Development of a simulation-software for a hydrogen production process on a solar tower. (February 2015)

• Record Type: Journal Article
• Authors: Säck, J.-P.; Roeb, M.; Sattler, C.; Pitz-Paal, R.; Heinzel, A.
• Is Part Of: Solar energy. Volume 112(2015)
• Page Start: 205
• Page End: 217
• Publication Date: 2015-02
• Subjects: Solar tower system -- Temperature control -- Two step thermochemical cycle -- Heliostat field control -- Solar hydrogen; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2014.11.026
• Languages: English
• ISSNs: 0038-092X

Abstract

Highlights: Development of a simulation software for a hydrogen production process with a solar tower system. Dynamical simulation and control of the heliostat field, the reactor and the process in one simulation. On/offline simulation for the operational behavior and for the post- and pre-analysis. Controllability of the temperature of the two step thermo chemical cycle with iron oxides on a solar tower system. Possibility for a future integration of the model into commercial chemical solar tower plants for control. Abstract: A simulation and control model for a two-step thermo-chemical water splitting cycle using metal oxids for the generation of hydrogen with a solar tower system as heat source has been developed. The simulation and control model consists of three main parts, the simulation of the solar flux distribution on the receiver, of the temperatures in the driven reactor modules and the produced hydrogen in the metal oxide. The results of the three parts of the simulation model have been evaluated by comparing and validating them with experimental data from the Hydrosol 100 kWth pilot plant at the Plataforma Solar de Almería (PSA) in Spain. With the overall model of the hydrogen production plant that was created, an evaluation of the two-step thermochemical cycle process in combination with a solar tower system was performed. The model was used to perform parametric studies for the development of the plant and the operation strategies. For this purpose, a provision in the overall model was integrated. The simulation helps to reduce the frequency of using the flux measurement system and can be used for the heliostat field control, in particular for the temperature control in the solar chemical reactor modules. Because of these promising results the overall system model is being extended to enable a use as a control model with controller for the temperature control of the two core reactions in the process. The central control variable of the process control was the operating temperatures for the hydrogen production and the regeneration of the two modules. The process control with its PI controller turned out suitable to compensate diurnal changes of solar input power as well as certain statistical fluctuation due to cloud passage. At the same time the limits of the operability and controllability of the process became clear in terms of the minimum of solar power needed and maximum acceptable gradients. With this experience an operating strategy, the basic parameters of the system in operation, especially the starting up and shutdown procedures, regular operation and the response to disturbances were selected and optimized. With this operation/control strategy such a complex system can be operated in the future on a commercial scale automatically. The obtained results can also be adapted for other solar chemical processes.