Optimal operation mode switching of dividing wall distillation based on model-predictive control

Abstract

Dividing wall distillation(DWC) column is becoming a new standard of separating and purifying multivariate mixed liquid, because of DWC represents that forced operation will play a role in separation technology, which have high energy efficiency and compact structure. DWC is composed of a lot of equipments of diversified configurations, so it is complicated to operate process and requirements for specific or advanced control system technology. When operation objectives of DWC need to be online conversion, operation will be not smooth, etc.. In order to solve these problems, we used two-layer control structure. The bottom layer was basic control layer(PID) and model-predictive control(MPC), and the top layer was predictive functional control(PFC) or fast model-predictive control(FMPC) which can realize operation optimizing function. The main objective is to achieve a smooth transition between the optimal mode switching and to ensure optimum goal can be realized. By implementation of proposed operating strategy in a four-component mixture Kaible column, the simulation results showed that this new method was feasible and concise.

Numerical and Experimental Research on a Kaibel Divided-Wall Column: Design and Steady-State and Dynamic Operation

“…KDWC exhibits a great potential industrial application prospect for the separation of a four-component mixture because of its relatively simple structure and cost savings. Thus, great efforts have focused on the operability and controllability of the KDWC. − Strandberg et al investigated the stabilizing control of a KDWC by maximizing the product purity with fixed energy usage, and the liquid split ratio was found to have an impact on the column’s sensitivity to disturbances. Two operating schemes, minimizing the vapor flow rate at fixed product purities ( J = V ) and maximizing the product purities with fixed boilup rate ( J = D (1 – x D ) + S 1 (1 – x S 1 ) + S 2 (1 – x S 2 ) + B (1 – x B )), were compared to control a KDWC in Ghadrdan et al.’s work .…”

“…In addition to the traditional single-loop PID controller used in the aforementioned literature, model-predictive control (MPC) was also applied to KDWC control . Furthermore, a two-layer control structure that combines PID and MPC and fast model-predictive control (FMPC) were utilized for KDWC control . Skogestad’s group built a laboratory-scale KDWC and experimentally studied its steady-state operation.…”

“…36 Furthermore, a two-layer control structure that combines PID and MPC and fast model-predictive control (FMPC) were utilized for KDWC control. 44 Skogestad's group 45 built a laboratory-scale KDWC and experimentally studied its steadystate operation. The experimental data were compared with model values for operation under two optimal modes, which showed that steady-state operation was close to the optimal scenario, although the upper side and lower side products had low purity.…”