Dynamics and control of falling film evaporators with mechanical vapour recompression

This paper develops and analyses a model of a falling film evaporator with mechanical vapour recompression for the purpose of examining the coupling a nd functional controllability of the three core control loops for effect te mperature, product dry mass fraction and product flowrate. The Relative Gai n Array is used to assess coupling, and the functional controllability anal ysis uses the methodology of Skogestad and Postlethwaite(1). This determine s if adequate levels of disturbance rejection can be achieved with allowabl e levels of manipulation. The aim is to understand the fundamental properties of the process which li mit the ability of the control system to reject disturbances. A first princ iples model of appropriate complexity which captures the essential mechanis ms is developed and used. Initially a single pass evaporator is studied, th e applicability of the results to multi pass systems is considered.