Performance analysis of coal gasification processes integrated with high temperature fuel cells and gas turbine hybrid power plants

High temperature fuel cells (Solid Oxide Fuel Cells, SOFC, and Molten Carbonate Fuels Cell, MCFC) appear to be one of the most promising options for power generation, mainly because of their very high conversion efficiency and extremely low polluting emissions. In particular, SOFC and MCFC are of special interest with hybrid configurations where the fuel cells are integrated with a gas turbine system. The hybrid systems currently developed are mainly fuelled with natural gas, but they can also be fuelled with syngas from coal or biomass gasification. The Department of Mechanical Engineering of the University of Cagliari (DIMECA) is involved, together with some institutional and industrial partners (ENEA, Sotacarbo, Ansaldo Ricerche, CSM, et al.) in some RTD projects for the development of near zero emission technologies for coal utilization with combined production of hydrogen and electricity in distributed power generation. In this context, Sotacarbo is developing an integrated gasification process, based on a fixed-bed (updraft) gasifier, to be used in medium- and small-scale commercial plants. Among the different options under evaluation for the power generation section, particular attention has been devoted to SOFC-GT and MCFC-GT hybrid systems. For this reason, in this paper, a performance assessment of fixed-bed coal gasifiers integrated with MCFC and SOFC hybrid power plants has been carried out. A comparative performance analysis between hybrid systems fuelled by natural gas and coal gas has also been included. The performance analysis carried out in this paper demonstrates that integrated gasification and high temperature fuel cell systems (IG-MCFC and IG-SOFC) may be an interesting option for power generation. In fact, the IG-SOFC plants considered herein show efficiency values exceeding 46%. On the contrary, small- and medium-size IG-MCFC power plants can achieve efficiency values of around 38%. Moreover, the study points out that replacing methane with coal gas reduces stack efficiency by about 11 percentage points for MCFC and by about 12 percentage points for SOFC (from 48-49% to 36-37% for both fuel cells) and overall hybrid plant efficiency by about 8-9 percentage points