Comparison between pressurized design and ambient pressure design of hybrid solid oxide fuel cell–gas turbine systems

Design performances of the hybrid solid oxide fuel cell (SOFC)–gas turbine (GT) system have been investigated. A pressurized system and an indirectly heated ambient pressure system were analyzed and their performances were compared. In the baseline layout, the basic performance characteristics of the two system configurations were analyzed, with the cell operation temperature and the pressure ratio as the main design parameters. The pressurized system exhibits a better efficiency owing to not only the higher cell voltage but also more effective utilization of gas turbine, i.e., a larger GT power contribution due to a higher turbine inlet temperature. Independent setting of the turbine inlet temperature was simulated by using the additional fuel supply as well as the air bypass. Increasing the pressure ratio of the gas turbine hardly improves the system efficiency, but the efficiency becomes less sensitive to the turbine inlet temperature. In the ambient pressure system, the available design parameter range is much reduced due to the limit on the recuperator temperature. In particular, design of the ambient pressure hybrid system with a gas turbine of a high pressure ratio does not seem quite feasible because the system efficiency that can be achieved at the possible design conditions is even lower than the efficiency of the SOFC only system.