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R. Abdiwe:
"Ammonia as Energy Storage Carrier in CSP Power Plant with Power Tower Receiver";
Supervisor, Reviewer: M. Haider, A. Werner; Institut für Energietechnik und Thermodynamik, 2017.

The actual thesis had the objective of analyzing Power Tower CSP plant with thermochemical storage. To investigate the generation efficiency in the power generation system an exergy analysis on each component of the Central Receiver System (CRS) was conducted. With the exergy analysis it was shown where we should be focusing our efforts to improve system efficiency. EBSILON®Professional software was used in this study to obtain the exergy efficiency and the irreversibility in each component of a hypothetic CRS power plant to pinpoint the causes and locations of the thermodynamic imperfection. The obtained results show that at a constant DNI the maximum exergy loss occurs at the Solar Tower Receiver (STR). The performance of the STR affects significantly the efficiency of the entire solar power generation system and minimizing the heat loss of the STR plays a dominant role in increasing its performance. The simulation tool ANSYS® FLUENT® was used to compare the heat loss in an external type receiver and a cavity type receiver. The result showed that the heat losses in the external receiver are much higher than the heat losses in the cavity receiver making the cavity receiver a better option for increasing the power generation efficiency of the CRS.
Other major challenge is the increase of the system efficiency of the energy storage method. Thermochemical concept seems to offer an attractive solution to this problem. A thermochemical conversion of solar energy into chemical fuels offers an efficient path for long term storage and long-range transport of solar energy. In this study a thermochemical system using ammonia as energy storage carrier is investigated. A transient mathematical model using MATLAB software was developed to predict the behavior of the ammonia closed-loop storage system including but not limited to the ammonia solar reactor and the ammonia synthesis reactor. The MATLAB model contains transient mass and energy balances as well as a chemical equilibrium model for each relevant system component. For the importance of the dissociation and formation processes in the system, a Computational Fluid Dynamics (CFD) simulation on the ammonia solar and synthesis reactors has been performed. The CFD commercial package FLUENT is used for the simulation study and all the important mechanisms for packed bed reactors are taken into account, such as momentum, heat and mass transfer, and chemical reactions. The FLUENT simulation reveals the profiles inside both reactors and compared them with the profiles from the MATLAB model. The good agreement between both models gives hope for the feasibility of the design.