Fueling With Ammonia

There’s a major push now to find energy sources with smaller carbon footprints. The maritime shipping industry, according to IEEE Spectrum, is going towards ammonia. Burning ammonia produces no CO2 and it isn’t hard to make. It doesn’t require special storage techniques as hydrogen does and it has ten times the energy density of a modern lithium-ion battery.

You can burn ammonia for internal combustion or use it in a fuel cell. However, there are two problems. First, no ships are currently using the fuel and second most ammonia today is made using a very carbon-intensive process. However it is possible to create “green” ammonia, and projects in Finland, Germany, and Norway are on schedule to start using ammonia-powered ships over the next couple of years.

Switching over, though, will be an infrastructure challenge. Ships consume about 300 million tons of fuel each year, and most of that is diesel which has twice the energy density of ammonia. Ports will need storage and filling equipment to make the switch practical.

To make ammonia takes hydrogen and nitrogen. Most commercial hydrogen is made by reacting methane which releases carbon as a byproduct. However, hydrogen can be split from water using green energy, too, and that will be another key factor in making ammonia fuel work for companies trying to reduce carbon emissions.

You might think this is a new idea, but Germany used ammonia in 1942 to fuel public buses in occupied Belgium. The buses used an internal combustion engine that ran on a combination of ammonia and coal gas. The X-15 aircraft also used ammonia as one component in the fuel that powered its rocket engines.

Storing ammonia is easy, but there are some easy ways to store hydrogen, too. We’ve seen some fuel cell drones, but nothing running on ammonia. At least, not yet.

68 thoughts on “Fueling With Ammonia

      1. Ammonia is nothing compared to the use of sulfur dioxide as a refrigerant.
        I tried to mangle an old fridge to become a keg beer dispenser. In doing so I cracked the refrigerant pipes. We had to evacuate the apartment until it all leaked out. My housemates were not pleased.

      2. Dormitory refrigerators still use ammonis. I had one dump all its gas in a minute or so. It stunk, we carried it outside, no harm. Ammonia floats like helium. In most circumstances it is safer than gasoline.

    1. Used a mix of hydrogen peroxide and ammonia to clean gunk out of an old camera lens. More windows shall be opened next time!

      When these ships get old, presumably they will be stinky also.

    2. Ammonia is extremely toxic to aquatic life, even in dilute amounts, so using it to power ships is the dumbest idea imaginable.

      Searching around, it seems you only need about 2 ppm levels to start poisoning fish.

      1. Its not like leaking oil, diesel etc is good for the fish either…
        But with the vast volume of the ocean even a few bad leaks of anything won’t cause harm unless its never fixed and stays in the same spot so the local concentration can really pick up…

        Not that any leaking is good, but lets be sensible here and realise we dump toxins in the oceans from soo many sources, including lots of ammonia based fertilisers… Which we should be working to reduce as much as possible, but because the ocean is so vast it can take it rather well as a distributed load. So if you get ammonia cycle being done in a cleaner way than diesel its a good net gain for the planet, and probably the ocean directly too.

        1. Well, diesel oil isn’t particularly harmful, and it tends to float to the surface.

          Ammonia and water mix together, so an ammonia spill – especially in an accident – poisons the local environment much more effectively. The waters around harbors and fueling depots will have constantly elevated concentrations from regular leaks and spills, and elsewhere you’ll have the occasional ship sinking which releases a whole bunch of ammonia at once.

          1. The waters around most harbours are already loaded up with ammonia, because many of them are on river delta and all the fertiliser runoff makes the rivers rather full of it..

            The fact diesel floats doesn’t make any safer for the critters, just changes which critters it harms/kills easily – the air breathers and sea birds come off terribly after being coated in oil based spills, while the deep ocean fish won’t give a crap (at least if its tidied up – leave it long enough and it will kill many of them too as the blocking of sunlight, gas exchanges between the water and air, etc, end up changing the ecology, killing off their food sources)..

            In no way am I saying Ammonia is without risks, safe as can be. But equally its got potential to be used safely, and if we wrote off anything that polluted the environment when things go wrong we would have to be back in caves using stone tools… Heck even when everything works perfectly ICE engines are hideously polluting, and marine diesel tend to be the worst of any ICE on many counts, because the regulations to make them clean up after themselves would add too much financial burden, so they can’t possibly be held to the same standards as road vehicles…

            I’m yet to be convinced Ammonia really is the future, but it has potential enough to be worth looking at – Personally I think for those energy dense needs hydrocarbon fuels are likely to remain nearly forever, just sourced in a different way that makes the whole cycle less harmful (maybe even a net gain – if you are making artificial fuels out of the atmosphere (directly or via those lovely green leafy things) you can also make plastics, and lubricants which means potentially and end to fracking and the like, and the large carbon footprint and environmental cost of such activities…

            Also worth pointing out that Nuclear cargo ships would actually make a great deal of sense, done right its safer than any other fuelling method, and the ships are big enough to easily use such a power source. Not like its worth worrying about it from the dirty bomb point of view either, lots of easier and less obvious methods to get radioactive crap to spread around explosively, and should one of them sink its going to make no real difference to the ocean it sinks in, a tiny warmer spot for some decades no different to the many other warm spots on the ocean floor (probably much colder than them actually)..

        2. https://en.wikipedia.org/wiki/Oil_pollution_toxicity_to_marine_fish
          >Fish are able to readily metabolize 99% of PAHs to a more hydrophilic metabolite through their hepato-biliary system. This allows for the excretion of PAHs.

          In contrast:

          >Ammonia is converted to carbamoyl phosphate by the enzyme carbamoyl phosphate synthetase, and then enters the urea cycle to be either incorporated into amino acids or excreted in the urine.[103] Fish and amphibians lack this mechanism

          Fish rely on directly excreting ammonia into the surrounding water, so they have no mechanism to eliminate it. If the surrounding water does contain ammonia, they absorb it and die from it.

          1. You can’t clean it up. An oil spill can be scooped off the surface. Ammonia dilutes into water, so you’d have to somehow treat cubic kilometers of sea water to do anything about it.

          2. Ammonia is alkaline in water. CO2 is acidic in water. With our modern 400+ ppm atmospheric CO2 the ocean has been getting more acidic. Seems like a certain amount of NH3 spillage might actually counteract the acidification problem somewhat.

      2. Ammonia is very quickly broken down in to nitrite (toxic to marine life), then nitrate (a little toxic but not bad), then further from there.
        It doesn’t stick around long in a marine environment because the bacteria present there break it down into less toxic chemicals very quickly.
        At least that’s what happens in my aquarium.

        1. That’s true when there’s tiny amounts of ammonia in the water. When there’s a big spill, the bacteria die and it takes a while for them to recover.

          Kinda like how a bottle of wine can turn into vinegar, but a bottle of vodka won’t, because the bacteria that can eat ethanol can only stand so much of it.

    3. And meth labs will spring up around port facilities instead of agricultural facilities… On a side note when I was a kid a tanker truck of anhydrous ammonia (bound for a nearby farm I imagine) crashed and spilled its cargo like a mile away and the air was basically unbreathable outdoors for hours.

    1. Not so when the fossil fuels we’re currently using have to go through engines that turn 50~66% of the fuel’s energy into waste heat. There’s plenty of room for using less-dense energy sources that can be converted to kinetic energy more efficiently there. Obviously this is unlikely to be an improvement if ammonia is powering an ICE, but the fuel cell idea could yield an improvement.

      1. Marine diesel engines are already the most efficient combustion engines around, because they’re so big that it starts to resemble an ideal heat engine cycle. All the friction and heat losses are proportionally smaller in a big engine, to the point that a fuel cell isn’t actually any better.

  1. It doesn’t produce CO2 but doesn’t it produce NO2, N2O etc? Aren’t these bad?. If you have a process where it produces N2 instead, this would be harmless but this will reduce it’s energy density.

      1. I thought the nitrogen oxides from hydrocarbon combustion weren’t formed as part of the main combustion reaction, but as byproducts of N2 oxidation? I don’t know how much N2 gets oxidised but I don’t think N2 is very reactive compared to hydrocarbons. As the main combustion reaction with ammonia involves oxidation of NH3, I would have thought that more nitrogen oxides will be formed with ammonia than with hydrocarbons (unless the oxidation process somehow produces N2 rather than nitrogen oxides).

        1. To my understanding, nitrogen oxides are formed in particularly high temperature environments (don’t know off the top of my head what temperature that is). It doesn’t help that in the quest for high efficiency or performance generally requires high peak temps. If ammonia is cooler burning (I don’t know if that’s the case) than typically used hydrocarbons, the production of nitrogen oxides could be reduced.

          1. yep huge capacity low compression engines produce less nitrogen oxides, these have only became a bigger issue in recent years especially with innovations like direct injection letting manufacturers push compression ratios and lean burn strategies (thus heat n pressure) higher than ever before.

            obviously huge capacity low compression engines have their downsides.

          2. @denis: NOx production with HC fuels is always dependent on high temperature. N2 does not really like to burn. Unfortunately thermodynamics require high temperatures for efficiency. But low compression is a way to lower the efficiency (and NOx production).
            Unfortunately ammonia brings reactive N with itself, in short nitric acid is produced by burning ammonia what delivers NO2 which is dissolved in water to form HNO3.

          3. High temperature AND high pressure AND an excess of oxygen. If there’s enough fuel to burn, the HC burns first and consumes the available oxygen, so NOx cannot be made.

            A diesel engine is bad with NOx because it’s lean running. When you add enough fuel to consume the available oxygen, it leaves little soot kernels by incomplete combustion and you’re rolling coal.

        2. Bit tired right now so correct me if I’m wrong but….
          I haven’t read this article but for it’s conclusion: https://www.sciencedirect.com/science/article/pii/S1540748918306345
          In the abstract they say that “Ammonia can be used as a fuel but there are several challenges in ammonia combustion, such as low flammability, high NOx emission, and low radiation intensity”.
          But there is mention that “Challenges such as low flammable characteristics and fuel NOx emissions can be overcome by the knowledge of the dynamics and chemistry of combustion”.

          If we think it through: Let’s assume that we use Harber-Bosch synthesis to acquire ammonia out of thin air:
          N2 + 3H2 2NH3

          Now we combust the NH3 into N2:
          4 NH3 + 3 O2 → 2 N2 + 6 H2O (g)
          According to “credible” source (wikipedia):
          4 NH3 + 5 O2 → 4 NO + 6 H2O but this only happens in the presence of a catalyst. However if the combustion of ammonia is incomplete, it will surely release some NO and NOx:
          2 NO +O2 → 2 NO2

          Now if we release NO2 into the atmosphere, there will be moisture with which it could react in the following manner:
          2 NO2 + H2O → HNO2 + HNO3

          Since achieving complete combustion to N2 in reality, they are researching so called deNOx technologies like the one behind this paywall: https://www.nature.com/articles/s41557-019-0356-0

          If we take the N2 from the atmosphere such as the Harber-Bosch process does, releasing it back into the atmosphere would not change it’s composition in any noticeable manner I’d assume, unlike releasing fossil-fuel CO2.

          In conclusion, it may cause the formation of NOx and acid in the atmosphere, but if the deNOx technology gets developed far enough, you’ll have a cheap source of HNO3.

          1. Since the energy density of ammonia from what I have read so far is about half as much as diesel fuel, and according to yahoo finance:
            “One of the largest container ships to call on the U.S., the CMA CGM Benjamin Franklin, carries approximately 4.5 million gallons of fuel oil. Ship fuel capacity is generally converted to volumetric measurement. The equivalent on the Ben Franklin would be close to 16,000 cubic meters.” [1]

            This would mean the Ben Franklin, with ammonia, would use roughly use 32,000 m^3 of ammonia fuel, which is a lot…
            But that’s just a rough estimate. Since ships often use crude oil, the estimate may be off.

            [1] https://finance.yahoo.com/news/many-gallons-fuel-does-container-142703880.html

    1. Yes, burning ammonia makes NOx. Lots of NOx.
      This is already a problem with current diesel engines with SCR. With a cold SCR it is possible for ammonia to circulate through the EGR, making NOx, making more ammonia in the cold exhaust….
      NOx is made in diesel engines, but requires temperatures and pressures high enough to make Nitrogen radicals from N2.
      If you are burning ammonia then _every_ Nitrogen atom is a radical part-way through the combustion cycle.
      It might be possible to tweak the stoichiometry so that there is only enough O2 to oxidise the hydrogen, but that only partially works in Diesel engines, so would almost certainly not be a 100% solution with ammonia fuel either.
      Maybe something can be done with exhaust aftertreatment. But that is already massively costly with engines that make NOx in relatively small quantities as a by-product.
      Would the cargo ships of the world keep their AdBlu tanks topped up? It seems unlikely.

      Or maybe we don’t care about NOx out of sight of land? This might actually be the case. It is fairly short-lived (compared to CO2) and the density of ships in the ocean is relatively low compared to city traffic. I don’t think that the Albatrosses would like it though. Having sailed across the Pacific it can be days between sighting a ship, but there was always an albatross visible somewhere.

      1. Because of the NOx problem the best solution is to use a fuel cell – do not “burn” the ammonia. The shipping industry knows this … it is just harder to get up to speed with the tech

  2. I remember cleaning out a valve when I was an anhydrous ammonia operator. Just a few drops escaping, quickly boiling away, and the smell of ammonia was in the shop. I had ambitions for a home refrigeration system with ammonia, but soon learned why we don’t do it…

  3. >diesel which has twice the energy density of ammonia

    Almost any hydrocarbon fuel has more than twice the energy density of ammonia. Ammonia is produced by converting methane gas for a source of hydrogen – natural or man-made – and it would be far smarter to convert that methane up into heavier hydrocarbons like ethane, butane, propane… or their alcohols ethanol, butanol, propanol… which are liquids at room temperature and far less toxic when they leak.

    1. I personally think converting methane to ethane makes a lot of sense in the transport industry.

      Unlike methane that needs to be compressed to about 12 MPa for it to store only 96 kg/m^3, ethane can be compressed to a much lower 4.2 MPa for it to store about 360 kg/m^3. (it is liquid at this pressure at ambient temps, and even increasing temps to 40C only somewhat increase the needed pressure to keep it as a liquid. (ie, we don’t get close to 12 MPa + safety factor.))

      Ethane is though a bit less energy dense at only 50 MJ/kg, compared to methane at 55MJ/kg.
      But considering the whole storage solution, we get about 18 GJ/m^3 for ethane, and methane only reaches 5.3 GJ/m^3.

      Some people say hydrogen is the future though… But needing about 70 MPa of pressure to only store 40 kg/m^3, and at 90 MPa it only increases to 46.8 kg/m^3. Hydrogen is though storing about 100 MJ/kg, but even at 90 MPa it doesn’t beat the energy density of methane… And constructing a tank storing potentially tens to hundreds of cubic meters of gas at these pressures isn’t a simple task in itself.

      Of course one should also consider the larger system, hydrogen is a lot easier to run fuel cells with, that can have efficiencies around 60-80%.
      While ethane is a bit harder for such, but a good ICE still reaches 35-45% efficiency before we add on waste heat capturing to drive a sterling engine or low pressure turbine. (on a ship or power plant, there is more room for this, in a car/truck there kind of isn’t.)

      Ethane also has the advantage that it still has potential for more efficient fuel cells unlike even heavier hydrocarbons.
      And the conversion from methane isn’t having abhorrent efficiency even a few years back, making it attractable as well. (power plants on land should though stick to methane.)

      And methane is already a byproduct that exist in ample amounts. Be it from landfills, or just sewage treatment facilities, compost piles, among other areas. In short, methane is a byproduct humanity will have long into the future and converting it to ethane for transport is fairly logical.

      1. SOFCs are internally reforming – they can burn ethane directly while PEM fuel cells needs straight up hydrogen because they get poisoned by carbon monoxide. SOFCs can directly burn any hydrocarbon fuel that you can turn into a gas – even plain carbon when it’s hot enough.

          1. It’s the inverse of a PEM. Instead of passing hydrogen ions (protons), it passes oxygen ions through a ceramic barrier. Positive instead of negative charge carriers. This is why it’s able to burn carbon.

            The main challenges are making a catalyst that works at a low-enough temperature to afford the use of cheap materials like steel and aluminum instead of special high temperature metals for the catalyst matrix. Otherwise the efficiency is just as good, and you get high grade heat as a side effect which means the waste heat is useful either as-is, or in a combined cycle generator which greatly improves the efficiency.

          1. If you run it on methane, ethane, or other lighter hydrocarbons, then sulfur shouldn’t exist in any noticeable quantities. Especially if the source for the methane/ethane is biogas production.

            If one runs it on diesel, then yes, sulfur exists in plenty. (unless it is biodiesel, that doesn’t really contain much to speak of. But it is more expensive.)

    2. If butanol could run people’s old fashioned ICE cars, be pumped and hauled with existing infrastructure and be used in fuel cell cars, we’re ready to go when we solve the cost issue.

  4. Hm. Wasn’t there an issue with NOx either? Replace CO2 by NOx and be also busted…
    And with even higher energy density, Hydrazine (N2H4) being super toxic? Maybe mankind needs to rethink completely what “burning fuel to produce kinetic energy” really means.

    1. An advantage of ammonia (though I still think it’s not suited as fuel) is that it’s also a reducing agent for NOx, so you could atomize some of it in the exhaust system for more efficient catalytic conversion. No more need for a separate urea tank.

  5. Interesting, but most of the research we have seen is the use of Hydrogen as the alternative fuel. Yes, hydrogen has its issues such as storage and transport, but these are easier to manage on a large vessel (LNG tankers have been transporting and been partly fueled by cryo-gas fuels for years), however it is totally clean, easy to produce and has a good power density. Connect that to a fuel-electric hybrid and you have the perfect green fuel

  6. Seems like a really bad choice for an industry that ignores maintenance at almost all cost.

    Do I think it could be done relatively safely? Yes. Do I think the shipping industry as a whole could do so? Not a chance. Not even close. Within 5 years there’ll be more ghost ships in the ocean than in our entire past history. (All crew dead)

    Maybe chlorine gas could be used as a fuel instead? (This is a joke)

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