Heat Exchanger Networks Retrofitted with Simultaneous Pressure Recovery

This paper presents a new optimization model for the retrofit of heat exchanger networks (HENs), in which the pressure recovery of streams is used to enhance heat integration. Especially important in sub-ambient processes, the HEN retrofit with pressure recovery is mainly aimed at reducing the usage of expensive cold utility. The proposed superstructure allows the increment of the existing heat exchange area, and the use of new equipment for both heat exchange and pressure manipulation. The pressure recovery of streams is performed simultaneously with the HEN synthesis, such that the process conditions are optimization variables. The model based on a mixed-integer nonlinear programming formulation considers the coupling of turbine and compressor with a helper motor, in order to minimize the total annualized cost composed by additional capital and operational expenses. The results indicate that the pressure recovery is essential for decreasing the total cost of the HEN retrofit.