Analysis of an Oscillating Two-Stage Evaporator System through Modelling and Simulation: an Industrial Case Study

With increasing demands on the industry for resource efficiency, processes are often built or retrofitted withrecycle streams in order to decrease energy and raw material demands. However, this also increases thecomplexity of the process as a whole and may bring unexpected effects. In this contribution, such a case,consisting of a two-stage evaporator system, fed with the product stream of an upstream batch system and acontinuous recycling stream from downstream separation processes, was analyzed. This evaporator systemwas subject to potentially performance-limiting oscillating disturbances. The purpose of this study was to,through modelling and simulation, expand the knowledge of the system by analyzing the system dynamics,and to discover any co-oscillations and their extent in the process, as well as their effect on processparameters such as product purity and the energy usage in terms of steam consumption. The investigationwas performed by modelling using Aspen Plus Dynamics. Simulation, data-extraction, and analysis wasperformed via a COM enabled Python interface. The results of the study highlight the full-system propagationof oscillations along with co-oscillation of selected key parameters, and support the conclusion that there ispotential for cost-reductions by decreasing steam consumption by 1.1 %, without any investments.