In this paper the results of the thermodynamic and economic analyses of large size power plants (450 MWe ) and distributed power plants (1.5 MWe ) are compared and described. The work is focused on the decarbonization of natural gas through a CO2 separation unit, which employs a technology (amine chemical absorption) viable for short-term implementation in real installations. Plant layouts, analyzed in previous open literature works, were taken as references. The plants proposed in this paper are seven: three belong to large-scale centralized electricity production while the remaining four belong to distributed power generation. The first three consist of: 1- a Combined Cycle fed by natural gas; 2- a Combined Cycle fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes; 3- a Combined Cycle fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes including a more detailed mathematical model of the CO2 separation unit that properly considers the amount of steam needed by the stripping towers. Four different power plants solutions are proposed for the Distributed Generation: 1- a simple cycle gas turbine fed by natural gas; 2- a Hybrid System with tubular SOFC fed by natural gas with internal reforming; 3- a 1.5 MWe gas turbine fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes; 4- Hybrid System fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes. The results were obtained with WTEMP software, developed by the TPG of the University of Genoa, and showed that the thermodynamic and economic impact of the adoption of zero-emission cycle layouts is relevant: advanced alternative technologies, such membrane-based separation units, are highly desirable to improve plant performance.