(290e) Remixing Control for Divided-Wall Columns

The divided-wall column is an energy-saving promising technology for the separation of ternary mixtures, but the control is difficult because of its complexity structure and interactions of control loops. Although a few control methods have been provided up to now, the general control method for all ternary mixtures is still pending because of the difference of relative volatilities. In this work, we explore a new structure by controlling the remixing of the intermediate at the top trays in prefractionator section for the separation of benzene, toluene, and o-xylene. It is found that avoiding the remixing of intermediate compound toluene helps divided-wall column working very close to the optimal conditions. The remixing of the intermediate compound in the divided-wall column is studied at steady state first. Then, a remixing control structure with four composition control loops is presented. Minimizes energy consumption is achieved by avoiding the remixing of intermediate compound at the top of the prefractionator. 20% disturbances in feed flow rate and feed composition are used to demonstrate the effectiveness of the proposed control structure. Remixing profile analysis of intermediate compounds in ternary mixture gives an easy and new way to design and control the divided-wall column at energy saving conditions.