Mechanical equilibrium operation integrated modelling of recuperative solid oxide fuel cell - gas turbine hybrid systems: Design conditions and off-design analysis

A novel model integrating mechanical equilibrium operation, electrochemical reactions and other thermodynamic processes has been built in this research to gain energetic and operational insights into recuperative solid oxide fuel cell - gas turbine hybrid systems. Determination mechanism for equilibrium running is proposed for both design stage analysis and off-design operation through reanalysis of classical speed and flow compatibility requirements. The coupling with solid oxide fuel cells and inclusion of a recuperator substantively introduces several independent variables to the related equation, while the number of independent parameters decreases in modelling when matching issues of turbomachinery are taken into account. Compared to simple hybridization, there are increasingly complex mutual influence and constraints between upstream and downstream parameters that are linked by the heat recovery process. Quantitative analysis of factors in turbine design shows 14-16% higher system efficiency with component pressure losses taken into consideration. When the turbine is appropriately designed, an electric efficiency of 68% can be achieved with recuperator effectiveness of 0.9. Results also highlight the significantly expanded operating ranges of turbomachinery under lower recuperator effectiveness of 0.8 as compensation for a 3% lower electrical efficiency at design conditions. A performance map for the proposed system is developed based on off-design operation analysis with stable running state ensured throughout.