Thermodynamic comparison of cryogenic air separation units with external and internal compression of oxygen designed for the coal-fueled Allam cycle

Coal-fueled Allam cycle is an advanced supercritical CO2 power cycle characterized by near-zero carbon emissions and high thermodynamic efficiency, which critically relies on the efficient oxygen supply from the cryogenic air separation unit (ASU) for coal gasification and syngas combustion. This study conducts detailed modeling and comprehensive thermodynamic analysis of ASU models with external compression (EC) and internal compression (IC) of oxygen production at high pressure. Energy consumption and exergy distribution of two ASU models and their coupling systems with the coal-fueled Allam cycle are evaluated with/without heat integration of the air compression process. Results show that the EC model has a lower specific energy consumption (0.497 kWh/kg) compared to the IC model (0.524 kWh/kg) with intercooled compression of feed air. Nevertheless, the thermal exergy recovered from the IC (67.50 MW) is much higher than that of the EC (32.89 MW) under the adiabatic compression condition. With heat integration between ASU and Allam cycle, the IC-Allam system achieves the highest net efficiency of 46.70 %, 0.86 % points higher than that of the EC-Allam system (45.84 %). These findings highlight the potential for optimizing overall system performance and net efficiency by integrating the ASU using oxygen internal compression and air adiabatic compression with the coal-fueled Allam cycle.