The influence of mixing on crystallisation is often ignored despite the fact that it affects almo... more The influence of mixing on crystallisation is often ignored despite the fact that it affects almost every aspect of the process what is especially pronounced in multiple impeller systems where flow complexity is increased. The predominant motivation for this work was to investigate the effect of mixing on nucleation kinetics of borax in the process of batch cooling crystallisation. Crystallisation was conducted in 15 dm3 crystalliser with an aspect ratio (H/dT) equal to 1.3. Such aspect ratio required an installation of a second impeller on the same shaft. Mixing was performed by using two down pumping pitched blade turbines (PBT impellers). Mother liquor was saturated at 30 °C and it was cooled down at 6°C/h. The impact of several mixing parameters, such as impeller speed, size and position, was examined. A key parameter for evaluating the blending effectiveness of stirred tanks – mixing time, was determined by potentiometric method whiles the nucleation mechanism and rate was determined using the Mersmann's nucleation criterion. Obtained results indicate that investigated mixing parameters affect the values of mixing time and consequently the nucleation kinetics. Considering the stated, by choosing proper mixing parameters, it is possible to influence the characteristic of the final product of crystallisation.
Main focus of this work was to investigate the influence of hydrodynamic conditions on crystalliz... more Main focus of this work was to investigate the influence of hydrodynamic conditions on crystallization kinetics and properties of borax crystals obtained in a 15 dm 3 dual impeller batch cooling crystallizer. The two impellers used, pitched and straight blade turbine, were mounted on the same shaft. Hydrodynamics was analyzed through the values of mixing time and specific fluid flow patterns generated. Results indicate that wider metastable zones were generally observed at impeller positions characterized by higher mixing times. In those cases, growth rate constants were lower what resulted in a formation of smaller but more regularly shaped crystals. These findings imply that dual impeller position should be taken into account in order to produce crystals of desired characteristics.
Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim mije... more Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim miješalima na kinetiku kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) tijekom njegove šaržne kristalizacije kontroliranim hlađenjem. Proces je provođen u kristalizatoru volumena 15 dm3, u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog miješala u sustav. Miješanje se provodilo korištenjem triju različitih konfiguracija dvaju miješala: PBT-PBT, SBT-SBT te PBT-SBT. Za svaku primjenjenu konfiguraciju miješala detaljno je ispitan utjecaj brzine vrtnje, promjera miješala, udaljenosti donjeg miješala od dna te međusobne udaljenosti dvaju miješala na mehanizam i brzinu nukleacije, kinetiku rasta kristala boraksa te granulometrijske karakteristike finalnog produkta. U radu je također analiziran i utjecaj brzine hlađenja matične otopine na kinetiku ispitivanog procesa. Da bi se dobio potpuniji uvid u hidrodinamička zb...
Conducting crystallization in an agitated vessel requires a proper selection of mixing parameters... more 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-dm<sup>3</sup> bench scale batch cooling crystallizer with an aspect ratio (<em>H</em>/<em>T</em>) equal to 1.3. For this reason, two radial straight blade turbines (4-SBT) were used for agitation. Experiments were conducted at different impeller spacin...
Open loop dynamic testing and closed loop automatic control have been devised, implemented and qu... more Open loop dynamic testing and closed loop automatic control have been devised, implemented and quantitatively evaluated on a portable laboratory workstation, with the aim of serving Chemical and Process Engineering students with practical training. A basic case study was conceived on level control. Classical evaluations, both qualitative and quantitative, were carried out on the dynamic response experimentally obtained on the workstation, either at open or closed loop, including the quality of the feedback action by means of the controller performance indexes (e.g., IAE; ISE; ITAE; ITSE).Although conceptually simple, the experimental activities turned out a rather demanding task in terms of time, data elaboration and interpretation work, but they provided a continuous beneficial interaction between the lecturer and the student. The developed technique, the tests with the workstation and the encouraging results obtained so far promise to be a very useful educational tool for undergra...
The aim of this work was to determine the influence of cooling rate on the nucleation and crystal... more The aim of this work was to determine the influence of cooling rate on the nucleation and crystal growth of borax decahydrate. All experiments were carried out in baffled stirred crystallizer with the volume of 2.14 dm3. Mother liquor saturated at 30 °C was cooled down at 3 different cooling rates in the range from the 4 to 9 °C/h. In order to analyze and compare the influence of fluid flow pattern in the crystallizer on product properties, examinations were performed using two different impeller types; radial straight blade turbine (SBT) and axial pitched blade turbine (PBT). Mixing with both of impellers was carried out at constant impeller speed of 300 rpm. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over process time were determined by optical microscope and image analysis software. The nucleation and crystal growth behaviors for borax–water system in a batch cooling crystallizer were estimated according to Mersm...
Ovaj rad prilog je sustavnom inženjerskom istraživanju u marikulturi s teorijskog motrista. Temat... more Ovaj rad prilog je sustavnom inženjerskom istraživanju u marikulturi s teorijskog motrista. Tematikom pripada podrucju matematickog modeliranja b
Cilj rada je bio ispitati utjecaj hidrodinamickih uvjeta u kristalizatoru s dvama turbinskim mije... more Cilj rada je bio ispitati utjecaj hidrodinamickih uvjeta u kristalizatoru s dvama turbinskim mijesalima na kinetiku kristalizacije dinatrijevog tetr
Mnoge operacije u kemijskoj industriji u velikoj mjeri ovise o uspjesno provedenom mijesanju. Kol... more Mnoge operacije u kemijskoj industriji u velikoj mjeri ovise o uspjesno provedenom mijesanju. Koliko ce ono biti uspjesno moguce je procijeniti kroz nekoliko parametara, pa tako i kroz poznavanje vrijednosti snage mijesanja. Snaga mijesanja predstavlja energiju preko mijesala dovedenu u sustav. Njezina vrijednost, između ostalog, utjece i na velicine važne pri provedbi procesa kristalizacije kao sto su stupanj izmjesanosti te koeficijent prijenosa tvari. U ovom istraživanju, saržna kristalizacija boraksa je provedena u sustavu volumena 15 dm3 pri cemu je omjer visine stupca maticne otopine i promjera kristalizatora (H/T) iznosio 1.3. Mijesanje se provodilo uporabom dvaju radijalnih turbinskih mijesala (tzv. 4-SBT tip mijesala) pri onoj brzini vrtnje koja je osiguravala stanje potpune suspenzije (N = NJS). U sustavu su kontinuirano pracene koncentracija maticne otopine (uz uporabu Na-ion selektivne elektrode) te zakretni moment (koristenjem mjerila zakretnog momenta Himmelstein and C...
The influence of mixing on crystallisation is often ignored despite the fact that it affects almo... more The influence of mixing on crystallisation is often ignored despite the fact that it affects almost every aspect of the process what is especially pronounced in multiple impeller systems where flow complexity is increased. The predominant motivation for this work was to investigate the effect of mixing on nucleation kinetics of borax in the process of batch cooling crystallisation. Crystallisation was conducted in 15 dm3 crystalliser with an aspect ratio (H/dT) equal to 1.3. Such aspect ratio required an installation of a second impeller on the same shaft. Mixing was performed by using two down pumping pitched blade turbines (PBT impellers). Mother liquor was saturated at 30 °C and it was cooled down at 6°C/h. The impact of several mixing parameters, such as impeller speed, size and position, was examined. A key parameter for evaluating the blending effectiveness of stirred tanks – mixing time, was determined by potentiometric method whiles the nucleation mechanism and rate was determined using the Mersmann's nucleation criterion. Obtained results indicate that investigated mixing parameters affect the values of mixing time and consequently the nucleation kinetics. Considering the stated, by choosing proper mixing parameters, it is possible to influence the characteristic of the final product of crystallisation.
Main focus of this work was to investigate the influence of hydrodynamic conditions on crystalliz... more Main focus of this work was to investigate the influence of hydrodynamic conditions on crystallization kinetics and properties of borax crystals obtained in a 15 dm 3 dual impeller batch cooling crystallizer. The two impellers used, pitched and straight blade turbine, were mounted on the same shaft. Hydrodynamics was analyzed through the values of mixing time and specific fluid flow patterns generated. Results indicate that wider metastable zones were generally observed at impeller positions characterized by higher mixing times. In those cases, growth rate constants were lower what resulted in a formation of smaller but more regularly shaped crystals. These findings imply that dual impeller position should be taken into account in order to produce crystals of desired characteristics.
Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim mije... more Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim miješalima na kinetiku kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) tijekom njegove šaržne kristalizacije kontroliranim hlađenjem. Proces je provođen u kristalizatoru volumena 15 dm3, u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog miješala u sustav. Miješanje se provodilo korištenjem triju različitih konfiguracija dvaju miješala: PBT-PBT, SBT-SBT te PBT-SBT. Za svaku primjenjenu konfiguraciju miješala detaljno je ispitan utjecaj brzine vrtnje, promjera miješala, udaljenosti donjeg miješala od dna te međusobne udaljenosti dvaju miješala na mehanizam i brzinu nukleacije, kinetiku rasta kristala boraksa te granulometrijske karakteristike finalnog produkta. U radu je također analiziran i utjecaj brzine hlađenja matične otopine na kinetiku ispitivanog procesa. Da bi se dobio potpuniji uvid u hidrodinamička zb...
Conducting crystallization in an agitated vessel requires a proper selection of mixing parameters... more 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-dm<sup>3</sup> bench scale batch cooling crystallizer with an aspect ratio (<em>H</em>/<em>T</em>) equal to 1.3. For this reason, two radial straight blade turbines (4-SBT) were used for agitation. Experiments were conducted at different impeller spacin...
Open loop dynamic testing and closed loop automatic control have been devised, implemented and qu... more Open loop dynamic testing and closed loop automatic control have been devised, implemented and quantitatively evaluated on a portable laboratory workstation, with the aim of serving Chemical and Process Engineering students with practical training. A basic case study was conceived on level control. Classical evaluations, both qualitative and quantitative, were carried out on the dynamic response experimentally obtained on the workstation, either at open or closed loop, including the quality of the feedback action by means of the controller performance indexes (e.g., IAE; ISE; ITAE; ITSE).Although conceptually simple, the experimental activities turned out a rather demanding task in terms of time, data elaboration and interpretation work, but they provided a continuous beneficial interaction between the lecturer and the student. The developed technique, the tests with the workstation and the encouraging results obtained so far promise to be a very useful educational tool for undergra...
The aim of this work was to determine the influence of cooling rate on the nucleation and crystal... more The aim of this work was to determine the influence of cooling rate on the nucleation and crystal growth of borax decahydrate. All experiments were carried out in baffled stirred crystallizer with the volume of 2.14 dm3. Mother liquor saturated at 30 °C was cooled down at 3 different cooling rates in the range from the 4 to 9 °C/h. In order to analyze and compare the influence of fluid flow pattern in the crystallizer on product properties, examinations were performed using two different impeller types; radial straight blade turbine (SBT) and axial pitched blade turbine (PBT). Mixing with both of impellers was carried out at constant impeller speed of 300 rpm. Concentration of the solution was measured in line by potentiometric method, while the changes of crystal size over process time were determined by optical microscope and image analysis software. The nucleation and crystal growth behaviors for borax–water system in a batch cooling crystallizer were estimated according to Mersm...
Ovaj rad prilog je sustavnom inženjerskom istraživanju u marikulturi s teorijskog motrista. Temat... more Ovaj rad prilog je sustavnom inženjerskom istraživanju u marikulturi s teorijskog motrista. Tematikom pripada podrucju matematickog modeliranja b
Cilj rada je bio ispitati utjecaj hidrodinamickih uvjeta u kristalizatoru s dvama turbinskim mije... more Cilj rada je bio ispitati utjecaj hidrodinamickih uvjeta u kristalizatoru s dvama turbinskim mijesalima na kinetiku kristalizacije dinatrijevog tetr
Mnoge operacije u kemijskoj industriji u velikoj mjeri ovise o uspjesno provedenom mijesanju. Kol... more Mnoge operacije u kemijskoj industriji u velikoj mjeri ovise o uspjesno provedenom mijesanju. Koliko ce ono biti uspjesno moguce je procijeniti kroz nekoliko parametara, pa tako i kroz poznavanje vrijednosti snage mijesanja. Snaga mijesanja predstavlja energiju preko mijesala dovedenu u sustav. Njezina vrijednost, između ostalog, utjece i na velicine važne pri provedbi procesa kristalizacije kao sto su stupanj izmjesanosti te koeficijent prijenosa tvari. U ovom istraživanju, saržna kristalizacija boraksa je provedena u sustavu volumena 15 dm3 pri cemu je omjer visine stupca maticne otopine i promjera kristalizatora (H/T) iznosio 1.3. Mijesanje se provodilo uporabom dvaju radijalnih turbinskih mijesala (tzv. 4-SBT tip mijesala) pri onoj brzini vrtnje koja je osiguravala stanje potpune suspenzije (N = NJS). U sustavu su kontinuirano pracene koncentracija maticne otopine (uz uporabu Na-ion selektivne elektrode) te zakretni moment (koristenjem mjerila zakretnog momenta Himmelstein and C...
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