The design procedure developed for a new type of heat-integrated distillation column was verified through the operation data of a commercial plant. In a conventional heat-integrated distillation column (HIDiC), optimal heat exchange cannot be achieved because the heat exchange between the rectifying section and the stripping section is executed through the wall at the same elevation physically. We have proposed a new process structure in which the heat exchange is executed between several pairs of stages in the rectifying and stripping sections; such a heat-integrated distillation column is hereafter called the discrete HIDiC (D-HIDiC). The energy-saving performance of D-HIDiC depends on the compositions to supply/remove the heat, the selection of the pair of stages to be heat-exchanged and the amount of heat transferred at each heat exchanger. We have developed a new graphical design procedure for D-HIDiC, in which a plausible design is interactively derived by using H-xy and T-xy diagram that is an extension of Ponchon-Savarit H-xy diagram. The proposed design procedure was applied to a design problem of a commercially operating column at Maruzen Petrochemical, Japan, and the existing column was replaced with a newly installed D-HIDiC. Through stable operation since August in 2016, it was verified that more than 55% energy conservation to the conventional distillation column could be achieved. In this paper, further energy conservation by modifying the operation condition is discussed. The heat allocations to side heat exchangers have been changed by referring to the design result on the proposed H-xy and T-xy diagram. As the adiabatic efficiency of the compressor was decreased in comparison to the original operation mode, the improvement of energy-saving was not so large. However, assuming the same adiabatic efficiency of the compressor, the simulation result has shown much better energy conservation compared to the original operation mode. Real operation data and simulation result demonstrated that the appropriate side heat exchanger allocation could achieve higher energy conservation. It was also verified that the direction of better operating condition can be obtained from the proposed design procedure by using H-xy and T-xy diagram. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.