For the improvement of distillation column efficiency, a new system of a fully thermally coupled distillation column is proposed and its performance is examined with two industrial processes. The system has an extra column called postfractionator and attached to the main column of an original fully thermally coupled distillation column. The outcome of performance investigation indicates that a 29% energy saving is yielded with fractionation process and a 7% saving with gas concentration process over the original fully thermally coupled distillation column. The design detail of the new system is explained, and the increase of distillation column efficiency is discussed. In addition, some considerations on the new column construction, such as arrangement of distillation column sections and divided wall construction, are discussed here. (c) 2005 Elsevier B.V. All rights reserved.