A Roadmap to the Ammonia Economy?

05.11.20 | Blog | By:

Researchers at Monash University in Australia have proposed a roadmap to renewable ammonia being produced in the future at a scale that is significant in terms of global fossil fuel use in a paper recently published in Joule. The authors note that while there is global potential to generate renewable energy at costs already competitive with fossil fuels, a means of storing and transporting this energy at a very large scale is a roadblock to large-scale investment, development and deployment.

Ammonia produced from renewables can be a viable liquid fuel replacement for many current-day uses of fossil fuels, including as a shipping bunker fuel; as a diesel substitute in transportation; as a replacement fuel in power turbines; and even as a potential jet fuel. The global transportation of ammonia by pipeline and bulk carrier is already a well-developed technology. The figure below presents the authors’ vision of the “ammonia economy”.

Vision of the ‘‘Ammonia Economy’’ in which the Energy Sources and Uses Are All Based on Ammonia

MacFarlane et al., A Roadmap to the Ammonia Economy, Joule (2020), https://doi.org/10.1016/ j.joule.2020.04.004

The authors note ammonia is readily liquefied by increasing pressure to ~10 bar at room temperature, or by cooling to −33°C at atmospheric pressure. Unlike liquid hydrogen, the technology of shipping and pipeline transfer of ammonia is well established in the existing industry. Approximately 175 million tons are produced annually worldwide, for a market of value around USD 70 billion; by comparison, the global liquefied petroleum gas (LPG) market is around 300 million tons annually. Most of this ammonia is used in the production of fertilizers, with small amounts going into explosives and chemicals and materials.

The authors note that just over a century ago, the discoveries by Haber and Bosch (H-B) made possible the industrial production of ammonia and ammonia-based fertilizers that today feed the world and are the source of most of the nitrogen-containing chemicals, materials, and pharmaceuticals. Ammonia production is currently responsible for ~1.0% of global greenhouse gas emissions (or about 1.4% of global CO2 emissions); these values increase further if CO2 emissions associated with natural gas extraction are included. Over the last decade, momentum has been building to transform the Haber-Bosch (H-B) ammonia industry toward renewable sources of hydrogen, for example, from water electrolysis or solar thermal cycles, but authors note economics is the big challenge.

In the paper, the authors suggest a roadmap to scale up renewable ammonia. The paper goes into much greater detail, but here is brief summary of their approach:

  • Generation 1: This involves the use of carbon sequestration or offsets to bring the net carbon impact of the ammonia production to zero (blue ammonia). Carbon sequestration adds cost and plant complexity on top of the existing H-B technology. For this reason, the researchers said, it is likely to represent only a transitional solution, helping to establish a market for ammonia beyond the fertilizer and chemical industries. Modern H-B plants produce ammonia at an energy cost of at least 8 MWh tonne-1. Recognizing that the lower heating value (LHV) of ammonia is 5.2 MWh tonne-1, this represents an energy efficiency of only 65%.
  • Generation 2: This involves renewable ammonia is produced from H-B technology but employs renewable, rather than fossil-fuel-sourced, hydrogen. This has the advantage that existing H-B plants can be transitioned to this new hydrogen supply without major disruption or mothballing. Powered by fully renewable electricity derived from a 20 kW wind turbine, a Siemens demonstrator produces H2, using a proton exchange membrane (PEM) water electrolyzer, to form around 30 kg NH3.

Gen 2 technology has significant long-term scope in terms of the ammonia economy, limited only by the substantial investment and long lead time required to establish new facilities.

  • Generation 3: This technology is based on the electroreduction of N2 to ammonia by direct or mediated means. The H-B process is no longer required; instead, the reaction is driven by electrochemical reduction and the H source is water.

    MacFarlane et al., A Roadmap to the Ammonia Economy, Joule (2020), https://doi.org/10.1016/ j.joule.2020.04.004

The timeline and scale up under the authors’ roadmap is shown to the right.

As the focus on ammonia as a liquid energy carrier has developed in recent years, so also has investigation of an increasingly broad range of applications, the authors note. In the last few years, the vision of ammonia energy applications has been widening significantly to now include its direct use as a fuel, especially for shipping. For example, recent work by UMAS and Lloyd’s Register has touted ammonia as the best option to decarbonize shipping. Ammonia as a diesel substitute for heavy-duty vehicles and for jet engines has also been suggested. The paper also mentions ammonia as a potential fuel for internal combustion engine vehicles (ICEVs) and references studies that have been done on this in South Korea and also by Toyota. It also mentions ammonia as a component of both solid oxide and direct ammonia fuel cells.

The authors note as part of their conclusion:

“Ammonia clearly has the potential to become the dominant form of transportable renewable energy in the future, displacing fossil fuels from all but the most demanding of applications. It will sit alongside other forms of chemical energy storage, including hydrogen and renewable carbon-derived fuels, as well as battery storage for grid and local electrical energy storage, as one of the core components of renewable energy technology. In some contexts, for example buses, several of these technologies will compete with one another at the local level, but the important distinguishing feature of ammonia is its well-established ease of global transportation, by bulk carrier and pipeline. This opens up the most promising high-yield regions of the world in terms of renewable energy generation, both on- and offshore, to global markets.”

 

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