Waste-Heat and Cold-Exergy Recovery in an Integrated CAES–ORC–LNG Energy System

This study presents an integrated diabatic compressed air energy storage (D-CAES)–cascade organic Rankine cycle (ORC)–liquefied natural gas (LNG) polygeneration system that simultaneously delivers electricity, district cooling, and pipeline-grade natural gas. The D-CAES turbine exhaust serves as the primary heat source for a cascade ORC employing a zeotropic working-fluid mixture, while the LNG warming curve provides a cryogenic condensation sink uniquely suited to glide-matched condensation of the zeotropic condenser. A four-criterion (4E) framework is applied at the component level, yielding four global performance metrics: exergy round-trip efficiency (ERTE), total annualized cost rate (Żtot), CO2 emission factor (ζCO2), and net discharge power. A surrogate-assisted multi-objective optimization is developed in which 1000 Latin-hypercube-sampled high-fidelity simulations train three independent artificial neural network (ANN) surrogate models, which are then coupled with the optimization algorithm. The TOPSIS-selected compromise solution achieves an ERTE of 47.55%, a total cost rate of 293.75 USD h−1, and a CO2 emission factor of 166.98 kg MWh−1. Sensitivity analysis demonstrates that turbine inlet temperature and charging pressure are the dominant thermoeconomic drivers.