Process modelling, optimisation and analysis of heat recovery energy system for petrochemical industry

The petrochemical industry is an energy-intensive process. Heat exchanger network (HEN) is widely applied in existing petrochemical plants used to save energy. However, there is still some amount of low-grade heat wasted. No mathematical model can directly tackle the problems with majority of phase-changing process streams. Therefore, this study aims to optimise an extended low-grade heat recovery model for the petrochemical plant by integrating the organic Rankine cycle (ORC) with HEN. A mixed-integer nonlinear programming steady-state model was first developed. Then, the ORC operation conditions were optimised simultaneously. Finally, the thermodynamics (energy and exergy) and economic analysis were performed to evaluate the system performance, with 41 MW more heat recovered, 2.01% higher exergy efficiency and 3219 k$/year less total annual cost, compared with HEN only. Furthermore, the optimisation results indicate that the proposed energy system performs with 386 MW of recovered heat from the process streams, 82.13% of the overall exergy efficiency, 3.94 MW of net power generated from ORC, and 4416 k$/year of electricity profit. Research presented in this paper hopes to shed light on design and operation of the petrochemical industry for energy savings and cost reduction.