Hydrodynamics of solid-liquid fluidized beds: modelling and experimental studies

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dc.contributor.advisor Joshi, Jyeshtharaj
dc.contributor.advisor Padhiyar, Nitin
dc.contributor.author Ghatage, Swapnil V.
dc.date.accessioned 2015-04-21T16:28:01Z
dc.date.available 2015-04-21T16:28:01Z
dc.date.issued 2014
dc.identifier.citation Ghatage, Swapnil Vilasrao (2014).Hydrodynamics of solid-liquid fluidized beds: modelling and experimental studies (PhD Thesis). Indian Institute of Technology, Gandhinagar, pp.289 (Acc No: T00055) en_US
dc.identifier.uri https://repository.iitgn.ac.in/handle/123456789/1693
dc.description.abstract Fluidized beds are widely used in chemical, petrochemical and process industries. They are preferred over other reactors for carrying out various gas‐solid, solid‐liquid and gas‐solid‐liquid processes due to enhanced contact between the fluid and solid particles. However, the efficient operation of a fluidized bed requires the accurate choice of design and operating conditions and the accuracy of prediction of fluidization behaviour. With the developments in sophisticated measurement techniques and computational methods as well as increasing computational power, the detailed study of fluidized bed hydrodynamics is increasing extensively. In view of this, as a first exercise, the published literature on the hydrodynamics of these equipment has been systematically analyzed. The advances made in the experimental, modelling and simulations have been critically reviewed. The present status of application of computational fluid dynamic (CFD) simulations has been brought out. In three‐phase sparged reactors such as fluidized beds and slurry bubble columns, gas is sparged in the form of bubbles. The gas phase flows in one of the two hydrodynamic regimes namely homogeneous or heterogeneous. The performance is known to depend strongly on the regime of operation. The estimation of critical gas holdup at which transition from homogeneous regime to the heterogeneous regime occurs is crucial for the design and scale‐up of sparged reactors. A number of experimental and empirical studies are published in the literature; however, there exists a need of studies on athematical modelling. In the present work, the theory of linear stability has been used to develop a mathematical model for the prediction of regime transition over a wide range of bubble size (0.7 to 20 mm) and terminal rise velocity (80 to 340 mm/s), particle settling velocity (1 to 1000 mm/s), particle concentration (0.0007 to 30 vol%) and slurry density (800 to 5000 kg/m3). It was observed that the developed model predicts the transition gas holdup within a standard deviation of 12 per cent for three‐phase sparged reactors. It was also observed that the developed generalized stability criterion predicts the regime transition in gas‐liquid two‐phase systems satisfactorily within 10 per cent. In multiphase systems involving a dispersed phase, such as fluidized beds, the interphase exchange of mass, heat and momentum transfer can be very different from those from a single particle, droplet or bubble moving under terminal conditions. However, most existing methodologies still rely heavily on empirical relationships. In this study the hindered settling/rising (slip) velocity of single steel particles (dPD = 5 to 12 mm) and single air bubbles (dB = 1 to 4 mm) has been measured in a solid‐liquid fluidized bed of uniform size borosilicate glass beads (dP = 5 and 8 mm) as a function of superficial liquid velocity. The homogeneity and intensity of the turbulence within the fluidized bed has been quantified using article image velocimetry (PIV) and on the basis of the classification velocity of the foreign (steel or bubble) particle. It was found that the turbulence resulted in an increase in the computed drag coefficient under all the experimental conditions covered in this work. Eulerian‐Eulerian simulations of a monodisperse solid‐liquid fluidized bed (SLFB) have been carried out to study the effect of turbulence in SLFB on motion of the settling particle. The motion of foreign settling particle has been studied by the dynamic mesh technique provided in FLUENT 14.0. The results show that the model can satisfactorily predict the terminal settling velocity at lower fluidization. The possible reasons for deviations at high voidages have been explained. Also, computational fluid dynamics‐discrete element method (CFD‐DEM) has been applied for the simulation of the motion of foreign dense particle introduced in a onodispersed SLFB. The fluidization hydrodynamics of SLFB, settling behaviour of the foreign particle and particle‐particle collision effects have been investigated. Compared to those predicted by empirical correlations, the particle classification velocity predicted by CFDDEM provided better agreement with the experimental data (less than 10% deviation). The dimensionless collision frequency obtained by CFDDEM was found to agree with those predicted by the kinetic theory for granular flow (KTGF). The particle collision frequency was found to increase with an increase in the particle size ratio (dPD/dP) and become independent of the foreign particle size for high solid fractions. A correlation describing the collision force as a sole function of the average bed voidage was developed having a maximum error less than 20% in the prediction of particle collision force for dPD/dP ≤ 2. In many industrial‐scale fluidized‐bed reactors, particle mixing and segregation play a vital role in determining the reactor performance. However, there exists a lack of studies wherein the fluidization of systems involving more than two types of particles is involved. Such systems are of high industrial importance in mineral and chemical process industries. Therefore, it was thought desirable to study the coupling between superficial liquid velocity and a multi‐size (and/or multi‐density) particle systems consisting of more than two types of particles. In the present work, Eulerian‐Eulerian simulations have been carried out to investigate the effect of particle density and diameter on the minimum fluidization velocity, segregation and intermixing behavior in a fluidized bed comprising of three to five different types of solid phases. It was observed that the Eulerian‐Eulerian model can satisfactorily predict the fluidization characteristics in multi‐component fluidized bed including the minimum fluidization velocity. The stability analysis of multiphase reactors has been the focus of research for the past few decades. In the present work, the regime transition in SLFB has been analyzed using various experimental (PIV and measurement of settling velocity) and modelling (1D linear stability, 3D CFD and 3D DEM) methods. The characterization of turbulence in SLFB through these methods has been used to provide an insight into the mechanism of momentum transport and hence the transition. The transition conditions obtained using different approaches have been compared. The relative advantages and limitations of each method have been clearly brought out. Recommendations have been made for the estimation of some of the design parameters for SLFB. Suggestions have been made for the future work in the area of experimental and modelling studies. en_US
dc.description.statementofresponsibility by Swapnil Vilasrao Ghatage
dc.format.extent xxxviii, 289 p.; col.; ill; 24 cm. + 1 CD-ROM
dc.language.iso en en_US
dc.publisher Indian Institute of Technology, Gandhinagar en_US
dc.subject Solid-Liquid en_US
dc.subject Hydrodynamics en_US
dc.subject Petrochemical and process en_US
dc.subject Computational fluid dynamic (CFD) en_US
dc.subject Fluidized beds en_US
dc.subject Solid‐liquid fluidized bed en_US
dc.subject Kinetic theory en_US
dc.subject Modelling studies en_US
dc.title Hydrodynamics of solid-liquid fluidized beds: modelling and experimental studies en_US
dc.type Thesis en_US
dc.contributor.department Chemical Engineering
dc.description.degree Ph.D.

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