Operation and energy savings in the separation of a twelve-cornponent hydrocarbon mixture by the pilot plant of an internally heat-integrated distillation column (HIDiC) were studied. Based on the operation results, a HIM simulator was developed using the commercial process-simulation software. The operation and simulation results showed that zero external reflux and zero reboiler heat duty operation were the most economical operation conditions, and that energy reduction of 62% compared to the conventional distillation column is achievable under these conditions. With the HIDiC simulator developed, a process flow involving heat exchange between the overhead vapor and the feed was Studied, and the possibility of further energy-saving operation of the HIDiC was suggested.