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

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), CO2 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.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

In this study, the dividing wall column (DWC) was utilized for trichlorosilane purification as a promising energy-saving technology, with design optimization carried out using steady-state simulation. Compared to traditional distillation processes, DWC can significantly reduce total annual cost, CO2 emissions, and exergy loss. Four control structures were proposed, with model predictive control (MPC) schemes showing improved closed-loop performance in terms of overshoot, transition time, and oscillation reduction.