Thermodynamic analysis of oxy-fuel combustion power cycle

Abstract

The oxy-fuel combustion power cycle (OFPC) based on the Allam cycle with supercritical carbon dioxide is a promising technology for reducing greenhouse gas emissions. While current literature estimates its efficiency with natural gas between 48% and 62%, the impact of the power unit's electrical power capacity on overall efficiency remains underexplored. This study investigates how supplied power affects OFPC net efficiency through preliminary thermodynamic parameter optimization. A comprehensive mathematical model of the OFPC was developed using the Aspen software package. The model integrates key subsystems: a gas turbine unit, cooler-separator, air separation unit, and compressor-storage unit. The modeling results indicate that lowering the working fluid temperature at the cooler-separator outlet to 17 °C boosts the maximum net cycle efficiency to between 51.16% and 53.1%, assuming complete moisture removal in the cooler-separator. Furthermore, a quantitative assessment of the scale effect shows significant benefits from increasing capacity. Scaling the supplied capacity from 50 MW to 800 MW reduces the specific electricity consumption for auxiliary power needs by 37.6%, achieving 1.12 kW/kg O2. In conclusion, utilizing higher-capacity equipment in the OFPC is both technologically and energetically justified. Increasing the supplied capacity from 50 MW to 800 MW effectively increases the overall net efficiency of the Allam cycle by 1.97%.