Spreadsheet to illustrate the application of relaxation methods for multicomponent distillation separations

Abstract

Rigorous calculation methods to simulate multicomponent distillation processes involve large number of variables and equations that are difficult to solve by hand and require the use of specific software. With this purpose, commercial process simulators have been included for years as learning tools in the syllabus of Chemical Engineering degrees. Nevertheless, there is thus a possibility of using these packages as a black box and strategies to mitigate that risk have been developed, as the use of spreadsheets where students can follow and check the calculation algorithms and the details of such calculations. One alternative to solve multicomponent distillation problems is the use of relaxation methods, that find the steady-state solution of a continuous distillation column by solving unsteady-state equations from a specified initial condition, thus providing an analogy with the column startup. In this work, a novel spreadsheet to apply a relaxation method is proposed. Calculation begins with the simulation of a distillation column at total reflux, which is a common way to start up these processes. In order to facilitate the development of unsteady-state equations and operation, a batch distillation column is also simulated. Finally, the evolution of a continuous distillation column from a specified starting condition to steady-state is simulated.