Dynamische Modellierung von solarthermischen Kraftwerken mit Salzreceivern

Abstract

The aim of this thesis is the investigation of the dynamic behavior and operation of a solar power tower (SPT) plant with a cylindrical receiver using molten salt as heat transfer fluid. The investigation is focused on the solar components of the plant, the heliostat field and the receiver. The dynamic behavior during cloud transients is the center of discussion. For this purpose, a dynamic model of a SPT plant is developed by coupling existing models of heliostat field and receiver. The presented thesis first provides background information about the SPT technology with reference to molten salt SPT and introduces the utilized models. As a next step the state of the art in modelling SPT plants as well as cloud transients is investigated and strategies for the operation of a SPT pant are presented. The thesis then explains the methods that are applied to create a model of SPT plant for co-simulation and to model cloud transients. A graphical user interface is developed to define operational modes, aiming strategies and to create cloud fields. Three models are available for the investigation of cloud transients, that allow the creation of various cloud fields. After the model is introduced a validation of the developed models is conducted. The results and discussions simulations are presented in the fifth chapter before the final conclusions are drawn. The major part of this investigation is related to cloud transients, but also transients between aim point configurations are considered. An operational mode for the process of filling and draining the receiver was also developed but these processes could not be simulated because the required two-phase model of the receiver was not available yet. The investigation of cloud transients suggest that a cloud standby feature is required for a save operation of the receiver. Simulations without this feature could not be finished as temperatures exceeded 900 °C which is far beyond the allowable temperature limit of 600 °C. During the process of covering the heliostat field an increase in maximum salt temperature can be observed on the opposite side of the receiver to the direction from which a cloud is approaching. This increase was found to be most critical for a cloud approaching from the south of the field as temperatures on the northern receiver panels increase. For clouds travelling with higher velocity the gradient as well as the maximum temperature also increased. The transients between aim point configurations are conducted within half a second but an increase in flux density of up to 20 % can be observed during the process of changing the aim points. At last suggestions for an improved plant operation are made based on the results and observations made in this thesis.