Multistream heat exchangers (MHEXs) find application in a variety of energy intensive cryogenic processes. However, simultaneous optimization of process and MHEXs is often hindered by its nonlinear behavior and combinatory difficulties, which lead to low computational efficiency and poor solution qualities. In this paper, we present a mixed-integer nonlinear programming (MINLP) framework that comprises heat recovery of MHEXs, thermodynamics, vapor-liquid equilibrium, and other unit operations of the process. The MHEXs model combines the concept of Pinch analysis and multi-M formulation that improves solution efficiency by reducing the number of binary variables and nonconveixty of the model. The framework is applied to an industrial air separation unit (ASU) with multiple MHEXs to demonstrate its effectiveness.
