Simulation of the Dynamic Behavior of a Solar Power Tower Using a Molten Salt Receiver and Evaluation of Control Strategies

Kurzfassung

Solar power plants regularly face transient operation conditions e.g. due to clouds. These dynamic conditions result in thermal stresses to the mechanical system due to tempera-ture gradients and they may also lead to an exceedance of temperature limits. The over-all target is to keep the outlet temperature constant while maintaining all operation limits by utilizing an enhanced control strategy and so to ensure a high durability of the entire system. The objective of this work is to simulate and analyze the behavior of the combined sys-tem of the molten salt receiver and the heliostat field of a solar tower power plant during cloud transients and to elaborate improved control strategies. In a first step, an existing model is customized to a specific receiver type and integrated into an existing simulation environment which had to be adapted. Second, those situations which appear to be most demanding to the system were defined and simulated. The analysis of the results allows to rate the performance of the system and to identify its challenges. They can be reduced to three basic principal effects which will be discussed in detail. On this basis, alternative control strategies with the potential to improve the operation are elaborated, analyzed and evaluated by simulation. They include an enhanced feed-forward control which accounts for the changing temperature profile during transients and an uneven flux distribution and which prevents fluid temperature limit exceedances and detects and reacts to sequential flux increases. Furthermore, they include a mech-anism which impedes local excess film temperatures by raising the mass flow rate when necessary. Moreover, temperature gradients are addressed. What is more, a mechanism that intends to prevent a sudden unexpected rise of the flux is analyzed and compared to a state-of-the-art system which increases the mass flow rate (Cloud Standby).