Hybrid solid oxide fuel cells–gas turbine systems for combined heat and power: A review

This paper presents a comprehensive review of the possible layout configurations of hybrid power plants based on the integration of solid oxide fuel cells (SOFC) and gas turbine (GT) technologies. SOFC/GT power plants have been investigated by using a plurality of approaches, such as: numerical simulations, experimental analyses, and thermo-economic optimizations. The majority of SOFC/GT hybrid systems are fed by methane, which is much cheaper and easier to manage than hydrogen. In fact, SOFC/GT systems use the capability of the fuel cell to internally perform the reforming process required to convert methane into hydrogen. The steam required to drive the reforming reaction can be supplied by the anode recirculated stream. Alternatively, such steam can be produced externally, by using the heat of the exhaust gases. In this case, steam can be used also for thermal purposes and/or for further system hybridization (e.g. Cheng cycle). The majority of the SOFC/GT power plants analyzed in literature are based on the pressurized arrangement, potentially able to ensure lower capital costs and higher efficiencies. Conversely, atmospheric plants are easier to manage, due to the possibility of operate the SOFC and the GT independently one of each other. The paper also investigates more complex SOFC/GT configurations, including: HAT turbines, IGCC SOFC/GT power plants, ORC cycles, etc. A detailed analysis of the SOFC/GT control strategies and part-load performance analyses is also presented, showing that such systems reach their best performance at nominal capacity, and are affected by significant reduction of the electrical efficiency in case of large variations of the load. Finally, the paper also presents a review of hybrid SOFC/GT power plants fed by alternative fuels, such as coal and biomass.