Synthesis Of Ethylene Cold-End Separation System

The design and operation of low-temperature distillation processes generallyinclude three sections: the core process (the separation sequence), the heat exchangernetwork (HEN) and the refrigeration system (RS). The traditional approach in practicefor the design of low-temperature processes begins with the design of the separationprocess; after that, the HEN is designed to recover heat, and finally, the refrigerationsystem is designed to support the former systems. And most existing research indistillation synthesis did not focus on low-temperature processes so that RS weredesigned separately in their work. Because the three parts of low-temperatureseparation system are interrelated, those methods above could not guarantee theminimum total cost.In this paper, a mixed-integer non-linear programing (MINLP) model was builtfor low-temperature processes, in which structures of separation sequences werepresented by integer variables and operating parameters were presented by continuousvariables. Unlike former researches, the process and corresponding HEN and RS werecarried out simultaneously in this work. Due to the adoption of the shaftwork targetmethod, the separation sequence synthesized in the paper could guarantee the lowestannual cost including RS compressor shaftwork consumption and capital cost ofdistillation columns without knowing any specific parameters for describing HEN andRS structures. Because the integer variables are not needed to describe HEN and RSstructure in the model, the scale of the model is largely reduced, and the solutionprocedure is more simple and efficient. The model was applied in an ethylene coldend separation case and significantly reduced the total annual cost.