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As fossil fuel power plants have emitted significant quantity of carbon dioxide (CO2) into the atmosphere which aggravates climate change, capturing and storing such emissions is key to mitigate the issue. An adsorption system based on a physical adsorbent i.e. activated carbon is first assessed to capture CO2 emissions from a natural gas combined cycle. Then a subcritical sequential supplementary firing combined cycle with CO2 capture is used to analyse the effect of CO2 concentration. Analyses are carried out in terms of power loss and thermal efficiency. To evaluate the advantages of post-combustion CO2 capture using activated carbon, results are compared with systems using a commercial absorbent, i.e. monoethanolamine and a chemical adsorbent i.e. polyethyleneimine/silica. The net efficiency of natural gas combined cycle using activated carbon increases slightly from 50.8% to 51.1% due to the lower regeneration temperature at 358 K. The performance of the system using PEI/silica is almost the same as that using activated carbon at 368 K. Although the thermal energy required to regenerate the activated carbon is relatively high, a significant improvement of net efficiency is observed with increased partial pressure. Economic analysis indicates that the systems using activated carbon is a competitive alternative for CO2 capture. It is concluded activated carbon is relatively more advantageous than monoethanolamine in terms of efficiency and cost, which could be further improved with enhanced heat and mass recovery.