Influence of fluid flow pattern in dual sbt batch crystallizer on metastabile zone width of borax : diploma thesis

Cilj ovog rada je bio ispitati utjecaj tokova u šaržnom kristalizatoru s dvama turbinskim SBT miješalima na širinu metastabilne zone dinatrijevog tetraborat dekahidrata (boraksa). Proces se odvijao u kristalizatoru volumena 15 dm 3 u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog SBT miješala u sustav. Detaljno je analiziran utjecaj pozicije dvaju SBT miješala na promjenu prezasićenosti i širinu metastabilne zone. Da bi se dobio potpuniji uvid u hidrodinamička zbivanja u ispitivanom sustavu, pri svim uvjetima miješanja je određeno i vrijeme homogenizacije te je vizualizirana struktura toka kapljevine fotografiranjem kao i simulacijom istih. Simulacija je izvršena uporabom računalnog programa VisiMix Turbulent. Korištene metoda vizualizacije su detaljno analizirane i uspoređivane. Ispitivanjima je utvrđeno da širina metastabilne zone boraksa značajno ovisi o hidrodinamičkim uvijetima u kristalizatoru. Vizualizaciju tokova neophodno je provoditi s dvije primjenjene tehnike. Naime, pri određenim „rubnim“ pozicijama miješala, računalni program VisiMix Turbulent ne ukazuje na deformacije tokova koje se pojavljuju u određenim djelovima kristalizatora, a koje definitivno utječu na širinu metastabilne zone boraksa.The aim of this research was to examine the influence of fluid flow pattern in a SBT - dual impeller batch on the metastable zone width of disodium tetraborate decahydrate (borax). The process was carried out in a 15 dm 3 volume crystallizer, in which the ratio of tank diameter to liquid height ratio was equal to 1.3. This aspect ratio required the use of a second impeller in the system which was mounted on the same shaft. An impact of SBT – dual impeller configuration on supersaturation change during process time and metastable zone width was thoroughly analyzed. In order to gain a more complete insight into the hydrodynamics of the crystallizer, mixing time was determined and fluid flow pattern was visualized by photographing and by simulating. Simulation was performed using the VisiMix Turbulent computer program. Also, used visualization methods of fluid flow pattern were specifically analyzed and compared. Experimental results have shown that the metastable zone width of borax depends significantly on hydrodynamic conditions in the crystallizer. Fluid flow pattern visualization is necessary to implement two aplied techniques. Specifically, at a certain "border" positions in dual impeller system, VisiMix Turbulent computer program did not point to deformations in the flow occurred in certain parts of the crystallizer, which definitely affect the metastable zone width of borax