Progress in solid oxide fuel cell-gas turbine hybrid power systems: System design and analysis, transient operation, controls and optimization

This paper presents a review of system design and analysis, and transient control and optimization of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems for different system configurations. The main feature of SOFC power systems is production of less harmful chemical and acoustic emissions at a higher efficiency compared to conventional power production technologies. Microturbines have been shown amenable to integration with a high temperature fuel cell due to the well-matched temperature and pressure characteristics of an SOFC and microturbine in a hybrid system. Different configurations of hybrid SOFC-GT systems are briefly discussed. The main focus of this paper is investigation of different control strategies and transient performance characteristics of hybrid SOFC-GT systems in the literature. Different control strategies including variable and fixed speed operation of shaft using PI control methods are discussed. Different types of bypass valves for hybrid system control such as recuperator bypass are used to control the inlet temperature of the air entering the stack. In addition, SOFC bypass valves are used to control the mass flow through the SOFC stack. Different control methods are described to avoid stall/surge in the compressor. The main components of a hybrid system and their effects on the system performance are thoroughly discussed. Impacts of heat exchangers on a hybrid system are also determined and pressure losses between the recuperator and combustor for three different conditions are evaluated. Effects of different system parameters such as Steam-to-Carbon ratio (S/C), fuel utilization and operating pressures on system performance are determined. Net efficiencies of different hybrid system configurations are compared. Other applications of a hybrid system such as those that include CO2 capture and sequestration are investigated. Finally, system optimization and investigation of alternative fuels are discussed.