Plants are naturally “solar powered,” but there is a carbon footprint associated with growing them as a crop. The fuel used to power tractors and other equipment is part of that footprint, but the largest component on the order of 36% is associated with the natural gas used to make synthetic nitrogen fertilizers.
Between conflict-driven disruptions in the global natural gas market and the urgent need to address climate change, nitrogen fertilizer’s dependency on fossil fuel is becoming untenable. The ideal solution would be to find a way to make a low carbon footprint supply of nitrogen using local, renewable energy. Is that possible? In this case the answer may be literally be “blowin in the wind.”
Green plants get the energy to grow from the sun through the process of photosynthesis. They do; however, need nutrients – minerals that they absorb from the soil through their roots. Nitrogen, Phosphorus and Potassium are the plant’s greatest needs and in agriculture or gardening those are supplied as fertilizers. Throughout human history, nitrogen was the most limiting element for crop production, and as population increased the available nitrogen sources such as domestic animal manure or bird guano could not supply all that was needed. The challenge of getting enough nitrogen for plants is somewhat ironic because the atmosphere contains 78% nitrogen gas; however, it is quite inert and unavailable to most living things. Just over 100 years ago the fertilizer situation changed. A German scientist named Fritz Haber came up with a catalyst and pressure system to use hydrogen and some of the nitrogen in the air and turn it into ammonia which is a form available to plants. Another engineer named Carl Bosch perfected and scaled-up the process so that by 1914 it was possible to produce 20 tons/day of usable nitrogen.
This “Haber-Bosch” process is optimally performed in large scale facilities each producing on the order of 1 million tons per year either from natural gas sources or through coal gasification. Natural gas is composed of one carbon and four hydrogen atoms, but it is only the hydrogen that is needed to react with nitrogen in the air to make ammonia (one N atom with three hydrogen atoms). The carbon in that case is from a “fossil” source so it constitutes a “greenhouse gas emission.” There is a different way to generate hydrogen called electrolysis. All that is needed is some water (two hydrogen atoms and one oxygen atom) and electricity. This process splits off the hydrogen and releases the harmless oxygen. In this scenario there is no carbon emission. Public and private researchers have been experimenting with small-scale Haber-Bosch processes to make ammonia. The focus has been on using wind- or solar-generated electricity. This concept has been in the works for some time. For instance in 2009 a $3.75 million pilot plant for at the University of Minnesota’s West Central Research and Outreach Center was using electricity from a local wind power facility to produce 25 tons of anhydrous ammonia per year. This was described in an interview with Mike Reese, the Renewable Energy Director at that Minnesota facility published in the agricultural trade journal Corn+Soybean Digest. The article was aptly titled: “Make Fertilizer From Thin Air? Using Stranded Wind Power to Make Renewable Ammonia Could Stabilize N Prices, Build Wind-Power Markets.”
So what is happening 13 years later? As with any new chemical process it takes time for optimization. There are also economies of scale that make it difficult to compete with a well established, industrial-scale process like that used for modern fertilizer production. However it is possible that versions of this technology are approaching a commercial feasibility. A “Techno-Economic Analysis” published in 2020 by researchers at Texas Tech concluded that “all electric” ammonia could be produced at about twice the cost of conventional commodity ammonia. That was before the dramatic increases seen with fertilizer prices for the 2022 growing season (see Modern Farmer: “Farmers Struggle to Keep Up With Rising Fertilizer Prices).
In an interview for this article Mike Reese from the University of Minnesota facility says that momentum is building for this solution. With natural gas cost rising, renewable electricity costs dropping and commitments to climate change mitigation coming to the forefront; there is now broad interest in this sort of “green ammonia” option. Reese says that several of the large-scale, conventional fertilizer companies are looking into how they might shift in this direction. Reese’s description of this technology is posted on the center’s website: “Fueling Sustainable Energy and Agriculture: Putting Wind in a Bottle.” UMN researchers have also published a related economic analysis.
A logical scenario is to develop medium-scale plants in the 30 to 200 ton/year range and locate them throughout agricultural regions where there is plenty of potential for wind and solar electricity generation. That way the transportation footprint of the fertilizer would be small and the market would be insulated from global price swings. Obviously there would be the need for substantial capital investment, but that might be partially addressed through climate change-driven subsidies or through carbon credits. This change would also be positive for the solar and wind energy sector because it addresses their need for utilization during peak production periods that might not line up with grid demand. There is an independent line of interest in ammonia as a safer means of storing hydrogen for later release for many different applications.
As if this story wasn’t already positive enough, there is a way that fertilizer production could be even further “decarbonized.” There are bioethanol plants spread throughout many US farming regions. When they are fermenting the carbohydrates of from feed stocks like corn starch they emit CO2, but it is “carbon neutral” in that it comes from recent crop photosynthesis. However, it is possible to capture that abundant supply of gas and react it with ammonia to produce urea which is a more easily stored and applied form of nitrogen fertilizer and one that can be converted to other common formulations such as UAN or slow-release pellets. Making this link between ammonia and ethanol production would have both business and logistical advantages in addition to the carbon footprint reductions associated with each product.
In conclusion, electrification of ammonia production for agriculture appears to be an excellent example of the sort of solution envisioned by “ecomodernists” who argue that technology is often the solution to environmental challenges. In this case that also aligns with a need to protect our farm economy from global instability.
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