Review on Ammonia as a Potential Fuel: From Synthesis to Economics

Abstract

Ammonia, a molecule that is gaining more interest as a fueling vector, has been considered as a candidate to power transport, produce energy, and support heating applications for decades. However, the particular characteristics of the molecule always made it a chemical with low, if any, benefit once compared to conventional fossil fuels. Still, the current need to decarbonize our economy makes the search of new methods crucial to use chemicals, such as ammonia, that can be produced and employed without incurring in the emission of carbon oxides. Therefore, current efforts in this field are leading scientists, industries, and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis, this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector, moving through all of the steps in the production, distribution, utilization, safety, legal considerations, and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed, thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works, this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further, the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes, legal barriers that will be faced to achieve its deployment, safety and environmental considerations that impose a critical aspect for acceptance and wellbeing, and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein, this work sets the principles, research, practicalities, and future views of a transition toward a future where ammonia will be a major energy player.

The Role of Electrofuels under Uncertainties for the Belgian Energy Transition

“…Given its advantages (e.g., carbon-free hydrogen-carrier, existing infrastructure), this molecule looks to be an attractive solution as an energy-carrier for power applications [67], when used as dual fuel with hydrogen or methane [5,6] or to defossilise the freight transport sector (e.g., maritime transport) [68,69]. However, many challenges remain regarding its synthesis, its uses and applications (i.e., in a combustion engine or in a fuel cell), or even its environmental impact [70]. These questions make the use of ammonia as a fuel, such as the emerging technologies, still very uncertain.…”

Operating Limits for Ammonia Fuel Spark-Ignition Engine

“…However, even using the best available technologies, its density is too low for it to be easily transported and stored with acceptable safety and at a reasonable cost. Among other renewable fuels, Ammonia (NH 3 ) is currently receiving an increased interest as a potential renewable carbon-free energy carrier [1][2][3]. It is both considered as a fuel for direct use in a combustion system or fuel cell, or as an efficient hydrogen carrier (17.8% hydrogen content by mass) when it is decomposed.…”

“…Although ammonia use as an internal combustion engine fuel has been considered since many decades, its deployment was first limited by the competition with hydrocarbon fuels in terms of availability, handling ease, and safety, as well as energy density and combustion properties. Indeed, it is a toxic chemical with difficult flammability and very low combustion intensity, illustrated by its narrow flammability limits (FL) and low Laminar Burning Velocity (LBV) in Table 1 ((data from [2,4,5], respectively. Nonetheless, today's context on global warming is making fossil fuels undesired due to their unacceptable environmental impact, and ammonia exhibits many advantages.…”

Sustainable Biological Ammonia Production towards a Carbon-Free Society

“…Therefore, to improve this situation, Sustainable Development Goals have been declared, and not only researchers but also governments and corporations of various countries are taking great interest in improving the global environment [1,2]. Furthermore, to achieve a carbon-free society, we should reduce our dependence on fossil fuels for energy production and increase the use of renewable resources, such as geothermal, hydro, solar, and wind power [3][4][5][6]. Interestingly, wind-power generation has recently received the most attention and wind turbine generators are spreading greatly [7].…”

“…Therefore, the synthesis of primary amines from ammonia contributes to produce important key chemicals for manufacturing dyes, pesticides, and pharmaceuticals in the chemical industry [12][13][14][15][16][17]. Ammonia is also expected to be used as fuel [6,8,[18][19][20][21][22][23], as 1 mol of ammonia contains 1.5 mol of hydrogen. Thus, due to its high volumetric hydrogen (121 kg m −3 ) and weight fractions (17.8 wt%), ammonia should be used as an efficient carrier of hydrogen.…”