Balance of Plant Modelling in the Hybrid Power Plant Project

Kurzfassung

Hybrid power plants offer a promising way of producing electricity at high efficiencies. The DLR Institute of Technical Thermodynamics is part of a research partnership developing a hybrid power plant. Since the control strategy of a hybrid power plant is complex and demanding the development process is optimised by modelling components and the overall plant. The control system is developed on the basis of the power plant model. Therefore the models have to be highly reliable and fast concerning computing time. The presentation focuses on the modelling of the fuel cell system in the Hybrid Power plant project. A model library for MATLAB Simulink containing several fuel cell models as well as balance of plant components has been developed. Central part of the fuel cell system is the stack itself. A detailed model of a tubular solid oxide fuel cell was programmed including detailed electrochemistry as well as heat and mass balances. The model is validated on a Siemens SFC-5 system. The detailled model is to complex for the integration into a real-time system simulation. Hence a system stack model was derived from the detailed model. To completely model a SOFC generator the most important parts are the balance of plant (BoP) components. Those feature ejectors for anode recirculation, reformer and desulphurisation. The ejector is modelled as a 1D appartus with a 2D velocity distribution in the premixing section. Its main purpose is to mix recirculated anode gas with fresh natural gas thus delivering steam for the reforming reaction. The reformer is modelled as a 1D fixed bed steam reformer utilising steam reforming and water gas shift reactions. The reactions are always at equilibrium conditions. The reformer is discretised along the flow direction delivering additional information on the reactions inside the vessel. The model incorporates heat conduction between elements as well as convection of gas through the reformer. A link is integrated to exchange heat between the fuel cell and the reformer based on radiation heat transfer thus cooling the stack and supplying heat to the reformer. The presentation will focus on the modelling of the BoP components and show major influences on the performance of the BoP components as well as results from simulations of the system.