Circular integration (CI) of crude distillation unit (CDU) is introduced the closed loop to recover waste heat from hot product streams to heat the cold crude steams and reduce the external energy resulting in lower CO2 emission and utilities cost saving. The stagewise superstructure by Yee and Grossmann (1990) is applied to retrofit heat exchanger network (HEN) of crude preheat train supported by variable heat capacity as a function of temperature. The objective function for HENS is to maximize Net Present Value (NPV) of retrofitted HEN which relates to maximizing utilities cost saving. The optimization problem is solved by using General Algebraic Modelling System (GAMS) with DICOPT optimization solver. The HEN retrofit result shows that this model can reduce 65.44% of CO2 emission and achieve 12,584,244.74 $ of NPV.
