This paper describes the experimental validation of two different transient models of the hybrid fuel cell/gas turbine facility of the U.S. DOE-NETL at Morgantown. The first part of this work is devoted to the description of the facility, designed to experimentally investigate these plants with real components, except the fuel cell. The behavior of the SOFC is obtained with apt volumes (for the stack and the off-gas burner) and using a combustor to generate similar thermal effects. The second part of this paper shows the facility real-time transient model developed at the U.S. DOE-NETL and the detailed transient modeling activity using the TRANSEO program developed at TPG. The results obtained with both models are successfully compared with the experimental data of two different load step decreases. The more detailed model agrees more closely with the experimental data, which, of course, is more time consuming than the real-time model (the detailed model operates with a calculation over calculated time ratio around 6). Finally, the TPG model has been used to discuss the importance of performance map precision for both compressor and turbine. This is an important analysis to better understand the steady-state difference between the two models.

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test, and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide a means of quantifying risk mitigation strategies. An open-loop system analysis regarding the dynamic effect of bleed air, cold air bypass, and load bank is presented in order to evaluate the combination of these three main actuators during emergency shutdown. In the previous Hybrid control system architecture, catastrophic compressor failures were observed when the fuel and load bank were cut off during emergency shutdown strategy. Improvements were achieved using a nonlinear fuel valve ramp down when the load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shutdown activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.

The adoption of solid oxide fuel cell (SOFC) technology in power generation has been limited, in no small part, by material degradation issues affecting the stack lifetime, and hence, the economic viability. A numeric study was conducted to determine if the life of an SOFC could be extended when integrated with a recuperated gas turbine system. Dynamic modeling tools developed at the National Energy Technology Laboratory (NETL) for real-time applications were applied to evaluate life to failure for both a standalone SOFC and a hybrid SOFC gas turbine. These models were modified using empirical relations to experimental degradation data to incorporate degradation as a function of current density and fuel utilization. For the control strategy of shifting power to the turbine as fuel cell voltage degrades, the SOFC life could be extended dramatically, significantly impacting the economic potential of the technology.

In pursuing the implementation of highly efficient, emission-free power, the U.S. Department of Energy (DOE) is looking to the development of hybrid power systems that make use of the coupling of an electrochemical device with a heat engine, or more specifically, a solid oxide fuel cell (SOFC) and a gas turbine.

The U.S. Department of Energy (DOE)-National Energy Technology Laboratory (NETL) in Morgantown, WV has developed the hybrid performance (HyPer) project in which a solid oxide fuel cell (SOFC) one-dimensional (1D), real-time operating model is coupled to a gas turbine hardware system by utilizing hardware-in-the-loop simulation. To assess the long-term stability of the SOFC part of the system, electrochemical degradation due to operating conditions such as current density and fuel utilization have been incorporated into the SOFC model and successfully recreated in real time. The mathematical expression for degradation rate was obtained through the analysis of empirical voltage versus time plots for different current densities and fuel utilizations.

Current design concepts for hybrid systems call for the use of presently available turbine systems. Simply stated, the combustor of a turbine system is replaced with a high temperature fuel cell whose excess heat is used to drive the turbine. However, the startup of a turbine in such a direct fired fuel cell turbine hybrid system is made problematic through the increased pressure losses introduced by heat recuperation, and the relatively large cathode volume now present between the compressor discharge and the turbine inlet. This work evaluates the use of compressor bleed air to avoid stall and surge during the startup of a fuel cell turbine hybrid power system using the Hybrid Performance (Hyper) project hardware simulation facility at the National Energy Technology Laboratory (NETL), U.S. Department of Energy. Because integration of a fuel cell and often multiple recuperators into the compressed air stream results in a higher required pressure ratio for any given compressor inlet mass flow, a strategy must be developed to avoid compressor stall during startup. Turbine starts were attempted using the NETL Hyper project facility over a range of compressor bleed mass flows. The experimental facility at NETL makes use of a natural gas burner controlled by a real time fuel cell model to simulate the thermal output of a solid oxide fuel cell. Pressure vessels, used for simulating the cathode and post combustion volumes, and exhaust gas recuperators are integrated into the system with a modified turbine and compressor on a single shaft. The startup profiles are compared to the stall line of the compressor map to quantitatively evaluate the efficacy of the applied method in avoiding stall and surge during startup events.