Design optimization and control of dividing wall column for purification of trichlorosilane

Abstract

• TA C appr . is proposed as a novel objective function for DWC parameter optimization. • Optimal energy control structure can be achieved by manipulating liquid split ratio. • MPC-PI hybrid structure balances both control performance and safety performance. • Simulated annealing algorithm is employed to optimize the weights of MPC controller. Polysilicon quality and energy consumption are directly affected by the purification process of trichlorosilane. In this work, the dividing wall column (DWC) as a promising energy-saving technology is utilized for trichlorosilane purification, with the design optimization carried out using steady-state simulation. Compared with conventional distillation process, DWC can reduce total annual cost (TAC), CO 2 emissions and exergy loss ( El ) by 35.81%, 53.56% and 54.10% on average, respectively. Established on the characteristics of superfractionator, four control structures are proposed in this work, two of which are multi-loop proportional-integral (PI) control schemes including condenser duty ( C ), distillate flow rate ( D ), bottom flow rate ( B )/reflux flow rate ( R ), side flow rate ( S ), reboiler duty ( V ) control structure and optimal energy control structure. The other two are model predictive control (MPC) schemes including standard MPC structure and MPC-PI hybrid structure. The weights of MPC controller are optimized using the simulated annealing (SA) algorithm. Dynamic simulation results demonstrate that MPC schemes achieve improved closed-loop performance in terms of minor overshoot, shorter transition time and reduced oscillation than PI control schemes. The integral absolute error (IAE) is introduced to further quantitatively evaluate MPC schemes. The simulation results demonstrate that the standard MPC structure achieves the best control performance and the MPC-PI hybrid structure enhances process safety while maintaining the desired control performance.