Fuel cell hybrid systems, dynamics and surge analysis

The improvement of energy system performance has led to the development of efficient dynamic compressors able to achieve high compression ratios, high flow rates of fluid and reduced weights. As it normally happens by nature, the higher is the desired performance the more difficult is to achieve it; in the case of dynamic compression, the need to reach increasingly higher compression ratios and larger operational flexibility involves the occurrence of unsteady phenomena such as rotating stall and surge. These two problematic phenomena characterize compressors with violent decrease of performance and severe damage to machines, consequently the topic has been object of several studies over the years. The intensity and behavior of surge are tightly connected to the amount of volumes coupled to the turbo machinery during its operation. For this reason, surge phenomenon is strongly felt in fuel cell gas turbine hybrid system applications, where, primarily the fuel cell, then all the other components (e.g. heat exchangers if present), auxiliaries and connections constitute the vast majority of the volume contained in the system. This work is organized into three macro-chapters, each one is focused on a specific application. The descriptive organization follows the chronological order in which the case studies were addressed and follows the level of maturity of the research object of this program. Therefore, in the following chapters each single case study is presented and discussed separately. The following list anticipates what are the main outcomes and learnings which will be encountered through the text. In this way the candidate wants to clearly summarize what can be considered as primary steps, contribution to the energy systems modeling research field and main outputs of this work: - Mathematical descriptions for components development with integrations and improvements will be described application by application. - Description of the proposed steps followed by the methodologies used to extend compressor maps for surge simulation purposes. A mix of analytical and empirical methods will be suggested through this work. - A method for dynamic delays characterization of complex piping systems named τ-Flow approach have been proposed and applied to these studies. - Parametric studies to investigate the effect of different parameters such as volume size, shaft inertia and equivalent lengths, on the surge cycles characteristics. Impacts of these characteristics will be analyzed in different control configurations where options are applicable. - Simulation results, experimental comparison and validation will be presented at the end of each macro-chapter as completion of the analysis. - The possibility to recover from a surge event acting on by pass valves will be also simulated and presented in the context of Hyper facility analysis.