Luís Gonzaga Sales Vasconcelos

Optimization of the Design and Operation of Extractive Distillation Processes

The achievement of the optimal operating point of extractive distillation systems involves determining the values of the process variables, such as the solvent flowrate, the reflux ratio of the extractive, and recovery columns. From the point of view of design, the optimum involves defining the number of stages of extractive and recovery columns, as well as the feed stage positions of these columns. The above-mentioned columns are coupled through a recycle stream, which makes obtaining the optimal operating and design points a more complex task. This study arose from a new procedure for the analysis of extractive distillation columns, in which the solvent mole fraction in the solvent feed stage is the primary variable to be analyzed. The procedure allows for determining the values of the process and design variables that provide the global minimum for the total annual cost and the specific energy consumption of the extractive distillation processes (extractive and recovery columns). Furthermore, it is possible to determine the minimum solvent flowrate and the minimum reflux ratio for separation. Obtaining anhydrous ethanol using ethylene glycol as solvent is the case study of this work.

Effect of Solvent Content on the Separation and the Energy Consumption of Extractive Distillation Columns

This article sets out to evaluate the effect of solvent content in the extractive section on the separation efficiency and energy consumption of extractive distillation columns. Contrary to the classical approach, the proposed approach enables a simultaneous evaluation of the effect of the major decision variables (reflux ratio, solvent flow rate, and the number of stages of the extractive section [NSE]). The procedure allows calculating the minimum solvent flow rate for the separation and the minimum specific energy consumption. The results show that the minimum specific energy consumption is obtained for the minimum reflux ratio and not for the minimum solvent flow rate. Moreover, the results show that it is not always the case that a larger NSE results in lower energy consumption. Due to its industrial importance, the dehydration of aqueous mixtures of ethanol using ethylene glycol as solvent has been chosen as a case study.

Economic evaluation of energy saving alternatives in extractive distillation process

Abstract Until now, there has not been consensus about the superiority of thermally coupled sequence over the conventional sequence in the extractive distillation process. In this sense, the main goal of this paper is to analyze three approaches for saving energy in the extractive distillation process: optimization, thermal integration and thermal coupling. Three azeotropic mixtures were investigated: ethanol and water (M1); tetrahydrofuran and water (M2); and acetone and methanol (M3). The solvents were ethylene glycol for M1 and M2, and water for M3. The results are shown in terms of the total annual cost (TAC) and specific energy consumption (SEC), and revealed that a thermally coupled extractive distillation sequence with a side rectifier did not always present the best results. Taking the case studies from literature as a starting point (without thermal integration), the optimization procedure used in this work found that TACs are always lower. The inclusion of thermal integration in configurations led to reducing TAC for all mixtures under investigation when compared to the sequences without this integration. When comparing two modifications in the layout of extractive distillation, it can be seen that it is more advantageous to use the preheating of the azeotropic feed with the recycle stream from the recovery column of the conventional sequence than using a thermally coupled sequence.

Optimal Operation of an Industrial PVC Dryer

This article describes the design of a control structure architecture for an industrial polyvinyl chloride (PVC) dryer, currently operating at Braskem Company (Marechal Deodoro, Alagoas, Brazil). The underlying motivation is to search for a control configuration that leads to optimal economic operation, while promptly rejecting disturbances at lower layers in the control hierarchy. We start by optimizing a nonlinear model of the process with respect to reducing energy consumption as a criterion of optimization for different disturbance scenarios. The results show that it is optimal to control the temperature level of the utilities serving the dryer and the outlet PVC moisture contents at their respective upper bounds. In addition, the flow of air to the dryer should be fixed at its optimum nominal setpoint despite disturbances. Application of this strategy results in a reduction of about 16% in energy consumption with respect to the current dryer operation policy and a 22% increase in throughput under nominal operation. In addition, almost perfect indirect control of the outlet PVC moisture was achieved by tightly controlling a temperature difference in the dryer. The proposed decentralized control configuration gives good dynamic performance for the outlet PVC moisture content with maximum settling time of about 1.8 h for the more difficult disturbance of increasing the inlet slurry moisture content by 40% and magnitude of overshoot of ca. 5% w.r.t. the optimum setpoint for an increase of 20% in PVC feed flow rate to the dryer.

Exergetic and economic analysis of an industrial distillation column

In this work, applications of exergy and economic concepts to compression, heat exchange, and separation processes were used for calculation of the irreversibility rate, thermodynamic efficiency, and internal rate of return (IRR) of the profitability. A case study based on a real process, the purification of 1,2-dichloroethane (DCE) in a high-purity distillation column, is presented. This column has the highest steam flow rate in any vinyl chloride monomer (VCM) plant. A configuration using a vapor compression heat pump is proposed for improvement of the energy efficiency without having to make important process modifications. Existing and proposed configurations were implemented using the Aspen Plus™ commercial simulator; the results of the existing configuration were validated with data extracted from the plant. The objective of this work was to compare the existing configuration with the proposed one, using a thermodynamic and an economic approach.

IDENTIFICAÇÃO DE SISTEMA E CONTROLE EM UMA UNIDADE DE COMPRESSÃO DE CLORO

RESUMO – Em todo o mundo, indústrias químicas e petroquímicas têm se envolvido em acidentes cujos reflexos econômicos, humanos e ambientais muitas vezes ultrapassam os limites de suas instalações, devido à presença de impurezas. Na produção de Cl2 (cloro), à presença da amônia (NH3) no sal, dá origem a Tricloroamina (NCl3), que é um composto extremamente instável e explosivo em determinadas condições de operação. Neste trabalho foi realizada a Identificação do Sistema na planta de Cl2, assim como, proposta uma estratégia de controle, no Simulink/Matlab. O fluxograma do processo utilizado foi desenvolvido no Aspen Dynamics. Sinais de excitação do tipo degrau e PRBS foram aplicados na vazão de Cl2 gás, na vazão de Cl2 líquido na entrada do pré resfriador, além da Carga térmica do Reator. Os testes em malha aberta foram realizados com o intuito de entender e tirar conclusões sobre o comportamento transiente das variáveis em estudo. Os modelos do tipo Função de Transferência, ARX e Espaço de Estados, foram os que melhor se ajustaram ao comportamento dos dados, em estado transiente, do sistema. Já a malha de controle proposta ao final desse estudo, traz uma justificativa para a não implementação de controle à temperatura do 1o estágio do compressor, visto que a mesma ao invés de afetar no controle Temperatura do Reator, provoca uma elevada saturação na mesma.