Impact of Fluid Flow Patterns on Metastable Zone Width of Borax in Dual Radial Impeller Crystallizer at Different Impeller Spacings
Conducting crystallization in an agitated vessel requires a proper selection of mixing parameters that would result in a production of crystals of specific properties. In dual impeller systems, which are characterized by a more complex hydrodynamics due to the possible fluid flow interactions, revealing a clear link between mixing parameters and crystallization kinetics is still an open issue. The aim of this work is to establish this connection by investigating how fluid flow patterns, generated by two impellers mounted on the same shaft, reflect on metastable zone width of borax decahydrate, one of the most important parameters of the crystallization process. Investigation was carried out in a 15-dm3 bench scale batch cooling crystallizer with an aspect ratio (H/T) equal to 1.3. For this reason, two radial straight blade turbines (4-SBT) were used for agitation. Experiments were conducted at different impeller spacings at the state of complete suspension. During the process of an unseeded batch cooling crystallization, solution temperature and supersaturation were continuously monitored what enabled a determination of the metastable zone width. Hydrodynamic conditions in the vessel achieved at different impeller spacings investigated were analyzed in detail. This was done firstly by measuring the mixing time required to attain the desired level of homogeneity. Secondly, fluid flow patterns generated in a described dual impeller system were both photographed and simulated by VisiMix Turbulent software. Also, a comparison of these two visualization methods was performed. Experimentally obtained results showed that metastable zone width is definitely affected by the hydrodynamics in the crystallizer. This means that this crystallization parameter can be controlled not only by adjusting the saturation temperature or cooling rate, as is usually done, but also by choosing a suitable impeller spacing that will result in a formation of crystals of wanted size distribution.
 W. J. Genck, “Optimizing crystallizer scaleup“, CEP magazine, AIChE, 2003. p. 36-44.
 A. G. Jones, Crystallization Process Systems, London: Butterworth-Heinemann, 2002, pp. 58-141.
 J. W. Mullin, Crystallization, 4th ed., Oxford: Butterworth-Heinemann, 2001, pp. 86-403
 S. S. Kadam, S. A. Kulkarni, R. C. Ribera, H. J . M. Kramer, „A new view on the metastable zone width during cooling crystallization“, Chem. Eng. Sci., 2012. 72: p. 10-19.
 J. Ulrich, C. Striege, “Some Aspects of Importance of Metastable Zone Width and Nucleation in Industrial Crystallizers”, J. Crystal Growth, 2002, 237-239: p. 2130-2135.
 A. Herden, C. Mayer, “About the Metastable Zone Width of Primary and Secondary Nucleation”, Chem. Eng. Technol., 2001, 24 (12): p. 1248-1254.
 N. P. Rajesh, C. K. L. Perumal, P. S. Raghhavan, P. Ramasamy, “Effect of Urea on Metastable Zone Width, Induction Time and Nucleation Parameters of Ammonium Dihydrogen Orthophosphate”, Cryst. Res. Technol., 2001, 36: 55-63.
 N. P. Rajesh et al., “Effect of EDTA on the Metastable Zone Width of ADP”, J. Crystal Growth, 2000, 213 (3-4): p. 389-394.
 C. Frances et al., “Investigations of the Effects of Some Additives on the Crystallization of Tetrahydrate Sodium Perborate”, J. Crystal Growth, 1993, 128 (1-4, Part 2): p. 1268-1272.
 K. Selvaraju, R. Valluvan, S. Kumararman, “Experimental Determination of Metastable Zone Width, Induction Period, Interfacial Energy and Growth of Non-Linear Optical L-Glutamic Acid Hydrochloride Single Crystals”, Mat. Letters 2006, 60 (13-14): p. 1565-1569.
 D. Jayalakshmi, R. Sankar, R. Jayavel, J. Kumar, “Metastable Zone Width, Induction Period and Interfacial Energy of Bis Thiourea Zinc Acetate (BTZA)”, J. Crystal Growth, 2005, 276 (1-2): p. 243-246.
 H. Gürbüz, B. Özdemir, “Experimental Determination of the Metastable Zone Width of Borax Decahydrate by Ultrasonic Velocity Measurement”, J. Crystal Growth, 2003, 252 (1-3): p. 343-349.
 D. O'Grady, M. Barrett, E. Casey, B. Glennon, “The Effect of Mixing on the Metastable Zone Width and Nucleation Kinetics in the Anti-Solvent Crystallization of Benzoic Acid”, Chem. Eng. Res. Des., 2007, 85 (7): p. 945-952.
 A. Chianese et al., “Crystal Growth Kinetics of Pentaerythritol, Chem. Eng. J. Biochem. Eng. J. 58 (3) (1995) 215-221.
 Y. H. Kim et al., “Comparison Study of Mixing Effect on Batch Cooling Crystallization of 3-Nitro-1,2,4-triazol-5-one (NTO) Using Mechanical Stirrer and Ultrasound Irradiation”, Cryst. Res. Technol., 2002, 37 p. 928-944.
 M. Ćosić, A. Kaćunić, N. Kuzmanić, „The Investigation of the Influence of Impeller Blade Inclination on Borax Nucleation and Crystal Growth Kinetics“, Chem. Eng. Comm. 2016. 203 (11): 1497-1506.
 L. Marmo et al., “Influence of mixing on the particle size distribution of an organic precipitate”, J. Crystal Growth, 1996, 166: p. 1027-1034.
 K. Shimizu, H. Nagasawa, K. Takahashi, “Effect of off-Bottom Clearance of a Turbine Type Impeller on Crystal Size Distribution of Aluminum Potassium Sulfate in a Batch Crystallizer”, J. Crystal Growth, 1995, 154: p. 113-117.
 K. Shimizu, T. Nomura, K. Takahashi, “Crystal Size Distribution of Aluminum Potassium Sulfate in a Batch Crystallizer Equipped with Different Types of Impeller”, J. Crystal Growth, 1998, 191 (1-2): p. 178-184.
 K. Shimizu et al., “Effect of Baffle Geometries on Crystal Size Distribution of Aluminum Potassium Sulfate in a Seeded Batch Crystallizer”, J. Crystal Growth, 1999, 197 (4): p. 921-926.
 A Bernardo, M Giulietti, “Modeling of crystal growth and nucleation rates for pentaerythritol batch crystallization”, Chem. Eng. Res. Des., 2010, 88 (10): p. 1356-1364
 M. Akrap, N. Kuzmanić , J. Prlić-Kardum, “Effect of mixing on the crystal size distribution of borax decahydrate in a batch cooling crystallizer”, J. Crystal Growth, 2010, 312 (24): p.3603-3608.
 E. L. Paul, V. A. Atiemo-Obeng and S. Kresta, Handbook of Industrial Mixing, Hoboken, New Jersey: John Wiley and Sons, Inc., 2004, pp. 556-584.
 G. B. Tatterson, Scaleup and Design of Industrial Mixing Processes, McGraw-Hill, New York Inc., 1994, pp. 132-150.
 W. D. Einenkel, A. Mersmann, “The Agitator Speed for Particle Suspension”, Verfahrenstehnik, 1977. 11: p 90-94.
 M. Jahoda et al., “CFD modelling of liquid homogenization in stirred tanks with one and two impellers using large eddy simulation,” Chem. Eng. Res. Des., 2007. 85: p. 616–625.
 A. Kaćunić, M. Ćosić, N. Kuzmanić, “Impact of mixing parameters on homogenization of borax solution and nucleation rate in dual radial impeller crystallizer“, Int. J. Chem. Molec. Nucl. Mater. Metal. Eng., 2016. 10: p.75-80.
 S. Ibrahim, A. W. Nienow, “Power curves and flow patterns for a range of impellers in Newtonian fluids: 40 < Re < 5×105”, Trans. IChemE, 1995. 73: p.485-491.
 R. Kuboi, A. W. Nienow, “The power drawn by dual impeller systems under gassed and ungassed conditions”, in: Proc. 4th European Conference on Mixing, Cranfield, Bedford, England, 1982 , pp. 247-261.
 Z. X. Weng, “The effect of the distance between multiple impellers in the turbulent tank”, Chem. Eng. J. 1983. 6: p. 1–6.
 V. Mishra, J. Joshi, “Flow generated by a disc turbine. IV: Multiple impellers”, Chem. Eng. Res. Des., 1994. 72: p. 657-668.
 A. Kacunic, M. Akrap, N. Kuzmanic, “Effect of impeller type and position in a batch cooling crystalizer on the growth of borax decahydrate crystals“, Chem. Eng. Res. Des., 2013. 91: p. 274-285.
 A. Myerson, Handbook of Industrial Crystallization, Boston: Butterworth-Heinemann, 2002, pp. 1-218.
 G. Yang et al., “A Model for Prediction of Supersaturation Level in Batch Cooling Crystallization”, J. Chem. Eng. Japan, 2006. 39 (4): p. 426 - 436.
 A. Chianese, A. Contaldi, B. Mazzarotta, “Primary Nucleation of Sodium Perborate in Aqueous Solutions”, J. Crystal Growth, 1986. 78: p. 279-290.