In Level 1, the sub-systems are modelled in different dedicated simulators. The two NGCC power plants are represented in Integrated Environmental Control Model (IECM). MEA absorption is also modelled in IECM. The PSA is modelled in Dymola, which is a mature and broadly deployed tool for modelling dynamic processes. In Level 3, surrogate-based optimization is performed, as illustrated in Figure . We deploy a simulation-based optimization approach, where simulation is executed within the optimizer.