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Monday, April 1, 2013

Moving Towards Fossil-Energy-Independent Nitrogen Fertilizer


It takes about as much energy to make the nitrogen fertilizer for an acre of corn (150 lbs) as it takes to drive a car 600 miles, and because it is made using natural gas it has a carbon footprint equivalent to driving the car 650 miles.  Now imagine that for more than 90 million acres of corn.  That is a lot of energy.  But what if that energy and greenhouse gas footprint could disappear?  This might actually be possible.  

By way of background, nitrogen is one of the three most important minerals that plants need to grow, and the basis of the protein we require in our diets.  Some plants call legumes “fix” their own nitrogen with the help through a mutualistic relationship with a particular kind of bacteria.  From an environmental point of view, this sort of  biological nitrogen fixation is the best way to make nitrogen fertilizer.   US farmers already plant about 100 million acres of legume crops (soybeans, alfalfa...).  We could probably supply a fair amount of additional nitrogen if legume-containing winter cover crop mixes were more broadly used.  Still, to grow our conventional crops like corn, wheat, barley, fruits, most vegetables.... we need to make synthetic nitrogen.  Even organic is dependent on that flow (see previous post, Cows Don’t Make Fertilizer).

Large scale, crop-available nitrogen production became possible about 100 years ago when two German scientists named Haber and Bosch sequentially figured out how to turn the nearly 80% nitrogen in the atmosphere into plant available forms.  All it takes is a source of hydrogen, the air, and a catalyst to make ammonia. They got a Nobel Prize for this, but the big down-side has been that the most cost effective way to do the Haber-Bosch process has been to get the hydrogen from natural gas.  The question is whether there is an alternative to this major use of a fossil fuel (~5% of total natural gas use).

The Answer My Friend, Is Blowin' In The Wind


Bob Dylan was famously vague about what "the answer" actually was, but I'm guessing that he wasn't thinking about a solution to the fossil fuel dependency of crop fertilizers.  Even so, his reference to wind may actually be part of the answer to this real-world dilemma.   The Haber-Bosch process just requires hydrogen and that can easily be made using electricity and water (electrolysis).  The electricity could be from a renewable source like wind, solar, hydro etc.  I once wrote a blog post wondering if it might be possible for someone to develop a small-scale Haber-Bosch process that could be run using something like wind energy.  It turns out that at least three groups were already working on different approaches to just such an invention ( University of Minnesota, Electrogen HydrofuelsAltmerge).  I am really excited about this possibility, particularly the later two because they are working on very small scale units.  For instance the one from Electrogen is designed to fit in a standard truck/rail container.

If any of these processes can be successfully commercialized, it could dramatically alter the fertilizer paradigm.  It would give farmers a way to locally and independently produce their own fertilizer and thus avoid the price fluctuations driven by the general energy market.  A farm could install a wind turbine and one of these units and let it make the next season’s fertilizer any day that the wind blew.  These companies are also working on ways to turn the ammonia generated into something easier to store like liquid ammonium nitrate (not the dry form that can be turned into a bomb).  

Such a system might also be able to provide village-level fertilizer generation in parts of the world where small-holder farmers don't have practical access to nitrogen fertilizer today.  

This nitrogen fertilizer would be "carbon neutral" from a manufacturing perspective.  Since the energy used to make fertilizer is a large part of the overall carbon footprint of agriculture (about 40% for a corn crop), this change would be highly significant.  Nitrogen fertilizers will still always have other environmental issues, but there are sustainable soil health management systems that best address those.

The irony is that this sort of carbon-neutral nitrogen fertilizer wouldn't qualify under the current rules for use in organic because it would still be “synthetic.”  Of course plants don’t care about this.  They can only absorb nitrogen in its nitrate or ammonium ion form which is the same whether it originated as synthetic or natural fertilizer.  

Wind turbine image from SustainableDevelopment's photostream

You are welcome to comment here and/or to email me at savage.sd@gmail.com

14 comments:

  1. There's also solid state ammonia synthesis (SSAS), currently at demonstration scale using stranded wind in Alaska

    http://www.akenergyauthority.org/EmergingEnergyTechologyFund/EETF-AC_Stage1_Review/Abstracts/001.pdf

    and claiming considerably better efficiencies than other methods.

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  2. Good post on an important topic. Thank you! However, I doubt that small scale units make economic sense. Farmers today could produce their fertilizers with their own small Haber-Bosch processes, but still prefer to buy the fertilizers from someone else. Small scale wind is costly and has typically much lower capacity factors than large turbines and even those are uncompetitive without subsidies. Industrial plants prefer/need reliable power sources and if it is carbon free you want that will in the end be nuclear power or something like wind coupled to large amounts of storage...which is very costly. I am a fan of co2 free fertilizers and probably the best way to get them is to use nuclear power (at night for example) to produce hydrogen. That way you get much more output from the same infrastructure. Try to get organic certificate for that :-)

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    1. Yes, economics will determine it, but early projections are better than one might think. There would be other options as well such as using the methane from an anaerobic digester to generate the electricity and hydro for those who have such an option. Small nuclear sounds good too

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  3. New Holland has been showing a hydrogen fuel cell tractor for several years now. I recently read New Holland's ultimate goal is to be able to supply farmers with a wind turbine that produce the fuel for their hydrogen powered tractors. As a farmer I can assure you if the price of the equipment was right, not buying diesel fuel (one of my top expenses) would be a welcome addition to the farm! Same goes for N.

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    1. Actually, the ammonia can be used to run modified engines as well and it is at least a little less difficult to store. The military is actually looking at this as an alternative to the huge cost of bringing in diesel to a place like Afghanistan

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  4. On my last drive on I-80 from CA to the midwest I saw wind farms everywhere. If this were economically competitive it'd be a real game changer. I think this is the first article I've read that's made me optimistic about the future of ag in months. Thanks Steve!

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  5. Interesting post. Can you elucidate the energetics involved? Of your three links, the University of Minnesota’s was the only one that seemed to have some energy data. By my calculations, which are most likely wrong, their system would produce fertiliser at about 80 MJ per kg nitrogen, assuming a 26% capacity factor – and assuming that the figure they give of 10% of their turbine’s output covers the entire energetic cost of the process. The Alaskan system linked by Luke_UK seems to come out at about 30 MJ per kg nitrogen (7.5 kWh/kg conversion). Does that seem correct? So by my reckoning to generate all the fertiliser currently used in the US using the Minnesota method would require about double current installed (presumably grid-based) wind power (of 60,000MW) for fertiliser manufacture, or about 5% of total US energy demand? Not an argument against your proposal, but a context for it.

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  6. Chris,
    Good points, and I'm sure the entire capital investment/energy balance calculation needs to be done. One of the arguments for this is that wind power is quite feasible in agricultural areas, but to connect it to the grid is both expensive and also involves transmission losses. With that and other renewables there can be a necessary over-investment because it is hard to match the timing of generation with the timing of demand. What is appealing to me is that for many situations the calculation on this would just be based on how the capital and operating cost of each unit made the cost/pound N compare with market prices. For now, natural gas will be cheap so it will make the calculation challenging; however, the small scale unit I know the most about has the ability to utilize the energy released in the main Haber-Bosch reaction to power another step whereas on the large scale it is lost as heat.

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  7. That's a great post! I really enjoyed it.

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  8. I think the best aspect of this is the current fertilizer plants would just have to replace the natural gas cracker at the front of their line with an electrolysis machine to convert the factory to carbon-nuetral.

    Such a plant could make use of cheap surplus power from a grid with lots of renewable energy sources, allowing electrical demand to track the varying supply. We could also have hybrid fertilizer plants where they use electricity when it's cheap, and natural gas when it's expensive to allow continuous low cost production.

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  9. I predict another evolution of this knowledge.
    The rich industrialized countries will produce more and more because of their cheap fertilizers (= kind of energy production). So they can continue to waste energy.
    What about the climate? It is not a solution, only postponing the problem.
    We are changing the biosphere by moving the nitrogen to another sink=level.
    What will be the consequences on long term? Why do we need more crops? What will we do?
    Our subsidising production on a large scale and buying up surpluses in the interests of the market is given us problems yet! Not only in our own countries but also abroad!
    By dumping the surpluses on the market of Mexico(US) or Africa (EU)we kill the development of the native agriculture and...become richer! Is that the goal of this invention?
    We must learn not to be so greedy and realize we are devastating our environment because of our blind arrogance. This is more dangerous than the atomic bomb.

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    1. Anonymous,
      Although there are real environmental issues with nitrogen load, producing it without fossil carbon is still a good idea. The prevention of nitrate loads in surface water is best addressed through no-till farming and the use of cover crops. Those same methods keep soils better aerated so that nitrous oxide emissions are minimized. If municipal water treatment plants could be modified to recapture N and P it would be great. Nitrogen has a cycle much like water and eventually ends up back in the 80% in the atmosphere as N2.

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  10. Hi, I like your post. As per your details for this we require large land. I'm awaiting for your small scale unit research.

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