Dynamic Simulation of a Pressurized 220kW Solid Oxide Fuel-Cell–Gas-Turbine Hybrid System: Modeled Performance Compared to Measured Results

R. A. Roberts J. Brouwer e-mail: jb@nfcrc.uci.edu National Fuel Cell Research Center, University California, Irvine, Irvine, CA 92697-3550 Dynamic Simulation of a Pressurized 220 kW Solid Oxide Fuel-Cell–Gas-Turbine Hybrid System: Modeled Performance Compared to Measured Results Hybrid fuel-cell–gas-turbine (FC/GT) systems are technologically advanced systems that are promising for electric power generation with ultralow emissions and high efficiency for a large range of power plant sizes. A good understanding of the steady-state and dynamic performance of a FC/GT system is needed in order to develop and advance this hybrid technology. In this work, a detailed dynamic model of a solid oxide fuel cell/gas turbine (SOFC/GT) system has been developed. The system that is simulated represents the 220 kW SOFC/GT hybrid system developed by Siemens Westinghouse. Results of the dynamic model and experimental data gathered during the operation and testing of the 220 kW SOFC/GT at the National Fuel Cell Research Center are compared and presented. 关DOI: 10.1115/1.2133802兴 Introduction and Background Fuel cell/gas turbine 共FC/GT兲 hybrids integrate high- temperature fuel cells with gas turbine engines in a manner that converts fuel cell thermal energy through turbo machinery to power compressors and/or electric generators. In both thermody- namic simulation and experiment, these hybrid systems have dem- onstrated lower environmental impact compared to conventional combustion-driven power plants. Lower carbon dioxide emissions can be achieved through higher fuel-to-electrical efficiencies, while NO x and other criteria pollutant emissions are greatly re- duced by primary electrochemical conversion of the fuel versus the combustion process of conventional plants 关1兴. In this work, a dynamic model of a hybrid system is developed and applied to analyze a specific hybrid cycle that is applicable to distributed generation. More complex cycles have been considered for larger scale power plants that may utilize a combined cycle to drive the efficiency up and the environmental impact down 关2兴. Today much work is being done to reduce the cost and increase the reliability of solid oxide fuel cell 共SOFC兲 systems. Several cell geometries are being advanced by fuel cell manufacturers includ- ing tubular and planer SOFC designs, and even cell geometries that combine planer and tubular features. Each geometry has its advantages and disadvantages with regard to thermal expansion compliance, power density, potential cost, manufacturability, and internal resistivity 关3兴. Many companies are advancing these dif- ferent types of SOFCs, but no commercial products exist today. Only demonstration and prototype systems have been built and tested to date. Mathematical models provide a cost-effective and efficient tool in aiding the development of SOFCs and SOFC/GT systems. Sev- eral entities around the world have developed steady-state simu- lation capabilities for FC/GT systems. These research groups in- clude efforts at the Georgia Institute of Technology, University of Genova, NFCRC, Nanyang Technical University, and others Manuscript received February 8, 2005; final manuscript received August 19, 2005. Review conducted by Subhash C. Singhal. 18 / Vol. 3, FEBRUARY 2006 关2–8兴. Dynamic FC/GT simulation capabilities are less common, but increasingly being developed as the demand for dynamic un- derstanding and controls development grows. Examples of previ- ous dynamic simulation efforts include work at the National En- ergy Technology Laboratory and FuelCell Energy among others 关9–13兴. Model validation is very important, and there remains a great need to produce experimental hybrid system data. To date there have been two hybrid systems built and success- fully demonstrated. The first uses an atmospheric fuel cell located after the turbine exhaust has been built and demonstrated by Fu- elCell Energy that integrated a molten carbonate fuel cell and a Capstone C30 gas turbine. This system successfully ran for 2900 h in grid-connected mode at 51.7% fuel-to-electrical effi- ciency. See Ghezel-Ayagh et al. 关14兴 for more information on this system. The second system uses a pressurized fuel cell located between the compressor and turbine, which is the system of direct interest to the current work. Experiment Description Siemens Westinghouse developed the very first pressurized SOFC/GT hybrid system using their tubular SOFC stack design. This system, presented in Fig. 1, was tested at the NFCRC with support from Southern California Edison, the U.S. Department of Energy, and others. The system was designed, constructed, and tested to demonstrate and prove the hybrid concept. The system operated for over 2900 h and produced up to 220 kW at fuel-to- electricity conversion efficiencies of up to 53%. In parallel, NFCRC developed dynamic simulation capabilities for each of the system components together with a simulation framework for modeling and developing control strategies for integrated SOFC/GT systems. A diagram of the integrated SOFC/GT system is presented in Fig. 2. This system is comprised of a tubular SOFC with inte- grated internal reformer and anode off-gas oxidizer as illustrated in Fig. 3. These components 共stack, reformer兲 are placed between the compressor and turbine so that they operate under pressurized conditions. The gas turbine is a dual shaft Ingersoll-Rand 75 kW Copyright © 2006 by ASME Transactions of the ASME Downloaded From: http://fuelcellscience.asmedigitalcollection.asme.org/ on 12/02/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use