2 research outputs found
Batch Crystallizer Scale-up
U svrhu pronalaženja odgovarajuÄeg pravila uveÄanja, provedena su mjerenja u tri geometrijski sliÄna kristalizatora Rushtonovih dimenzija razliÄitih veliÄina, u laboratorijskom mjerilu. Za mijeÅ”anje je upotrijebljeno mijeÅ”alo s Äetiri lopatice nagnute pod kutem od 45Ā°. Mjerenja su provedena pri razliÄitim hidrodinamiÄkim uvjetima, odnosno razliÄitim brzinama vrtnje mijeÅ”ala. Za kriterij usporedbe primijenjene su granulometrijske karakteristike (oblik i raspodjela veliÄina) dobivenih kristala. Provedena je Å”aržna kristalizacija hlaÄenjem vodene otopine kalijeva klorida. Kalijev klorid je odabran radi izuzetne osjetljivosti na radne uvjete. Naime i oblik i raspodjela veliÄina kristala jako se mijenjaju s promjenom radnih uvjeta. PoboljÅ”anjem hidrodinamiÄkih uvjeta u kristalizatoru dobivaju se kristali pravilnijeg oblika. Ispitana je primjenljivost razliÄitih pravila uveÄanja, koja se primjenjuju kod ureÄaja za mijeÅ”anje suspenzija. S obzirom da hidrodinamiÄki uvjeti u kristalizatoru u velikoj mjeri utjeÄu na kvalitetu dobivenog produkta (oblik, veliÄina i granulometrijski sastav kristala), uz geometrijsku sliÄnost nije moguÄe zadovoljiti niti jedan istraživan kriterij uveÄanja. Na temelju metodologije koja se primjenjuje za uveÄanje kada se mjerenja mogu provesti u tri ili viÅ”e ureÄaja, odreÄen je kriterij uveÄanja Å”aržnog kristalizatora za kristalizaciju kalijeva klorida hlaÄenjem iz vodene otopine.In order to define an appropriate scale-up criterion for a batch crystallizer batch cooling crystallization of potassium chloride from the aqueous solution has been performed. The measurements were undertaken on the laboratory scale in three geometrically similar pieces of equipment (Table 1) under mixing intervals from 300 to 600 min ā1 . A stirrer was supplied with pitched (at 45Ā°) 4- blade propeller. Granulometric properties (shape and size distribution) of the obtained crystals were used as a comparison criterion. Hydrodynamic conditions in the crystallizer and size of the equipment had major influence on the properties of the crystals. Under higher mixing intensity and with larger equipment the crystals assumed more regular shape (Fig. 3.), and their size distribution showed finer fractions (Fig. 2, Fig. 4.). Actually, these conditions reduced the amount of agglomerates in the finished product. In addition, better hydrodynamic conditions for heat and mass transfer were achieved, whereas the secondary nucleation (contact) was minor. The comparison between the obtained crystal size distributions in all three pieces of laboratory equipment showed that the mixing rate of n = 500 min ā1 yielded satisfactory results (Fig. 4 b.). They were further used to define the scale-up criterion for the batch crystallizer. Applicability of different scale-up criteria to the suspension stirrers was tested. Compliance with the geometric similarity and hydrodynamic conditions did not allow for compliance with the conventional scale-up criteria (Fr = const, Re = const). Based on the scale-up methodology, when the measurements can be undertaken in three or more pieces of equipment, the scale-up criterion, for the batch crystallizer for cooling crystallization of potassium chloride from the aqueous solution, is defined (Fig. 5.). The methodology proposed for the studied crystallizer gives a relatively low mixing intensity (237 min ā1), which corresponds to the solution homogeneity 1 (Table 2.). Given that crystallization required suspension homogeneity between 6 and 9 (Chemineer ChemScale),8 implying that the suspension homogeneity was 95ā98 % of the liquid height, the mixing intensity for these conditions were determined as well. The obtained values were within the range of the used mixing intensity
Batch Crystallizer Scale-up
U svrhu pronalaženja odgovarajuÄeg pravila uveÄanja, provedena su mjerenja u tri geometrijski sliÄna kristalizatora Rushtonovih dimenzija razliÄitih veliÄina, u laboratorijskom mjerilu. Za mijeÅ”anje je upotrijebljeno mijeÅ”alo s Äetiri lopatice nagnute pod kutem od 45Ā°. Mjerenja su provedena pri razliÄitim hidrodinamiÄkim uvjetima, odnosno razliÄitim brzinama vrtnje mijeÅ”ala. Za kriterij usporedbe primijenjene su granulometrijske karakteristike (oblik i raspodjela veliÄina) dobivenih kristala. Provedena je Å”aržna kristalizacija hlaÄenjem vodene otopine kalijeva klorida. Kalijev klorid je odabran radi izuzetne osjetljivosti na radne uvjete. Naime i oblik i raspodjela veliÄina kristala jako se mijenjaju s promjenom radnih uvjeta. PoboljÅ”anjem hidrodinamiÄkih uvjeta u kristalizatoru dobivaju se kristali pravilnijeg oblika. Ispitana je primjenljivost razliÄitih pravila uveÄanja, koja se primjenjuju kod ureÄaja za mijeÅ”anje suspenzija. S obzirom da hidrodinamiÄki uvjeti u kristalizatoru u velikoj mjeri utjeÄu na kvalitetu dobivenog produkta (oblik, veliÄina i granulometrijski sastav kristala), uz geometrijsku sliÄnost nije moguÄe zadovoljiti niti jedan istraživan kriterij uveÄanja. Na temelju metodologije koja se primjenjuje za uveÄanje kada se mjerenja mogu provesti u tri ili viÅ”e ureÄaja, odreÄen je kriterij uveÄanja Å”aržnog kristalizatora za kristalizaciju kalijeva klorida hlaÄenjem iz vodene otopine.In order to define an appropriate scale-up criterion for a batch crystallizer batch cooling crystallization of potassium chloride from the aqueous solution has been performed. The measurements were undertaken on the laboratory scale in three geometrically similar pieces of equipment (Table 1) under mixing intervals from 300 to 600 min ā1 . A stirrer was supplied with pitched (at 45Ā°) 4- blade propeller. Granulometric properties (shape and size distribution) of the obtained crystals were used as a comparison criterion. Hydrodynamic conditions in the crystallizer and size of the equipment had major influence on the properties of the crystals. Under higher mixing intensity and with larger equipment the crystals assumed more regular shape (Fig. 3.), and their size distribution showed finer fractions (Fig. 2, Fig. 4.). Actually, these conditions reduced the amount of agglomerates in the finished product. In addition, better hydrodynamic conditions for heat and mass transfer were achieved, whereas the secondary nucleation (contact) was minor. The comparison between the obtained crystal size distributions in all three pieces of laboratory equipment showed that the mixing rate of n = 500 min ā1 yielded satisfactory results (Fig. 4 b.). They were further used to define the scale-up criterion for the batch crystallizer. Applicability of different scale-up criteria to the suspension stirrers was tested. Compliance with the geometric similarity and hydrodynamic conditions did not allow for compliance with the conventional scale-up criteria (Fr = const, Re = const). Based on the scale-up methodology, when the measurements can be undertaken in three or more pieces of equipment, the scale-up criterion, for the batch crystallizer for cooling crystallization of potassium chloride from the aqueous solution, is defined (Fig. 5.). The methodology proposed for the studied crystallizer gives a relatively low mixing intensity (237 min ā1), which corresponds to the solution homogeneity 1 (Table 2.). Given that crystallization required suspension homogeneity between 6 and 9 (Chemineer ChemScale),8 implying that the suspension homogeneity was 95ā98 % of the liquid height, the mixing intensity for these conditions were determined as well. The obtained values were within the range of the used mixing intensity