Fluid-dynamics scale-up problems in the DTM crystallizer (original) (raw)
Related papers
Chemical Engineering Research and Design, 2005
T his work deals with the use of a compartmental model to interpret the change of the performances of a draft-tube baffled (DTB) crystallizer due to progressive scaling. The examined case was the reaction -crystallization of sodium perborate tetrahydrate. First of all, a model based on both MSMPR and PFR compartments was developed. The model was then applied to evaluate the reduction of the flow rate of the circulation stream through the draft-tube due to progressive scaling, and to predict the relevant crystallizer performances. Finally, the possibility of estimating the scaling extent in the crystallizer from the crystal size distribution (CSD) measured along the run time was shown.
Multiphase CFD modeling - scale-up of Fluidized-Bed Crystallizer
2009
Fluidized-bed crystallizers are widely utilized across numerous branches of industry. However, they have proven difficult to scale up. The present work reports the scale-up of an Oslo fluidized-bed crystallizer with a classification leg using computational fluid dynamic (CFD) methods. The apparatus was modeled in six volumes: 0.039, 0.33, 2.64, 29, 97, and 230 m 3 . Calculations cover polydispersive suspension of NaCl crystals with the initial concentration equal to 10 vol.%. Ten size classes of the crystal diameter were assumed, varying from 0.4 to 3 mm. Simulations were run using the commercial package Fluent. To model two-phase flow, an Eulerian multiphase model was used with the standard k-ε method. The chosen scale-up factor was the outlet liquor velocity. Results are compared with industrial data.
Scale-up problems in crystallizers with the draft tube and propeller
Chemik Science-Technique-Market
Streszczenie W artykule przedstawiono analizę zagadnienia przenoszenia skali na przykładzie jednego z typów krystalizatora powszechnie stosowanego w aplikacjach przemysłowych. Zdefiniowano istotny parametr procesowym, mający duży wpływ na powtarzalność technologii. Określono wymagania z punktu widzenia kinetyki procesu podczas przenoszenia skali oraz, biorąc pod uwagę najczęściej stosowaną procedurę, przeanalizowano możliwości i ograniczenia tego sposobu.
Multiphase CFD modeling: Fluid dynamics aspects in scale-up of a fluidized-bed crystallizer
Chemical Engineering and Processing: Process Intensification, 2013
Fluidized-bed crystallizers are widely utilized across numerous branches of industry. However, they have proven difficult to scale up. The present work reports the scale-up of an Oslo fluidized-bed crystallizer with a classification leg using computational fluid dynamic (CFD) methods. The apparatus was modeled in six volumes: 0.039, 0.33, 2.64, 29, 97, and 230 m 3 . Calculations cover polydispersive suspension of NaCl crystals with the initial concentration equal to 10 vol.%. Ten size classes of the crystal diameter were assumed, varying from 0.4 to 3 mm. Simulations were run using the commercial package Fluent. To model two-phase flow, an Eulerian multiphase model was used with the standard k-ε method. The chosen scale-up factor was the outlet liquor velocity. Results are compared with industrial data.
CFD simulation and comparison of industrial crystallizers
The Canadian Journal of Chemical Engineering, 2014
Simulation of flow patterns in eleven industrial crystallizers (standard Messo, Cerny direct contact, Swenson draft tube baffled, Swenson walker, Swenson evaporative, Oslo cooling, Oslo Krystal, APV Kestner, Batch Vacuum, stirred tank with disc turbine, and stirred tank with pitched blade impeller) have been carried out using computational fluid dynamics (CFD). Population balance modelling (PBM) is coupled with CFD to obtain better results. In all the cases, the crystallizer volume was 100 liter and the power consumption per unit volume was 1 kW/m 3. The simulation results have been presented in terms of mean velocity components, turbulent kinetic energy and dissipation rate. On the basis of the flow patterns, these eleven crystallizers have been compared for crystal size distribution (CSD). It was found that Swenson Evaporative, Krystal and Batch Vacuum provide relatively low CSD.
Development of Novel Crystallizer Design and Optimization Tools for Solution Crystallization
2004
Residence time distributions (RTD) are measured for both a baffled and unbaffled laboratory reactor of the same size with several internal pipes and a Rushton turbine operating at different feed flow rates and impeller rpm's. Ideal behavior as determined by the mean and the variance of the RTD was observed at an impeller Reynolds number of 2,327 for the baffled tank and 3,878 for the unbaffled tank both in the turbulent transition range. The experimental results for the baffled tank are compared to computational fluid dynamics (cfd) predictions of the RTD using k-ε turbulence model in Fluent for transitional flow regime in the tank, i.e. impeller Reynolds number between 10 and 10,000. All the qualitative aspects of the predicted RTD's are similar to those measured experimentally. The mean residence times as well as the variances of the residence time are accurately predicted by cfd in the transition flow regime.
Effect of Selected Geometry Aspects in the DTM Crystallizer on Power Input and Pumping Capacity
Chemical Engineering Research and Design, 2002
T his paper deals with the effect of draft tube shape on pumping capacity, as well as power input in a typical crystallizer with inner suspension circulation forced by means of propeller. The common theoretical relationship between the main factors affecting pumping capacity has been derived. Four types of draft tubes were considered including cylindrical and conical-cylindrical draft tube with inner and outer baf es. The investigations substantiating the theoretical considerations, were carried out for a wide range of independent variables: unit power input 0.1-1.5 W kg ¡1 ; d r =d m ratio 0.8-0.95; h r =d r ratio 0.15-0.6. The experimental data proved to be consistent with the theoretical predictions. The results make it possible to determine the best shape and the optimum location of the draft tube in the apparatus for generating the maximum pumping effect at minimum power input.
Analysis of a continuous crystallizer with agglomeration
Chemical Engineering Science, 1992
The analysis of a continuously stirred tank crystallizer in which the particles may undergo agglomeration is presented. It is shown that a solution presented previously is in error due to an assumption made in the development of the model, and that a solution in the form of a Taylor series expansion can be derived easily. The accuracy of this revised solution is determined by the number of terms used in the series. A rather large number of terms is required to generate accurate results in some cases. It is shown that physically meaningful solutions do not exist for some values of the agglomeration parameter. For acceptable values of the parameter it is shown that the particle-size distribution is monomodal.
A new model and a design procedure for an Oslo-Krystal cooling crystallizer
Journal of the Taiwan Institute of Chemical Engineers, 2015
The operation of the industrial Oslo-Krystal cooling crystallizer is simulated in this work as a continuous fluidized bed crystallizer with liquor recycling, where seed crystals are added at the top of the fluidized bed and product crystals are withdrawn at the bottom of the fluidized bed. It is assumed that the liquid phase moves upward through the bed in plug flow and the solid phase in the fluidized bed is perfectly classified. A model is developed to describe the variations of crystal size, bed voidage, crystal residence time and crystal production rate with the vertical position within the crystallizer. The effects of seed feed rate, feed solute concentration, recycle ratio and height/diameter ratio on the performance of such continuous fluidized bed crystallizer can be elucidated. A procedure based on the model can be used to rapidly design the crystallizer.
A simplified approach to the operation of a batch crystallizer
Canadian Journal of Chemical Engineering, 1990
A general model for a seeded cooling batch crystallizer based on first principles is developed, incorporating either size-dependent or size-independent growth rates. A simple approach is proposed to obtain temperature-time trajectories at constant supersaturation or nucleation rate, without resorting to optimization techniques. Cooling curves at constant supersaturation, which lead to a substantial improvement (a smaller coefficient of variation and a larger mean size) of the terminal crystal size distribution, can be determined even in the absence of precise nucleation and growth kinetics, whereas properties related to the crystal size distribution are sensitive to such kinetics. Experimental results for the potassium sulfate-water system, potash alum-water system, and hexamethylenetetramine in ethanol, methanol, and 2-propanol/water are predicted reasonably well by the model. Extension to any type of batch crystallization with super-saturation induced by means other than cooling, such as reactive precipitation and salting out, is briefly discussed.On a mis au point un modèle général pour un cristalliseur discontinu inoculé à refroidissement basé sur les premiers principes, qui utilise des vitesses de croissance dépendant ou non de la taille. On propose une méthode simple pour obtenir des trajectoires temps-température à sursaturation ou à vitesse de nucléation constantes, sans faire appel à des techniques d'optimisation. Des courbes de refroidissement à sursaturation constante, qui entra îne une amélioration substantielle (coefficient de variation plus petit et taille moyenne plus grande) de la distribution terminale de taille des cristaux, peuvent être déterminées même en l'absence de nucléation précise et de cinétique de croissance, alors que les propriétés liées à la distribution de taille des cristaux sont sensibles à ces cinétiques. Les résultats expérimentaux pour le système sulfate de potassium-eau, alun de potasse-eau et hexaméthylènetétramine dans l'éthanol, le méthanol et le 2-propanol-eau sont prédits raisonnablement bien par le modèle. On analyse brièvement la possibilité d'étendre le modèle à n'importe quelle méthode de cristallisation discontinue oú la sursaturation est provoquée autrement que par refroidissement, comme la précipitation réactive et le désalaee.