Thermoeconomic evaluation of a novel small-scale Power-to-Ammonia concept

The quest for sustainability requires all branches of the economy to become more renewable. In the energy sector, this means switching to renewable primary energy sources, such that the derived energy carriers and their end usage are renewable as well. The molecule ammonia, consisting of one nitrogen and three hydrogen atoms, has the potential to be such a renewable energy carrier. For most of the past 100 years, ammonia has solely been regarded as a fertilizer, with the required nitrogen extracted from the air being fixed to hydrogen. Nowadays, the other purpose of ammonia emerges, i.e. the fixation of the highly volatile energy carrier hydrogen to nitrogen. This work proposes a novel small-scale, Haber-Bosch based, Power-to-Ammonia process. Its simple design aims to produce ammonia from water and air using renewable electricity – in a low temperature and low pressure regime, under changing operating conditions, safe and cost superior to a more conventional concept. The use case of such a containerized process are remote farming areas, where farmers strive for fuel and fertilizer independency. The four publications that make up this cumulative thesis are part of the fundamental steps of the process design workflow of the novel concept: A steady state thermodynamic and a dynamic evaluation of the concept, followed by a comparative investigation regarding exergy and exergy-costing between the novel concept and a more conventional one. The results suggest that the novel design has the potential to deliver on its promises, namely producing ammonia at low pressure and temperature, dynamically and safe as well as exergy-cost superior to the competing conventional concept. However, the extensive critical analysis of the four publications conducted in this work also points out its weaknesses, mostly the many simplifying assumptions that had to be made for the simulations. Nevertheless, ways to eliminate these weaknesses in the future are suggested in this work as well. However, in the end, only the still pending commissioning of the containerized concept will reveal how far the promising results of the publications are in agreement with reality.