Calculating the System Efficiency of the NETL Gas-Turbine/Fuel-Cell Hybrid System Using a Fully Coupled Lumped Parameter System Model

Abstract

Thermodynamic efficiency must be considered in the effective analysis of gas turbine fuel cell power generation system performance. In most numerical simulations of hybrid systems, the use of compressor maps and turbine maps are neglected. It is assumed that the design criterion generated by the system model can be met by the manufacturer of these items. These system models may use partial information from a compressor map, or a turbine map, but they fail to match all the operating conditions of both maps in a hybrid configuration. Also, to simplify the calculations that are performed by the complex hybrid system models, the effects of heat transfer and fluid dynamic drag are often decoupled. When system calculations are done in this way, the resulting calculations for system efficiency may suffer error. Hybrid system designers need a simple method to calculate the system performance directly from the maps of real compressors and real turbines that currently exist, and that would be part of a hybrid system. In this work, a simple procedure is illustrated where a coupled analysis of the various system components is performed and included as part of the system model. This analysis is done using the compressor and turbine maps of the hybrid performance project hardware at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). Model parameters are tuned using experimental conditions and results are obtained. The results show the importance of aerodynamic coupling in system models, and how this coupling affects the system efficiency calculations. This coupling becomes important especially for the variable density flows that are typically found in combustors, heat exchangers and fuel cells.