There is an increasing need for adequate modelling and simulation tools for the design and analysis of fuel cell systems. In the present contribution, a modular modelling strategy is proposed, which is based on network theory for chemical engineering processes.According to this network theory, a fuel cell system is decomposed into elementary units on several hierarchical levels (process unit level, phase level, storage level). After decomposition, the model formulation starts on the storage level: electrochemical source terms were combined with the diffusive and convective transport phenomena and state equations, forming an elementary unit of the phase level. On the phase level several thermodynamic phases (e.g. fluid compartments, electrode backings, catalyst layers, and the membrane electrolyte) are aggregated to a single fuel cell unit. Finally on the top level, the process unit level, single cells or fuel cell stacks are combined with other process units to form a complete process model.This modelling procedure is demonstrated with a simple proton exchange membrane fuel cell system operated with hydrogen and oxygen.

Communications three-phase equilibrium and the extract will never contain more acetone than the carbon-dioxide-rich phase of the three phase equilibrium. This behavior could be observed during the experiments.Thus, an important conclusion can be drawn from the experiments: if in an extraction process multiphase equilibria have to be taken into account, it is crucial which phase is chosen as the continuous one. In the present case, this is the heaviest, water-rich phase. Modeling and SimulationTo simulate the behavior of this supercritical extraction process with multiphase equilibrium, an equilibrium-stage model based on the phase-equilibrium calculations presented above was used. To achieve quantitative agreement between experiment and simulation, a stage efficiency according Murphree was introduced. The definition of this efficiency was extended in this work to a three-phase equilibrium stage.This work is presented in detail in [10]. AcknowledgementThe authors gratefully acknowledge the support provided by Privatdozent Dr. W. Leitner and Max-Planck-Gesellschaft for the experimental studies on the high-pressure extraction process as well as the financial support provided by Deutsche Forschungsgesellschaft DFG and SFB 412 ªComputer Aided Modeling and Simulation for Analysis, Synthesis and Operation in Process Engineeringº. IGCC (integrated gasification combined cycle) plants offer the opportunity to utilize fossil energy sources, like coal or heavy refinery residues, to satisfy increasing energy demand while considering strict environmental constraints [1]. Such a plant consists of a combined power cycle, a fuel gasifier with downstream fuel gas conditioning and an air separation unit (ASU), where the oxygen required for gasification is produced. By using this concept efficiencies of up to 50 % can be achieved. Compared to conventional coal-fired plants the use of an IGCC plant provides a considerable potential for CO 2 reduction.First operational experiences with demonstration plants built in USA and Europe indicate the existence of significant potential for development to achieve a level of automation that is common in plant design. This challenge results in the novel linkage of different plants, such as gasifier, air separation unit and gas turbine. Large amounts of different feedback complicate the prediction of operational behavior and plant trips and require the application of a dynamic plant simulation. 1126 CommunicationsA matter of particular interest is the coupled air-side integration between gas turbine and air separation unit ( Fig. 1). By linking these two components undesired fluctuations of mass flow can occur within the system during changing load demands. These fluctuations are due to the different responses of each of the coupled system components. Therefore, for failure-free joint operation of air separation unit and gas turbine including a further air compressor new control concepts are required, which can be designed and tested with the help of a dynamic simulation model.The cryogenic recti...

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