Otimização e controle integrado de variáveis-chave: unidade de destilação de peróxido de hidrogênio

Abstract

The steam consumption by hydrogen peroxide (H2O2) distillation columns is quite representative. Aiming the energetic annual cost reduction, it is proposed to simulate an integrated control system that seeks the unity continuous operation under desired specifications and based on minimum required steam flowrate. For the development of this control strategy, it is considered, by simplification, as key-process variables: H2O2 feed flow, reflux flow, steam flow, H2O2 column top overheads and H2O2 final product concentration. First of all, both the steam flow and H2O2 column top overheads modeling based on influence of other key-process variables are developed. Assuming the final product concentration is constant and equal to 70,3% by weight and the maximum allowable H2O2 column top overheads is 1000 ppm, the maximum savings related to the unity is associated to the operation that guarantees these specificities with minimum reflux flowrate and consequently with minimum possible steam flowrate. In this context, a methodology with statistical basis is applied to predict, without many field tests, a well adjusted predictive model for reflux and steam flow. Precisely these models, when applied, and fed by H2O2 feed flow, free control variable (choosed by Production sector), and by maximum allowable H2O2 column top overheads set-point, will first ensure the reflux flow minimization and consequently the steam flow minimization. In addition to predictive models destined to process optimization, open-loop transfer functions of both reflux and steam flow are also sought. Finally, the PID adjustment each loop is performed so that they are integrated. The reflux and steam open-loops can be classified as integrated, since the process value, optimized reflux flowrate, will be fed into the predictive model contained in steam controller to obtain the new minimum steam flowrate to process. Besides resulting financial gains, in the case of implementation, the project contemplates an innovative alternative for process control that can be diffused to other process areas.