Minimum Number of Transfer Units and Reboiler Duty

12 Some guidelines to evaluate distillation columns, considering only basic 13 thermodynamic data and principles, are provided in this paper. The method allows a 14 first insight to the problem by simple calculations, without requiring column variables 15 to ensure rational use of energy and low environmental impact. The separation system is 16 approached by two complementary ways: minimum and infinite reflux flow rate. The 17 minimum reflux provides the minimum energy requirements, and the infinite reflux 18 provides the feasibility conditions. The difficulty of separation can be expressed in 19 terms of number of transfer units (NTU). The applicability of the method is not 20 mathematically limited by the number of components in the mixture. Several mixtures 21 are rigorously simulated as illustrative examples, to verify the applicability of the 22 approach. The separation of the mixtures, performed by distillation columns, is feasible 23 if a minimum NTU can be calculated between the distillate and bottom compositions. 24 Once verified the feasibility of the separation, the maximum thermal efficiency depends 25 only on boiling point of bottom and distillate streams. The minimum energy 1 requirements corresponding to the reboiler can be calculated from the maximum 2 thermal efficiency, and the variation of entropy and enthalpy of mixing the distillate and 3 bottom streams. 4 5