The above stated energy saving potential can only be totally exploited by an optimally designed column. For this purpose, different possibilities have been developed in the literature. The simplest way is as described above. First specifications are added to Equation ( ) such that all degrees of freedom are fixed. A process simulator is used to solve the resulting system of equations. In an outer loop the specifications are modified until a satisfactory design is found. This is for example applied by . However, due to this outer loop the procedure requires significant calculation times.