Exergetic comparison of a novel to a conventional small-scale power-to-ammonia cycle

Green ammonia is a promising carbon-free energy vector and means to store hydrogen efficiently. Employing the software Aspen Plus®, this work presents an exergetic comparison of a novel small-scale power-to-ammonia system, to be tested in 2023 and designed for low investment cost and dynamic flexibility, to a conventional system. For a thorough evaluation six equations of state, one provided by an industry partner, as well as chemical exergies with and without excess values are compared. With 64.59%, the novel design has a 4.87% lower exergetic degree of efficiency. The difference can be attributed to the simplified design of the novel cycle, mainly to the use of an electrical preheater instead of an internal gas-gas heat exchanger and a recycle valve instead of a recycle compressor. However, an upcoming exergy economic analysis will show that the novel cycle is more economical overall, as its investment costs are lower.