Techno-economic analysis of a solar ammonia and fertilizer production

Abstract

Due to rapid climate change, society and politics pushes the fertiliser industry to decarbonise and reduce its emissions, as it is responsible for 1.4% of annual CO2 emissions. To avoid this environmental problematic, research and development in the chemical industry is currently focused on the search for the production of green ammonia and its integration into the production of nitric acid. This work aims to contribute to the quest of new sustainable processes that help the decarbonisation of the fertiliser industry. The MSc thesis focus on the search of synergies between solar­powered nitrogen and hydrogen production technologies to provide green ammonia, and the subsequent nitric acid process. Specific attention is put on the effect of utilizing the oxygen by­product from solar­powered thermochemical air separation to produce nitrogen, and from water splitting to provide green hydrogen. A tecno­economic evaluation is performed for three different types of nitric acid plants: a conventional nitric plant (CONV­NA), i.e using fossil­based ammonia, a solar­based ammonia to nitric acid plant (SOL­NA) and a optimised solar­based ammonia to nitric acid plant (OXY­SOL­NA), in which surplus oxygen from green ammonia production is injected into SOL­NA. All the plants are simulated in Aspen Plus® and their economic analysis is performed by following the methodology of the book entitled: Plant Design and Economics for Chemical Engineers. A reference case of a mono­pressure nitric acid production process is simulated for a plant capacity of 700 t/d (eq. 100%) at a concentration of 60 wt% (CONV­NA). The investigations of injecting pure oxygen at four different points of the plant show that daily nitric acid production can be boosted by 0.34% and final NOx concentration of the absorption column can be reduced by up to 43.6% by enriching the main air pipeline with oxygen. The capital costs for the OXY­SOL­NA plant are reduced by 0.65 Me compared to the CONV­NA and SOL­NA plants. Nevertheless, the operating costs end up being more relevant in the final cash flow analysis. The CONV­NA plant has 17% lower operating costs compared to the two green ammonia plants which is explained by the fact that ammonia costs accounted for 52.65% of the total operating costs. For that reason, CONV­NA plant has an end­product price 14% lower than the other plants. Regardless of environmental considerations, such a significant difference in the final price may make your product unable to compete with other potential competitors. Currently, green ammonia is mainly dependent on the price of green hydrogen production due to the high LCOE for solar energy and the lack of maturity of water splitting technologies. CO2 pricing policies could make the implementation of green NH3 in the nitric acid production process feasible in the near future.