Dynamic control investigation of an energy-saving double-thermally coupled ternary extractive distillation process

•Dynamic control of the double-thermally coupled extractive distillation process is studied.•Newly robust control schemes are developed for this highly integrated configuration.•Dynamic performance is improved by robustly manipulating the splitting vapor flowrate.•±20 % large disturbances in throughput and feed composition are effectively handled.•Oscillations are eliminated by adjusting position of temperature-composition cascade control. Currently, little literature has focused on the dynamic control of the economic and energy-saving double-thermally coupled ternary extraction distillation (DTCTED) systems, which demonstrates difficulties due to complex interactions between the main column and two rectifiers. The novel contribution of this paper is proposing effective and robust control structures to improve the dynamic controllability of the DTCTED process. To maintain the product purities more precisely, the key control loops employ composition-temperature cascade controls to regulate the side-vapor flowrates because the reliance on temperature control alone (CS1) is insufficient. Although this structure (CS2) can achieve the control of product purity, there could be severe oscillation in the control process. Therefore, one of the composition-temperature cascade controls is paired with the reflux ratio of the side rectifier to relax the operating freedom of the main column. The obtained structure (CS3) can brilliantly handle ±20 % throughput and various feed composition disturbances, which ensures the product purities and reduces oscillation. Additionally, control strategies based on the relative gain array (RGA) pairing criterion are explored and compared with the empirical ones. The proposed structures significantly enhance the controllability and stability of the DTCTED process, making it highly suitable for industrial applications.