By: Kyle Antonini
There has been much ado about the transition to alternative forms of fuel in the maritime industry as emissions standards become more stringent, climate change due to greenhouse gases becomes more real, and current “clean” options become more expensive. Since the industry is huge and financially conservative, it is difficult to see widespread change without sweeping regulations or publicly visible catastrophes (the Hindenburg effect).
Changes in emissions standards forced two technological developments that have seen more widespread adoption in recent years. One is the use of scrubbers and other such technologies that work to rid exhaust gases of some of their harmful chemical byproducts. The other is the transition to LNG as the main fuel source in place of heavy fuel oils. LNG is a fairly clean alternative (when compared to fuel oil), but its combustion still emits greenhouse gases (only 23% reduction from fuel oil), and, arguably, issues like methane slip can be far more detrimental to atmospheric heat retention than carbon dioxide.
Drastic reductions in greenhouse emissions can only be achieved if we can wean ourselves off hydrocarbons. There has been practical progress in the development of another very common chemical that can be used effectively in existing internal combustion processes and produces no greenhouse gases (instead just outputting air and water); Ammonia. Ammonia (NH3) can also have far-reaching energy storage and transport implications as more efficient means of manufacturing are commercialized and scaled up.
Ammonia is already produced in large quantities for fertilizer applications, and it is our most widely used non-hydrocarbon commercial chemical. It is known to be a highly effective refrigerant, but is also widely considered toxic and in need of special handling. However, other widely used hydrocarbon fuels are toxic and require special handling as well. IMO has already issued new training requirements for engineering crews onboard LNG vessels [LINK], because working with any low-flashpoint fuels is inherently dangerous. Thus, the perceived dangers should not stop us from looking at the benefits.
Ammonia is a gas at room temperature, but it can be stored as a liquid at room temperature at a pressure of only about 10 atmospheres. Alternatively, its boiling point at atmospheric pressure is -28 F. This is much more easily attainable compared to LNG, which requires storage at -260 F at atmospheric pressure.
One difficulty that can make ammonia less effective as a fuel is that it does not combust as readily and at as low a temperature as other internal combustion fuels. This problem was solved by creating mixtures of existing hydrocarbon fuels and ammonia. The combustion of the hydrocarbons helps the ammonia along with its own combustion, and then the engine cycle works as per usual. The result is a slightly less efficient engine (the energy density of ammonia is less than that of fuel oil or LNG), but the reduction in greenhouse emissions becomes roughly proportional to the proportion of ammonia in the fuel mixture. The NH3 car effectively demonstrated this on a small scale by successfully driving cross-country with a mixture of fuels. (Props to my alma mater.)
Realistically, the transition to ammonia mixtures for ship fuel can seem like a nuisance, because now ships would need to refuel with two different types of fuel every time they take on bunkers, but, at the same time, recently many ships have been bunkering three types of fuel (Diesel, HFO and low sulfur HFO). Considering the outfitting that needs to occur for new LNG fuel tanks (a nuisance that people are willing to live with), the nuisance of adding ammonia to our fuel tanks doesn’t seem too farfetched. LNG lacks a lot of the transport and supply infrastructure of other fuels, but ammonia already has a lot of infrastructure in place thanks to its agricultural applications.
The current process for mass-manufacturing ammonia, the Haber-Bosch Process, uses natural gas as a hydrogen source, and thus the overall systematic efficiency and environmental benefit of ammonia usage is stymied by this input. That may stop the ammonia conversation right there. However, experimental methods of sustainable production from just water and air are being seriously considered. Once these processes can be commercially adopted on a mass scale, the future of ammonia fuel becomes a much brighter one.