The reduction of carbon dioxide from the flue gases of a semi-closed gas turbine combined cycle (SCGT/CC) by means of absorption in ammonia aqueous solutions has been studied. The absorption system has been simulated by means of Aspen PlusTM. The main variables of the removal system have been varied in order to understand their influence on system performance. With reference to the SCGT/CC case study, the removal of CO2, considering a removal efficiency of 89%, dramatically decreases the overall cycle efficiency from 53 to 41%, with the main contribution to this decrease being due to the power consumption for flue gas compression up to the absorption unit pressure. CO2 specific emissions pass from 390 to 57 kg/MWh.