Mitigating CO2 emissions is an important clean energy research topic. Post-combustion carbon capture is a well established and vital carbon capture technology for existing fossil-fueled power plants. In this work, monoethanolamine (MEA) based carbon capturing unit was designed using AspenPlus V.10 software for a 300 MWe power unit of Mae Moh power plant in Thailand. Technical and economic analysis of retrofitting a lean aqueous MEA system was investigated. From the simulation study, it was revealed that the optimal lean CO2 feeding for the amine-based carbon separation plant was about 0.2 mol/mol using packed columns with Sulzer Mellapak 250Y product. The optimal liquid-to-gas ratio with a flue gas containing 15% CO2 was approximately 3.0. Furthermore, the optimal total costs of the plants were less than 55 $/ton of CO2 captured.