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Dividing-wall column (DWC) is a promising thermally coupled distillation technology for separating multicomponent mixtures. However, the difficulty of controlling vapor split ratio in DWC affects its energy consumption and so limits its wider application in industrial practice. The liquid-only side-stream distillation (LSD) process not only eliminates the vapor split in DWC but also shows comparable economic and thermodynamic efficiency with DWC. This study systematically optimizes and compares the economic performance of DWC and double LSD (DLSD) process for separating ethanol-propanol-butanol ternary mixture, and then analyzes exergy flows in these two processes in detail. Results indicate that TAC of DLSD process is 11.47% lower than that of DWC process, and exergy efficiency of DLSD and DWC processes is 10.81% and 8.57%, respectively. However, both processes exhibit similar exergy destruction in condensers, columns, coolers and reboilers. • Double liquid-only side-stream distillation (DLSD) and dividing-wall column (DWC) are presented and optimized. • Both economic assessment and exergy analysis of DLSD and DWC are carried out. • DLSD has lower annual total cost and higher efficiency than DWC. • DWC and DLSD exhibit similar exergy destruction distributions in columns and heat exchangers. [ABSTRACT FROM AUTHOR]

• Double liquid-only side-stream distillation (DLSD) for separating ethanol, n -propanol and n -butanol mixture. • Temperature control schemes without composition measurement for DLSD are proposed. • Single temperature control (STC) and temperature difference control (TDC) for DLSD are compared. • TDC with feedforward action has better performance by a factor of 5 or more in total integral absolute error. The investigation of dynamic controllability of double liquid-only side-stream distillation (DLSD) is necessary due to its good potential for separating multicomponent mixtures in industrial practice. However, control strategy for DLSD is unique and complex owing to the existence of liquid side transfer streams. This study proposed three temperature control schemes without composition measurement for DLSD, i.e., single temperature control without feedforward structure (CS1), single temperature control and temperature difference control with feedforward structure (CS2 and CS3). Results demonstrate that DLSD process can be operated smoothly under ±20% feed flow rate and composition disturbances. The use of feedforward structure in CS2 and CS3 eliminates the transient deviations in the responses of product purities in CS1. Overall, CS3 provides better control for DLSD than CS1 and CS2 in terms of lower total sum of integral absolute error (by a factor of nearly 50 and 10, respectively). [ABSTRACT FROM AUTHOR]