UC Irvine

This research presents a system design and analysis, and transient \textit{control} and optimization of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems. The main features of SOFC-GT power systems include high efficiency, virtually zero emission of criteria pollutants, and low acoustic signature compared to conventional power production technologies. Focus of this dissertation is the investigation of control strategies and transient performance characteristics of hybrid SOFC-GT systems, using computational fluid dynamics methods.

A novel control system is developed for a SOFC-GT system to follow dynamic power demands associated with locomotives while keeping all of the components and system operating variables within acceptable limits of performance. The voltage variation is also greater at lower fuel utilization. The stack temperature difference is highly dynamic at low fuel utilization. In addition, detailed analyses of potential SOFC-GT locomotive production and operation costs in comparison to other low pollutant emitting alternatives is accomplished. SOFC-GT locomotives are projected to produce lower operating costs compared to the catenary-electric alternative, and significantly lower operating costs compared to the battery-electric alternative.

A part of this research is devoted to a better understanding of turbulent unsteady flows in gas turbine systems that is necessary to design and control compressors for hybrid fuel cell-gas turbine (FC-GT) systems. In this study, compressor stall/surge analysis for a 4 MW locomotive hybrid solid oxide fuel cell-gas turbine (SOFC-GT) engine is performed based on a 1.7 MW multi-stage air compressor similar to available commercial compressors. Control strategies are designed and evaluated to prevent the operation of hybrid SOFC-GT beyond the stall/surge lines of the compressor. Computational fluid dynamics (CFD) tools are used to provide a better understanding of flow distribution and instabilities near the stall/surge line. Simulation results show the feasibility of using existing industrial compressors in the hybrid SOFC-GT system operation. The results show that a 1.7 MW system compressor like that of Kawasaki gas turbine is an appropriate choice among the industrial compressors to be used in a 4 MW locomotive SOFC-GT with topping cycle design.