Solid oxide fuel cell (SOFC)/ gas turbine (GT) hybrid systems possess the capability to nearly double the efficiency of standard coal-fired power plants which are currently being used for large scale power production. For the purposes of investigating and developing this technology, a SOFC/GT hybrid test facility was developed at the U.S. DOE National Energy Technology Laboratory (NETL) in Morgantown, WV as part of the Hybrid Performance (HyPer) project. The HyPer facility utilizes hardware-in-the-loop technology to simulate coupled SOFC operation with gas turbine hardware in a hybrid arrangement. This paper describes and demonstrates the capabilities of the one-dimensional, real-time operating SOFC model that has been developed and successfully integrated into the HyPer facility. The model presented is designed to characterize SOFC operation over a broad and extensive operating range including inert heating and cooling, standard “on-design” conditions and extreme off-design conditions. The model receives dynamic, system-dependent modeling inputs from facility hardware and calculates a comprehensive set of SOFC operational responses, thus simulating SOFC operation while coupled with a gas turbine. In addition to characterizing SOFC operation, the model also drives the only heat source in the facility to represent fuel cell subsystem release of thermal effluent to the turbine subsystem. Operating parameters such as solid and oxidant stream temperatures, fuel stream compositions, current density, Nernst potential and polarization losses are produced by the model in spatiotemporal manner. The capability of the model to characterize SOFC operation, within dynamic hybrid system feedback, through inert heat up and a step change in load is presented and analyzed.
The system response to an initial electric load of the fuel cell during the startup of a direct-fired fuel cell turbine power system was studied using the Hybrid Performance (Hyper) project hardware-based simulation facility at the U.S. Department of Energy, National Energy Technology Laboratory for a range of input fuel compositions. The facility was brought to a steady condition at a temperature deemed adequate to minimize stress on the fuel cell during the initial load transient. A 1D distributed fuel cell model operating in real-time was used to produce individual cell transient temperature profiles during the course of the load change. The process was conducted with humidified hydrogen, and then repeated with various syngas compositions representative of different gasifier technologies. The results provide insight into control strategy requirements for mitigation of expected fuel cell failure modes relevant to available gasifier technology.
A one-dimensional, distributed solid oxide fuel cell (SOFC) model, capable of operating in real time, has been developed for integration into a direct-fired SOFC/gas turbine pilot scale hybrid facility using hardware-in-the-loop simulation (HiLS). Preliminary studies of the impact of the initial start-up of the hybrid system on transient thermal response in the SOFCs have been conducted. Further investigation of the impact of process parameters upon the fuel cells is also presented in this paper. Specifically, the influence of cathode airflow rate and inlet temperature upon thermal response during inert preheating is studied and analyzed in both the spatial and temporal regimes. Particular emphasis is placed upon the evolution of spatial and temporal temperature derivatives (possibly leading to undesirable thermally induced stresses) in the ceramic SOFC material.
Solid-oxide fuel-cell (SOFC)/gas-turbine hybrid systems possess the capacity for unprecedented performances, such as electric efficiencies nearly twice that of conventional heat engines at variable scale power ratings inclusive of distributed generation; however, reliably integrating such technologies is critical. Dynamic operability challenges ranging from surge-stall events in the turbomachinery to threatening thermally induced stresses within the fuel cells are formidable. An effective means of characterizing the operability of such systems requires a simulation approach of high fidelity yet reduced sacrificial risk associated with empirical investigation of SOFC stacks. Accordingly, a unique cyber-physical simulation (CPS) was developed inclusive of a spatio-temporal SOFC computational model interfaced with a retrofitted turbine. The model had an extensively broad operating range, as compared to other models that have been developed, with the capability to characterize inert heating, electrochemical start-up, and on and off design operation. A comprehensive parametric characterization was done for initial electrochemical light-off with variability in compressor by-pass valve position and initial fuel-cell load for both closed loop and open loop (OL) turbine speed system configurations. The impact of cold-air (CA) by-pass, as well as initial fuel-cell load on system parameters that directly affect SOFC operation, such as inlet air temperature, pressure, and flow, along with turbine speed and thermal effluent dynamics are presented and discussed. Additionally, the full spatio-temporal capability was exhibited and utilized in examining the impact of electrochemical start-up upon SOFC temperature and temperature gradients as a result of local current density and by-product heat distribution. Ultimately, a comprehensive parametric study, characterizing SOFC and hybrid system response to electrochemical start-up along the decision variable values of initial fuel-cell load, as well as CA by-pass valve position, was completed; this illustrated an advanced simulation platform for gathering such insights about developmental fuel-cell systems.
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