Carbon dioxide is essential to life on Earth, however its concentration in the atmosphere has significantly increased since pre-industrial era, causing global warming and climate change. To reduce these effects, the Paris Climate Agreement has established greenhouse gas emissions reduction targets, which can be achieved by decarbonizing energy-intensive industries as electricity production. Post-combustion removal of carbon dioxide can be obtained by employing aqueous solutions of amines - in most of the cases MonoEthanolAmine (MEA) is used - which absorb this acid gas from the flue gas streams and are then regenerated and recycled. They are widely employed, though being characterized by several drawbacks, as the high energy requirement at the reboiler of the regeneration section. Therefore, though adding Carbon Capture & Storage (CCS) to a power plant makes the production of electricity more advantageous from an environmental point of view, its operation represents an economic loss for the plant. Possible ways of minimizing the economic disadvantages due to the carbon dioxide removal section include running this section in flexible mode, on the basis of the price of electricity which varies from hour to hour and from day to day. The Capture Level Reduction (CLR) and the Solvent Storage (SS) methods are two possible solutions for flexible operation. This work focuses on the purification of a flue gas stream from a power plant fed with natural gas and performs simulations and techno-economic analyses of the CLR and SS modes, taking into account also the possible application of a carbon tax. By analysing the obtained results a comparison between the two options is carried out, and the best operating mode is determined.