Solid Oxide Fuel Cell/Gas Turbine Hybrid Power Plant - Model Based Design of Control Strategies

The continuously increasing demand for electrical energy requires the development of power plants with high efficiencies and low emissions. A hybrid power plant consisting of a solid oxide fuel cell (SOFC) system coupled with a gas turbine (GT) promises to fulfill these requirements and also has the advantage of offering a wide range of applications from several 10 kW to multi MW. Indirectly and directly coupled systems are possible, mainly distinguished by the higher operating pressure and reduced heat transfer losses of the directly coupled SOFC system. Since the directly coupled systems with elevated SOFC operating pressure promise to outperform the system efficiency of the indirectly coupled systems [1-2], the DLR has been investigating the corresponding fundamentals and requirements of a directly combined fuel cell and gas turbine power plant for several years. An elementary kinetic SOFC stack model was developed and experimentally validated [3] in a wide range of operating conditions. This model was integrated into an existing model of a gas turbine [4]. The model is used to carry out stationary hybrid power plant simulations in order to investigate how variations in operating strategy and component characteristics influence the performance of the hybrid power plant as well as the operating conditions of the SOFC. Results show that varying electrical SOFC power while keeping electrical gas turbine power constant strongly influences the overall electrical efficiency of the hybrid power plant. The experimental and simulation results are to be used to adapt the existing models from stationary to transient regime. This allows for future development of operation and control strategies. A pilot power plant is to be designed and commissioned to validate the transient model accordingly. [1] Henke, M., Willich, C., Westner, C., Leucht, F., Leibinger, R., Kallo, J., & Friedrich, K. A. (2012). Effect of pressure variation on power density and efficiency of solid oxide fuel cells. Electrochimica Acta, 66, 158–163. [2] Zhang, X., Chan, S. H., Li, G., Ho, H. K., Li, J., & Feng, Z. (2010). A review of integration strategies for solid oxide fuel cells. Journal of Power Sources, 195(3), 685–702. [3] M. Henke et al., Modeling and Experimental Study of Pressurized Solid Oxide Fuel Cells, ModVal 9, Campus Sursee, Switzerland 2012 [4] T. Panne et al., Themodynamic Process Analyses of SOFC/GT Hybrid Cycles, 5th IECEC, St. Louis, Missouri, USA, 200

Pressurized SOFC systems for stationary applications

Solid oxide fuel cell (SOFC) systems show very high electrical efficiencies even at small sizes. DLR applies a multidisciplinary and multiscale approach to designing and optimizing pressurized SOFC systems for hybrid power plants. A large Simulink model library was developed featuring balance-of-plant components as well as fuel cell models. Recently a pressurized cell test rig was taken into operation

Pressurized Solid Oxide Fuel Cells: Operational Behavior

The operational behavior of SOFC short stacks at elevated pressures up to 7 bar was examined. The experiments were performed on planar, anode-supported 5-cell short stacks. First, the pressure-dependency of performance at steady state at different relevant operating conditions is shown, and then temperature variations and gas composition change as well as their effects on pressurized SOFC are presented

Solid Oxide Fuel Cell – Gas Turbine Hybrid Power Plant

A model of a hybrid power plant consisting of SOFC and a gas turbine is presented. Simulations are carried out for a different number of SOFC stacks while keeping the output power of the SOFC constant. Results show that the effect of stack number on system performance is only marginal within the investigated range. Operating conditions of the SOFC, however, are strongly influenced

Experimental Investigation of�Anode/Cathode Differential Pressures �for a SOFC/Gas Turbine Hybrid Power Plant

Providing electrical energy with a reduced CO2 footprint and in a sustainable way is a significant challenge for the future. Therefore the research community is intensively studying more effective ways to provide electricity to consumers. In this respect a hybrid power plant, a combination of SOFC and gas turbine, is highly attractive and a research prototype is being developed at the German Aerospace Center. The hybrid power plant consists of a pressurized solid oxide fuel cell (SOFC) and a small gas turbine. It has the possibility to provide electrical energy with high electrical efficiencies. In the hybrid power plant the SOFC will be operated at elevated pressure which enhances the electrical power output of the SOFC. The increased SOFC cathode pressure is maintained by the gas turbine compressor. Pressure differences between the two electrode volumes lead to mechanical stresses and may lead to failure of the SOFC. The durability of the SOFC stack related to pressure differences between anode and cathode compartment was investigated with a planar two layer SOFC stack at operating temperature of 850 °C. The tests were carried out with stationary pressure changes to determine operational limits and potential reasons for failure. The testing procedure and the results will be explained and discussed