A methodology of process intensification was discussed through the concept of "detuning" from the ideal state, especially for the energysaving continuous distillation processes, which are typical energy consumer in the chemical and petrochemical industries. First, the reversible distillation was shown as the thermodynamically ideal state. Then, it was indicated that several energy efficient modifications of distillation processes can be obtained by "detuning" or simplifying the reversible system. Among these modifications, an internally heat-integrated distillation column (HIDiC) was one of the most promising options. The development of the HIDiC in the national projects was reviewed and the reduction of energy consumption by the HIDiC was estimated to be 60 % of the conventional column from the results of the projects.