Equal thermodynamic distance and equipartition of forces principles applied to binary distillation

Two theoretically derived entropy optimization methods for design of distil lation columns with multiple heat exchangers have recently been presented i n the literature. These two methods, called equal thermodynamic distance (E TD) and equipartition of forces (EoF), have here been applied to binary dis tillation and compared. For a 17 plate column separating benzene and toluen e the entropy production inside the ETD column was found to be 32.8% less t han the comparable adiabatic column while the entropy production in the EoF column was 32.6% less. A numerically calculated optimum was found to be 37 .3% better than the adiabatic column. The difference between the EoF column and the numerical optimum occurs mainly in the end sections where the EoF operating line requires driving forces which are difficult to obtain becaus e of the mass balance. The mismatch is mainly due to (i) failure to lake bu lk fluxes into account, (ii) mass balance restrictions on the driving force in the upper section, and (iii) uncertainty in the application of the Gibb s-Duhem equation. The ETD column differs from the numerical optimum much in the same manner as the EoF column, by requiring step sizes in the end sect ions which mass balance only allows at high entropy costs. For very large p late numbers, however, the ETD column is almost in complete agreement with the numerical optimum.