Plantwide control systems design and evaluation applied to biodiesel production

Abstract

Chemical processes have complex dynamic behaviors due to the presence of recycle streams, heat integration and several unit operations being interconnected, leading to interaction problems among variables and difficulties in completing an effective process control. Plantwide control methodologies aim to establish control systems for entire chemical plants; however, it is possible to obtain different control solutions. This work proposes that the evaluation of different plantwide control structures for a specific process could be carried out using key performance indicators (KPIs) to determine which control method best meets the industry strategic goals. In order to evaluate the proposed approach a typical biodiesel process model was implemented in Aspen Plus Dynamics; the selected KPIs were the dynamic disturbance sensitivity and an economic indicator that represents the variation of the ratio between the product’s selling price and the raw material cost over time. It was observed that both KPIs allowed a view of the plantwide control system performance and aided in choosing a set of designed controllers. However, the economic indicator enables one to choose a set of designed controllers that reduce the variability of the economic indicator by around 74% while providing a slight increase in the indicator mean value.