Thermodynamic Assessment of Oxy-Fuel Retrofit with Flue Gas Recycle in a Subcritical Coal Power Plant

Abstract

Achieving net zero emissions targets requires deep decarbonization of coal-fired power plants, particularly in countries like Indonesia where coal remains dominant in the electricity mix. As early plant retirement poses risks to energy security, retrofit solutions such as oxy-fuel combustion offer a transitional pathway. This study investigates the thermal feasibility of oxy-fuel combustion with wet flue gas recycle applied to a subcritical pulverized coal plant, using Suralaya Unit 8 (625 MW) as a reference case. A steady-state Aspen Plus model is developed to compare air-fired and oxy-fuel scenarios, with oxygen mass flow fixed and the flue gas recycle tuned to match flue gas heat capacity. Results show that the oxy-fuel case maintains equivalent gross output (560.95 MW) and boiler efficiency (83.21%) while exhibiting higher adiabatic flame (1,652.8°C) and furnace exit temperatures (1,283.4°C), increasing slagging risk. The flue gas outlet temperature rises sharply to 389.7°C due to air preheater bypass, underscoring the need for flue gas cooling or heat recovery systems to protect downstream units. Gas composition analysis reveals significant enrichment in CO₂ (46.1%) and H₂O, along with lower volumetric flow and density, which may allow repurposing of air-side fans and partially offset the ASU energy penalty (~82.6 MW).