Retrofit of complex and energy intensive processes

Sequential structural and parameter optimization of retrofitted complex and energy intensive continuous processes has been studied. A method for sequential optimization of retrofits, combined sequential approach has been developed using pinch analysis, an improved optimization procedure and mixed integer nonlinear programming (MINLP) or nonlinear programming (NLP) algorithms. Pinch analysis gives many alternative retrofit designs for postulating a superstructure. The superstructure, material and energy flow rates have been optimized sequentially by a direct search method using ASPEN PLUS simulator with energy and material bounds. The heat exchanger network of the superstructure obtained, flashes and compressor were optimized simultaneously with the MINLP or NLP algorithms. We have realized an additional profit of 2,803 MUSD/yr with the combined sequential approach in a case study of an existing methanol plant.