No abstract

Fuel cell hybrid power systems have potential for the highest electrical power generation efficiency. Fuel cell gas turbine hybrid systems are currently under development as the first step in commercializing this technology. The dynamic interdependencies resulting from the integration of these two power generation technologies is not well understood. Unexpected complications can arise in the operation of an integrated system, especially during startup and transient events. Fuel cell gas turbine systems designed to operate under steady state conditions have limitations in studying the dynamics of a transient event without risk to the more fragile components of the system. A 250kW experimental fuel cell gas turbine system test facility has been designed at the National Energy Technology Laboratory (NETL), U.S. Department of Energy to examine the effects of transient events on the dynamics of these systems. The test facility will be used to evaluate control strategies for improving system response to transient events and load following. A fuel cell simulator, consisting of a natural gas burner controlled by a real time fuel cell model, will be integrated into the system in place of a real solid oxide fuel cell. The use of a fuel cell simulator in the initial phases allows for the exploration of transient events without risk of destroying an actual fuel cell. Fuel cell models and hybrid system models developed at NETL have played an important role in guiding the design of facility equipment and experimental research planning. Results of certain case studies using these models are discussed. Test scenarios were analyzed for potential thermal and mechanical impact on fuel cell, heat exchanger and gas turbine components. Temperature and pressure drop calculations were performed to determine the maximum impact on system components and design. Required turbine modifications were designed and tested for functionality. The resulting facility design will allow for examination of startup, shut down, loss of load to the fuel cell during steady state operations, loss of load to the turbine during steady state operations and load following.

Managing the temperatures and heat transfer in the fuel cell of a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid fired on coal syngas presents certain challenges over a natural gas based system, in that the latter can take advantage of internal reforming to offset heat generated in the fuel cell. Three coal based SOFC/GT configuration designs for thermal management in the main power block are evaluated using steady state numerical simulations developed in ASPEN PLUS. A comparison is made on the basis of efficiency, operability issues and component integration. To focus on the effects of different power block configurations, the analysis assumes a consistent syngas composition in each case, and does not explicitly include gasification or syngas cleanup. A fuel cell module rated at 240 MW was used as a common basis for three different methods. Advantages and difficulties for each configuration are identified in the simulations.

In recent years there has been significant interest in using the heat generated from the normal operation of a solid oxide fuel cell (SOFC) to supplant the normal combustion process of a gas turbine system. By doing this a gas turbine fuel cell hybrid power generation system is formed. Because the heat produced by a SOFC is utilized by the turbine to produce work, the hybrid system can have an overall system efficiency that greatly exceeds those of either the stand alone SOFC system, or the stand alone gas turbine system. One of the most critical problems that must be addressed in gas turbine fuel cell hybrid technology is temperature control. A hybrid system that is designed to operate efficiently for a given base load may not be easily extended to accommodate peek load. In this paper a simple hybrid system configuration using a standard SOFC and a single compressor-turbine pair is presented. This simple system is used to establish the effect that key configuration parameters have on system temperatures. The configuration model is then scaled over a range of fuel input and power output to show the limitations of the system. The system is modeled using the ASPEN PLUS® simulation software with special modules to calculate fuel cell performance.