Dynamic Optimization of an Evaporator with a Nonlinear Model Predictive Controller for Application at Modular Micro Rectification

Vapour and liquid phases of a simple batch distillation may be separated theoretically at equilibrium at a certain pressure and temperature state. A small separation effect can be achieved by this, because only one equilibrium stage between liquid and vapour phase is thereby realised. Contacting again vapour and liquid flows leaving one single stage in co-current mode, no further separation effect can be achieved. Under real conditions equilibrium will not be reached, which is then expressed in calculation as tray efficiency. Increased mass and heat transport may be obtained by mixing and separation of flows from single distillation vessels working at different operating points. Such a system of several stages may also be denoted rectification, if the streams leaving the micro devices are connected in counter-current operation mode. Thereby micro devices are as individual modules representing unit operations of such a process. Modular Micro Rectification (MMR) for discontinuous phase contact consists of unit operations heating, cooling, mixing and separating. Heat exchangers, mixers and cyclones for phase separation are serially connected to counter-current rectification system with the highest mass and heat transfer efficiency. Continuous contacting of phases for the purpose of mass and heat transfer at counter-current operation mode with the exception of membrane applications only makes sense up to now for absorption process. Advances were reported by literature for the design of continuous and also discontinuous contacting, counter-current rectification in only one single micro structured apparatus [1,2,3]. Generally continuous phase contacting counter-current micro devices can only be seen as useful without occurrence of mixing effects caused by friction forces on phase interface. However, a plant for Modular Micro Rectification containing several unit operations offers a correspondingly large number of manipulable variables, which have to be coordinated for reasonable handling of the single devices (Fig. 2). Due to the design of micro scaled devices plants form sophisticated systems, while for a fully optimized control still no common satisfying solution exists.