Selecting suitable energy-saving distillation schemes: Making quick decisions

More and more frequently, chemical engineers need to make quick decisions when selecting suitable energy-saving distillation schemes, for example, choosing between double effect and heat pump. Having endured this situation for years, the authors try to introduce, in this paper, shortcut methods to help choose between heat pump-assisted distillation and multi-effect distillation by evaluating energy efficiency in comparison with a conventional distillation column without any heat integration. To verify the accuracy of the shortcut methods, five binary systems with different relative volatilities, namely, methyltrichlorosilane-dimethyldichlorosilane, 2-methylbutane-n-pentane, benzene-toluene, methanol-water and cyclohexane-cyclohexanol, are studied using the shortcut methods with the aid of rigorous simulations. The energy efficiency results are presented in terms of standard oil versus atmospheric relative volatilities for both double-effect distillation and mechanical vapor recompression assisted distillation. Systems with lower relative volatilities perform best with the heat pump option, while systems with higher relative volatilities perform better with heat integration. The aim of the shortcut methods—to simplify and speed up the decision using only easily accessible data such as relative volatility and utility prices—is achieved.