Introduction
Ammonia has been used as a fuel in certain applications, such as to power buses in Belgium during World War II and to power the X15 rocket airplane that set speed and altitude records in the early 1960s. Recently, ammonia has been proposed by some as an alternative to fossil fuels for internal combustion engines for stationary generator and vehicle applications. Most ammonia used in the world is produced by converting natural gas into hydrogen through steam reformation and then using nitrogen from the air to make ammonia through the Haber-Bosch process. This process pulls nitrogen from the air and fixes it to hydrogen in a reactor to create ammonia. A iron oxide catalyst in a high temperature and pressure environment is used to strip the nitrogen molecules and bind them with hydrogen. This process is generally only 15% effective, although the unfixed elements can be recycled and ran through the reactor again1.
Fertilizer made from ammonia
Image: agmrc.com
Ammonia as an Alternative Fuel
Ammonia is preferable to hydrogen in terms of energy storage due to the fact that it remains a liquid when stored under modest pressure, but it has approximately half the energy density of diesel. This means it requires twice the storage volume to achieve the same energy content. Nonetheless, ammonia is a viable alternative and it can run in most existing engines with only minor modifications to carburetors and injectors. Ammonia as fuel has no serious problems associated with it in terms of toxicity, flammability (ammonia is not considered flammable due to its high auto-ignition temperature), or emissions (although it does have a distinct odor). It is widely produced and distributed, although transporting ammonia over long distances would not be economical due to its lower energy content per pound. However, ammonia has been researched as a way to transfer hydrogen due to its ability to be liquified under relatively mild conditions and high capacity for hydrogen storage2 . About 80% or more of the ammonia produced is used for fertilizing agricultural crops.
Ammonia in Alaska
The Agrium fertilizer plant on the Kenai Peninsula produced 280,000 tons of ammonia fertilizer annually from a natural gas feedstock and shipped the product to many countries across the globe. The plant shut down in 2007 due to the inability of securing a natural gas supply in Cook Inlet.
Manufacturing ammonia onsite in rural Alaska is a possibility using the Haber-Bosch process. It could be manufactured from renewable energy sources included stranded hydro resources using an air separation plant to collect nitrogen (air is composed of 78% nitrogen), and an electrolyzer to generate hydrogen from water. In contrast to using the hydrogen directly, converting the hydrogen to ammonia eliminates the need for high pressure compression, as ammonia can be stored and transported as a liquid at reasonable pressures. This means that existing infrastructure could be used for handling, storing, and transporting without the need for exotic storage material. In addition, industry standards and regulations exist for the safe handling and storage of ammonia.
Based on the expected capital cost of the equipment, ammonia would not become economic to use as a fuel until the cost of diesel reached $10.45 per gallon (see analysis). This is an optimistic analysis based on commercial production of 4.5 Mmbbl per year and no electricity cost. A more realistic analysis calculated a break-even equivalent value of diesel fuel at $13.50.
Since diesel is not expected to reach this value, even in rural Alaska in the near future, this option does not appear economically viable unless the equipment cost (electrolyzer and air separation plant) is reduced significantly.
Links, Resources and Documents
The Energy Collective: An opinion piece about ammonia as an alternative fuel. Contains a brief look at all the aspects of using ammonia as economically reasonable fuel source.
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