A multi-objective reactive distillation optimization model for Fischer–Tropsch synthesis. (6th April 2020)

• Record Type: Journal Article
• Authors: Zhang, Yizu; He, Naien; Masuku, Cornelius M.; Biegler, Lorenz T.
• Is Part Of: Computers & chemical engineering. Volume 135(2020)
• Publication Date: 2020-04-06
• Subjects: Equation-oriented optimization framework -- Mathematical programming with complementarity constraints -- Multi-objective optimization -- Low temperature Fischer–Tropsch -- Process intensification; Chemical engineering -- Data processing -- Periodicals; 660.0285
• DOI: 10.1016/j.compchemeng.2020.106754
• Languages: English
• ISSNs: 0098-1354

Abstract

Highlights: Equation oriented optimization model developed for reactive distillation with low temperature Fischer–Tropsch. Problem formulation includes complementarity constraints to handle phase disappearance as well as tray optimization. Multi-objective optimization strategy is applied to balance maximization of wax flow rate, naphtha purity and diesel purity. Abstract: In the design of a reactive distillation column, aspects such as column configuration, catalyst loading, tray temperature, and side extraction rates should be well considered. Though preferences in Fischer–Tropsch (FT) synthesis may vary, it is acknowledged that the final product contains a wide range of hydrocarbons including fuel gas, gasoline, diesel, and linear wax. Zhang et al. (2018) previously developed an equation-oriented framework for optimal synthesis of integrated reactive distillation systems for FT processes. Here, we extend the mass, equilibrium, summation, and heat equations to a mathematical program with complementarity constraints to deal with possible dry trays in the non-reactive sections. The purpose of describing disappearing phases is to avoid infeasibilities due to multiple bilinear terms in the model for complicated model structures. The model is implemented by solving initialization steps and a sequence of nonlinear programming problems to determine an optimal structure and operating conditions. Design specifications for multiple products could be set as individual objectives to determine design limits. Moreover, a balance of multiple objectives could be reached by formulating the reactive distillation model as a multi-objective optimization problem. In this work, we employ the augmented ϵ-constraint method. The results show that significant design insights can be gained from the Pareto-optimal front regarding acceptable trade-offs among various objectives.