Überwachung und Steuerung der kontinuierlichen mehrstufigen Wirbelschichtsprühgranulation: Echtzeitanalyse und Prozessanpassung durch Mischungsbeeinflussung
Zusammenfassung der Projektergebnisse
The industrial-scale fluid spray granulation plays a key role in many industries, such as petrochemical, pharmaceutical, food, and fertilizer industries, in order to scale up particle granulation of fine powders or special formulations. The common use of spray granulation is in order to improve the flowability of the powder in order to improve the dosage, reduce transport problems, alleviate explosion hazards for very fine powders, and overall to make the material in question of better quality and easier to manage on an industrial scale. The spray granulation process requires the addition of a liquid phase through, usually, twofluid nozzles that atomize the binding solution and enable particles to collide with each other and grow as the liquid is dried. In order to enable this binding process, avoid particle overgrowth and increase general particle homogeneity, the fluidization of the bed is of paramount importance. In essence, a carrying fluid, in this case hot air, inserted below the load of particles to be processed inducing a drag force onto them, which is compensated by the gravity force, induces a fluidization state in which particle sets behave more like a liquid than a bulk solid. In this state particles collide with each other, they mix homogeneously and reduce risks or local hot spots or product heterogeneity. However, these processes suffer from problems such as, potential defluidization, accumulation of overgrown particle and final process shut down. In order to avoid such issues, the particle growth needs to be monitored and process parameters such as, fluidization velocity, spray pressure or air temperature are modified in order to react to the changing conditions. However, once the particles have already overgrown, few approaches remain other than shutting down and cleaning the particle inventory, leading to downtime and subsequent cost. To that end this project attempts to create a system that allows for the heterogeneous fluidization of the bed in order to remove overgrown particles, create localize segregation, while still allowing for the homogeneous aeration mode during normal operation. A brand-new steel grid system was built under the distributor plate in order to allow for this actuation mode, which was after the appropriate, calibration and function check, used to operate in an industrial fluidized spray granulator and the hypothesized particle size segregation and particle movement was checked by ex-situ particle size distribution analysis and particle tracking velocimetry. This procedure confirmed a couple of assumptions, one that the segregation takes place in some configuration, two that the particle clean up can take place by the use of a spouted configuration, and three that the top spray configuration can still be carried out without much obstruction of the new system. All in all, the system enables another degree of freedom in the fluidized spray granulation process with a very modest investment and almost no obstruction of the top spray granulation, while the bottom spray granulation would require the grids to be slightly modified to accommodate for the pass-through nozzles but for the sake of simplicity that has not been implemented in this funding period.
Projektbezogene Publikationen (Auswahl)
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Control of segregation by non-uniform aeration in a fluidized bed spray granulator. Powder Technology, 435, 119348.
Atxutegi, A.; Atzori, M.; Bettien, J.; Lichtenegger, T.; Puttinger, S.; Pirker, S. & Heinrich, S.
