He remarried in 2011. to the former Brazilian TV actress Lu Mendonça. The cat overlords are now three. I suppose I've been invited to join real scholars on the list because my skills, acquired in a decade of technical assistance work in eastern Europe, include being able to ask faux-naïf questions like the exotic Persians and Chinese of eighteenth-century philosophical fiction. So I'm quite comfortable in the role of country-cousin blogger with a European perspective. The other specialised skill I learnt was making toasts with a moral in the course of drunken Caucasian banquets. I'm open to expenses-paid offers to retell Noah the great Armenian and Columbus, the orange, and university reform in Georgia. James Wimberley's occasional publications on the web

8 thoughts on “Ammonia: a New Year’s paean”

  1. Hurrah, hurrah!!!

    I think I even understood some of it. You’re basically saying, renewables are busting out all over, and that ammonia is a way to store some/more of that energy? It really *does* sound exciting.

    Just looking at the long term – I know there are people who want to explore space. (I am cool with the research aspect, but have no interest in ever actually leaving. Until, well, you know…) Will they need nuclear for that or could you do that with renewables too? I guess you could make solar out of any star? Or is there really wind, and you could sail? (Like I said, space isn’t my thing. I just like to gaze at it. This is probably a really dumb question. I should be embarrassed and I’m just not.)

    And Happy New Year!!!

    1. And Happy New Year to you too.

      Rockets aren’t too picky. Wikipedia says that ammonia has been used as rocket fuel, along with hydrogen, hydrazine and other stuff you don’t want to let into your home (see Charles Stross’ great yarn A Tall Tail. Since you can get renewable hydrogen and ammonia, I daresay other renewable fuels could be synthesized too. But the total demand is so small it scarcely seems worth it.

      Solar sails? Fine, but how do you get back? It’s not like sailing into the wind, where the water resistance blocks sideways motion in the direction of the wind.

      The only (very) remotely feasible interstellar propulsion I have heard of is the Bussard ramjet, which needs a fusion reactor as its power source. I suppose that counts as renewable, on the same basis as magic warp drives.

      I suggested here that interstellar manned flight is too dangerous anyway because of all the space junk in the way. None of the commenters gave me a good reason to think I was wrong, though I had to rewrite the post in the light of other points.

      1. As per usual, my mind is blown by all these concepts. I won’t have a response for several weeks by which time we will all have moved on.

        “Ergo, any alien civilization surviving long enough to launch interstellar ships would refrain from doing so on ethical grounds. QED.” See now I have to think about that too. Whoa Nelly.

        Meanwhile, I will say, although I lack interest in visiting space personally, I am already upset that we are *littering all over it.* And we aren’t even in it yet!!!????? *What* is going on and *who* is in charge around here? Seriously.

        I have a very half-baked proposed international law that says, whoever wins a war has to pay for all the cleanup. (There are some practical problems. Like, whose fault it was that it started, for one. Got to count that.) Another could be, no space travel for humans until we clean up our act here.

        Still, again, thank you for bringing some hope to the hope-hungry!!! I need to subscribe to some kind of science magazine so I can be less ignorant. I wonder which one.

  2. My impression is that although ammonia might be nice from an energy-storage point of view, some of its other characteristics might make it less than ideal in widespread use. Seriously corrosive, toxic (hence the use as cleaner) and combustible/explosive (including situations where ammonia eating something else generates enough heat to cause a chain reaction). A fair amount of ammonia is used in industrial refrigeration, and such not uncommonly make news by blowing up. (Indeed, our entire CFC problem originated in the search for refrigerants that weren’t so resolutely toxic and explosive.)

    I’m sure that with work these issues could be addressed satisfactorily, but I do wonder if that would be the best use of resources.

    1. A very common accident in early industrial cities was steam boilers blasting through the walls of the factories they were housed in when they sprang a leak. Gasoline is horribly flammable. Flour is an an explosive as a suspension in air. We live with these risks. The large existing ammonia industry seems to operate with acceptable safety – it’s not its fault if fertiliser is turned into DIY explosive by terrorists.

      [Update] Methane regularly causes serious explosions too – see Ronan Point. Is ammonia really more dangerous? And hydrogen is surely worse (Hindenburg airship).

      Industrial refrigeration facilities are numerous and dispersed. They will be supervised by technically qualified workers, but not ammonia experts. The uses my scenario envisages are concentrated in larger facilities where you can reasonably demand a higher level of expertise: the boiler-rooms of ocean-going ships, power stations, storage tank farms, and of course the synthesizer plants. [/Update]

      1. On the other hand, public policy has very deliberately limited the large-scale transport of LPG and LNG because of such concerns, and the siting of terminals and storage facilities. I’m not saying you couldn’t do it, just that with many portable energy storage mechanisms available, getting this one right may not be particularly cost-effective.

        On the other hand, if we’re thinking more along the lines of a war footing where you throw everything at the wall to see what works, then sure.

  3. LPG, in the form of bottled butane, is a standard consumer good round here in Spain – that’s how I and my neighbours run our kitchen hobs and in many cases water heaters. It’s obviously a regulated business, and you get the bottles from oil companies and their petrol stations, not supermarkets or corner stores. Domestic gas installations are supposed to be inspected regularly, creating fertile ground for cowboy operators.

    I do remember looking at a British DIY site with detailed instructions for building projects of many types, including plumbing, drains and electricity. The page on gas just said: don’t. DIY gas work is illegal and dangerous.

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