Avaliação do efeito do teor de solvente e da purga na determinação de um procedimento ótimo de partida para um processo de destilação extrativa.

Abstract

From the operational point of view, the start-up operation for a distillation process represents one of the most complex operations in industrial practice. Among the factors that guarantee such complexity are the strongly non-linear behavior associated with the operating restrictions, the high degree of coupling between the process variables and the constant presence of dead time. These characteristics interfere with the time taken for the unit to start operating as desired, resulting in the formation of large quantities of non-specification products, which makes the operation costly. In light of this context, the present work aims to evaluate the effect of the solvent content in the extractive region as an optimization variable for the start-up operation. This thesis proposal arose from the observation of the specialized technical literature, which does not present reports of systematic studies of the solvent content during the extractive distillation units startups. Due to its industrial importance, the dehydration of aqueous ethanol mixtures using ethylene glycol was the chemical system chosen as the case study. Three different solvent levels were found: 30, 50 and 70%; based on the results reported, an increase in the solvent content present in extractive region provides a reduction in the amount of heating utility up to 30,84% for the system, besides this increases provides an reduction in the time undertaken to finish the start-up procedure up to 28,65%. Purge is a preventive operation that generally precedes an initial step and is primarily intended to prevent contamination of products. Despite its importance, this aspect is still one of the most serious and negative aspects of the world. For this reason, this work also analyzed the relationship between purge initiation time and its effect throughout the starting step, in order to contribute to a more realistic dynamic approach. It was verified that the increase in the purge step runtime favors the time undertaken for the extractive column. However, this same increase did not favor the time spent for the recovery column, contributing to a greater amount of time spent overall. The results also showed that an increase in time to execute the purging step provides a reduction in the amount of heating utility up to 1,48% for the system. However, this gain implies operating outside the standard equipment conditions, which may compromise not only equipment but also operator safety. The simulations were developed using Aspen Plus® and Aspen Dynamics®.