Naslov
The influence of impeller blade angle on crystallization kinetic of borax decahydrate

Autori
Akrap, Marija ; Kuzmanić, Nenad ; Prlić Kardum, Jasna

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
8th European Congress of Chemical Engineering / 1st European Congress of Applied Biotechnology (ECCE/ECAB 2011)

Mjesto i datum
Berlin, Njemačka, 25.09.2011. - 29.09.2011

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
borax decahydrate; batch cooling crystallization; impeller blade angle; nucleation mechanism; kinetic parameters of crystal growth rate

Sažetak
The effect of impeller blade angle on the nucleation kinetics, crystal growth rate, crystal size distribution and crystal shape of borax decahydrate has been investigated. The importance of blade angle was studied in a laboratory scale unseeded batch cooling crystallizer equipped with four-bladed turbine. The blade angle to the horizontal axis was varied from 30° to 90°. Experiments were performed at constant impeller diameter, off-bottom clearance and impeller speed of 350 rpm which ensured the state of complete suspension in the crystallizer. Obtained results show that the maximum value of the supersaturation, cmax, decreases with increasing impeller blade angle. The nucleation behaviour was estimated according to Mersmann's criteria. In all examined systems the nucleation takes place by heterogeneous nucleation mechanism. Impeller blade angle has also affected the crystal growth. Numerical values of order of crystal growth indicate that the growth of crystals was controlled by combination of diffusion and surface-integration growth mechanism regardless of impeller blade angle. The differences in values of second growth kinetic parameter, that is crystal growth rate constant, point to the different fluid dynamic conditions in the crystallizers caused by impeller blade angle. Namely, the increment of impeller blade angle significantly changes flow pattern in the crystallizer from axial to radial, reflecting on the crystal size distribution and shape of crystal product as well. In this work torque measurements were also performed to evident power consumption in systems with diferrent impeller blade angle. Since the crystallization is process in which a new, solid phase forms from supersaturated solution, a data acquisition software package was used to evident the possible changes of power consumption during the process. It was found that the power consumption per unit mass of suspension increased as blade angle increase. In examined systems this parameter is nearly constant over process time, so they do not change over the process time regardless of the fact that during the process the new solid phase forms.

Izvorni jezik
Engleski

Znanstvena područja
Kemijsko inženjerstvo

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