Naslov
Influence of impeller speed on borax crystallization in dual-impeller batch cooling crystallizer

Autori
Kaćunić, Antonija ; Ćosić, Marija ; Kuzmanić, Nenad

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

Izvornik
13th Mediterranean Congress of Chemical Engineering - Book of Abstracts / - Barcelona, 2014, 61-61

Skup
13th Mediterranean Congress of Chemical Engineering

Mjesto i datum
Barcelona, Španjolska, 30.09.2014. - 03.10.2014

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
dual impeller system ; impeller speed ; borax ; crystallization

Sažetak
This work gives an insight into the impact of impeller speed in a dual-impeller crystallizer on the process of batch cooling crystallization of disodium tetraborate decahydrate (borax). Experiments were conducted in a 15 L baffled batch cooling reactor with specific geometrical characteristics at linear cooling rate of 6°C/h. Mother liquor mixing was performed using the straight blade turbine (4-SBT) that created a radial flow pattern in the system. Mentioned specific geometrical characteristics primarily relate to the liquid level to vessel diameter ratio (H/dT). Since that ratio was 1.3, an installation of a second impeller was required. The ratio of impeller diameter to vessel diameter, D/dT was 0.33 while the ratio of impeller off-bottom clearance and impeller spacing to the impeller diameter ratios, c/D and s/D respectively, equaled 1. In order to reveal the degree of influence that a dual- impeller system has on the process of crystallization of borax, the same had to be compared to the single-impeller system setup. Considering the fact that the observed system is a solid-liquid suspension, initial experiments were carried out at the recommended impeller speed that ensured the state of a complete suspension (NJS). Further runs included entering the intermedial suspension state since the impeller speed, N to NJS ratio was varied from 1 to 2. This kind of an experimental setup enabled a detailed analysis of the impact of different impeller speed on nucleation and crystal growth kinetic parameters, growth rate, crystal size distribution (CSD) and crystal shape as well. During the process, mother liquor concentration was monitored in-line by the use of a Na ion- selective electrode. Linear crystal growth was determined by the means of optical microscopy where the samples were analyzed using Motic Images Plus 2.0 software. At the end of the process, crystal product was dried and then subjected to sieving to determine the crystal size distribution. To calculate the power consumption at different impeller speeds, data acquisition software was used to monitor and analyze torque values. Results showed that an installation of a second impeller in a system with geometrical characteristics described earlier, leads to a decrease in NJS but with no significant change in power consumption. The effect that an increase in impeller speed in a dual-impeller system has on nucleation kinetic parameters, crystal growth kinetic parameters, growth rate and crystal size distribution is evident. This influence is especially pronounced when it comes to crystal shape of the final product at N/NJS=2 where more than 85% of the final crystal product is regularly shaped. An increase in impeller speed in a dual-impeller system shows an expected increase in power consumption but with no fluctuations in its value over time. Nevertheless, it should be emphasized that these experiments were carried out in laboratory scale and that formation of a new (solid) phase in the system would most likely have to have an impact on the change of power consumption if the same would be implemented in a much larger scale.

Izvorni jezik
Engleski

Znanstvena područja
Kemijsko inženjerstvo

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