Jörg Hackenberg, Achim Helbig, Wolfgang Marquardt:
Modeling, dynamics and control of horizontal tube falling film multi-effect desalination plants
In: Encyclopedia of Desalination and Water Resources (DESWARE), EOLSS Publishers Co. Ltd., Oxford, UK, EOLSS Publishers Co. Ltd., Oxford, UK, 2000
This article summarizes the state of the art in dynamic modeling and control of horizontal tube falling film multi-effect (ME) distillers with a steam jet ejector for thermal vapor compression (TVC) using a case study approach. A dynamic first principle model has been constructed for a four-effect plant. Selected modeling issues such as heat transfer coefficient, carbon dioxide and ejector modeling are addressed. The dynamics of the plant have been studied with nonlinear simulation and by a linear controllability analysis. The analysis showed that there are no significant limitations to the achievable control performance inherent in the plant design. Based on the linear analysis results a decentralized control structure has been suggested. The resulting structure corresponds to the structure commonly implemented on actual ME plants. PI-type controllers were used to implement the control structure. It has been shown in dynamic nonlinear simulations that these controllers give satisfying control performance provided that they are properly tuned. Finally, model predictive control (MPC) technology was applied to the ME plant. MPC did not achieve better control performance than the decentralized control structure employing PI-type controllers in base control cases. However it could be shown that the application of MPC to advanced control objectives like control of a performance index is promising.