Bridging retrofit feasibility and next-generation carbon capture: hybrid oxy-combustion strategies for micro gas turbines

Decarbonizing power generation requires carbon capture technologies that can be integrated into flexible, distributed energy systems such as micro gas turbines (mGTs). However, the low CO2 concentration in conventional mGT exhaust gases, typically below 5 mol%, makes post-combustion capture energy-intensive and costly. This study investigates oxygen-enriched combustion and full oxy-combustion as strategies to increase exhaust CO2 concentration and facilitate advanced hybrid cryogenic capture. Two mGT configurations are assessed: a conventional turbine retrofitted with exhaust gas recirculation (EGR) and oxygen enrichment, and a redesigned turbine optimized for oxy-combustion. These configurations are combined with two capture pathways: a hybrid Vacuum Pressure Swing Adsorption-Carbon Purification Unit (VPSA-CPU) for low-to-moderate CO2 concentrations, and a membrane-assisted CPU for higher concentrations. Simulation results show that the dry exhaust CO2 concentration can increase from 4 mol% under conventional operation to 87 mol% through combined EGR and oxygen enrichment. Although higher CO2 concentrations reduce power output and efficiency in the retrofitted system, the redesigned mGT reaches an electrical efficiency of approximately 18% under full oxy-combustion when capture and a representative oxygen-production penalty are included. Moreover, the specific energy consumption required to achieve 95% CO2 recovery decreases from 1317 kWh/tCO2 at 4.5 mol% to 125 kWh/tCO2 at 87 mol%. An optimal operating point depends on the balance among oxygen-production demand, capture energy consumption, turbine design, and oxygen-supply assumptions. These findings highlight oxy-combustion coupled with hybrid cryogenic capture as a promising route toward low-carbon, flexible, and dispatchable power generation.