Simultaneous optimization of energy and materials based on heat exchanger network simulation for diesel hydrotreating units

A multi-period nonlinear programming (NLP) formulation is presented in this paper. This is intended to optimize energy and materials simultaneously for diesel hydrotreating units in order to minimize the total costs which include product income, material cost, energy cost, and other fixed operating costs. The heat exchanger network (HEN) is integrated into the model to address the energy consumption changes with the stream flow and temperature of different production modes. Some process models are regressed from production data or are supplied by refinery engineers, similar to the models for steam turbines and compressors, and distillation towers. An iterative algorithm is developed to solve the complex mathematical model based on HEN simulation. An industrial diesel hydrotreating unit is provided by the Chinese Refinery Complex and is used to demonstrate the performance of the formulated model and algorithm. It is found that the optimized results from the simultaneous consideration of the energy and materials are more profitable than those obtained from other methods that individually optimized the energy or materials. (C) 2009 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.