Electrified production of ammonia as chemical product and energy storage

  • Elektrifizierte Produktion von Ammoniak als chemisches Produkt und Energiespeicher

Wang, Ganzhou; Marquardt, Wolfgang (Thesis advisor); Mitsos, Alexander (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik series AVT.PT - Process Systems Engineering 22
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022


The transition towards a climate-neutral economy pushes the one-hundred-year-old ammonia industry to search for sustainable alternatives that reduce the fossil fuel dependency. At the same time, the growing penetration of variable renewable resources amid the Energiewende, driven by strong cost reductions and policy support, is becoming more and more system-relevant and asks for flexibility solutions on the utility scale. Power-to-Ammonia (PtA) technologies provide means to tackle the challenges of the individual sectors jointly. In this dissertation, two enabling process concepts and their potentials are systematically investigated. At first, a highly efficient ammonia-based concept is developed for large-scale energystorage. It utilizes a reversible solid oxide fuel cell for power conversion, coupled with external ammonia synthesis and decomposition processes and a steam power cycle. A refrigeration cycle is utilized to recycle nitrogen and oxygen in alternating mode and hence enables the closed-loop operation of the energy storage. Through heat integration and first-principle model-based optimization, the new energy storage concept demonstrates an electrical round-trip efficiency above 60%. Its levelized cost of storage can be obtained at the same level to that of pumped hydro and compressed air energy storage. Next, a renewable ammonia production process that is suitable for conducting demand side management (DSM) is proposed. A vertical integration of nitric acid production facilitates efficient heat integration between steam electrolysis and the rest of the process. The economic performance of the production complex is investigated through a model-based dynamic optimization approach, considering scenarios with or without incorporation of intermittent wind power as well as deployment of battery storage. In all cases, the wind power integration proves to be economic with a peak-to-base load ratio of up to 2.3. The new process reduces primary energy consumption by more than 13% compared to conventional technologies.Finally, the potential of implementing the PtA process concepts in the German energysystem is analyzed. To identify contributions of individual technologies, a consistent system optimization approach is carried out in a series of scenarios that build upon each other. Compared to a scenario without any PtA technology, the deployment of the proposed ammonia-based energy storage system in the national grid proves essential to limit renewable electricity curtailment and to completely eliminate CO2 emissions in power generation. Adding flexible production of renewable ammonia to the grid helps reduce the need for grid storage. Through actively exploiting power price signals, the CO2 abatement cost for renewable production is lowered by up to a half to below 150€/t CO2. The revenue from offering DSM is also identified to be the key for the domestic ammonia industry in competition with renewable production abroad with abundant renewable resources. Beside chemical product, the value of importing renewable ammonia for energy end-products is investigated. While it is not an economic hydrogen-carrier, ammonia could be more attractive than hydrogen used for power delivery over long distances.