The influence of tangent pinch points on the energy demand of batch distillations: development of a conceptual model for binary mixtures

TORRES, KARINA ANDREA; ESPINOSA, JOSÉ

INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH

AMER CHEMICAL SOC

Año: 2011 vol. 50 p. 6260 - 6275

0888-5885

This contribution explores the influence of tangent pinch points on the performance of batch distillations of highly nonideal binary mixtures and its incorporation into a conceptual modeling framework under the assumption of a rectifier with an infinite number of stages. First of all, the y-x diagram is divided into three regions taking into account both the inflection point (IP) in the phase diagram and the slope of the equilibrium curve at . After that, limiting values for the reflux ratio and distillate composition; namely, and , are calculated for the instantaneous still composition  with the aid of region-dependant algorithms, which incorporate the tangency condition in different ways. Finally, the instantaneous column performance is estimated taking into account the selected operation mode; i.e., constant reflux ratio or constant distillate composition. Applied to the mixture acetone-water, results for complete simulations are presented in terms of both rectification advance and operation time. A brief comparative study on the minimum energy demand required for a given separation as estimated from models with and without tangent pinches is also carried out.