Numerical optimization of heat recovery steam cycles: Mathematical model, two-stage algorithm and applications

Most of the advanced integrated energy systems need a heat recovery steam cycle (HRSC), either fired or unfired, that recovers the waste heat from gas turbines and process units in order to generate electric power and supply mechanical power to compressors, heat to endothermic processes, and steam to external users. The key feature of such HRSCs is the integration between the heat recovery steam generator (HRSG) and the external heat exchangers. This paper presents a rigorous mathematical programming model, a linear approximation, and a two-stage algorithm for optimizing the design of integrated HRSGs and HRSCs, simultaneously considering the HRSG together with the heat recovery steam network and the intensive steam cycle variables. A detailed application of the methodology is described for an integrated gasification combined cycle plant with CO2 capture and results for other interesting plants are reported. A significant efficiency gain is obtained with respect to usual practice designs.

► We present a methodology for optimizing the design of integrated HRSCs and HRSGs.
► HRSG, steam network and intensive variables of the cycle are simultaneously optimized.
► An accurate linear approximation of the resulting discontinuous NLP is proposed.
► A two-stage algorithm based on linear programming and particle swarm is developed.
► A significant gain in efficiency gain is observed for several integrated plants (e.g., IGCCs).