Dynamic model of 5 kW SOFC CHP power plant

A dynamical model for a 5 kW solid oxide fuel cell (SOFC) combined heat and power (CHP) plant system has been composed. The model is based on a real test rig being constructed and used at VTT Technical Research Centre of Finland. The purpose of the test rig is to examine how the stack and other components interact in order to gain information on efficient plant design and to study optimal system control strategies. To support these tasks and to obtain further information that cannot be retrieved by operating the test system alone, model development has been undertaken. The model contains the following main components of the real system: the autothermal reforming unit, SOFC stack, catalytic afterburner, anode and cathode heat exchangers, and water recuperator. The model can be applied both to steady-state and to transient operation conditions. By using the model, development of the control system and optimization of the operation parameters such as component temperatures, flow rates, the fuel/air ratio and the steam/fuel ratio of the stack and the autothermal reformer unit can be carried out time and cost efficiently. Furthermore, the investigation of different operational aberrations or states of emergency, e.g. overload situations or emergency shutdowns, is made feasible by the model. The model has been constructed using Advanced Process Simulation Environment (APROS) software that has been developed for ca. 20 years at VTT. APROS provides solution algorithms and model libraries for the dynamic modelling of flow processes. It is in active use for example in the combustion power, nuclear power and pulp and paper industry. The model libraries of APROS have been validated against real process experiments. Currently, the APROS software is being implemented for fuel cell power plant modelling by the preparation of models for reforming units, catalytic afterburners, sulphur removal units and SOFC stacks. The 5 kW stack, delivered by Research Centre Jülich (FZJ), will be mounted to the test rig in October this year. After this, the applicability of the model will be verified by comparisons to measurement data obtained from test runs using the test rig. The verification will be performed against data from runs both in steady-state and in transient conditions. This work is a part of the national FINSOFC project coordinated by VTT. The aim of this project is to promote the know-how and commercial activity in the field of SOFCs in Finland.