Next Generation Turbo-Expander-Based Cryogenic Purification Technology for Oxy-Fuel Combustion Capture

Abstract The decarbonisation of fossil-fuel-based energy systems, particularly in the power generation sector, is essential to achieving global climate targets. Oxy-fuel combustion, which involves burning fuel with oxygen-enriched air instead of atmospheric air, generates a flue gas stream primarily composed of CO2 and H2O, making downstream separation more energy-efficient. However, the high energy demand of the air separation unit (ASU) and the intensive utilities required for cryogenic CO2 purification limit the overall efficiency and viability of oxy-fuel capture systems. To address these challenges, this study investigates a next-generation solution—a turbo-expander-based cryogenic distillation system (hereafter referred to as CryoDT) originally developed for high-CO2 natural gas processing. The CryoDT system has been adapted to the oxy-fuel combustion context, aiming to reduce energy consumption and improve process efficiency by recovering energy from internal process streams rather than relying solely on external utilities. A key feature of the system is the integration of a turbo-expander, which simultaneously depressurises and cools the gas stream while recovering energy and the use of captured CO2 as an internal refrigerant for feed gas pre-cooling. Process simulations were conducted using Aspen HYSYS v14 with the Peng–Robinson EoS, while P-HENS was employed to generate and evaluate optimal and near-optimal heat exchanger network (HEN) designs. Over 50 feasible HEN structures were evaluated, with Structure #3 selected as the optimal configuration based on total annualized cost (TAC), spatial footprint and maintenance simplicity. Further improvements were achieved by internally utilising cold energy from Crude Liquid Oxygen (CLOX), which reduced the pre-cooler duty by 83.3%. The study highlights a key trade-off between ASU energy consumption and cryogenic purification load, identifying an optimal oxygen purity of 80 mol.% as the best balance. The integrated system achieved approximately 90% CO2 capture efficiency with a projected 35% reduction in overall energy penalty compared to conventional systems. This research demonstrates that CryoDT offers a technically viable and energy-efficient path forward for oxy-fuel CO2 purification. The results provide a solid foundation for further techno-economic and safety studies to benchmark CryoDT against conventional technologies.