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Development of the Population Balance Code for Crystallization of Aluminium Hydroxide

Naderi Beni, Mahdi | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51167 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Farhadi, Fathollah; Movahedirad, Salman
  7. Abstract:
  8. Crystallization of Aluminum Hydroxide is the most important section of the Alumina production processes as the product yield and crystal size distribution (CSD) of this stage strongly affects the whole Alumina production process. In this work to simulate the crystallization in industrial steady precipitation tanks two Population Balance based models developed. First one is the Coupled CFD-Population Balance Model which considers the effects of flow hydrodynamics on crystallization kinetics and CSD. For development of this model the computational fluid dynamics software ANSYS FLUENT has been used. The two phase flow field has been simulated using Eulerian granular multiphase model coupled with a standard κ-ε turbulence model and the quadrature method of moments (QMOM) has been used to solve the population balance equations. The second model is the Homogenized Population balance Model which presumes that the solid-liquid suspension is an ideall mixture. This model is the combination of Discrete Population balance Equations and the Mass Balance Equation, which wasl coded in MATLAB computational software. The case study of this thesis is the precipitation unit of the Jajarm Alumina plant. In this unit fifteen agitated tanks were used in series to perform the precipitation. High number of grid elements, complex structure of multistage mechanical agitator and high computational load of population balances coupled with fluid dynamics cause limitations and computational costs for this simulation. Investigation of solid phase distribution in the first two tanks shows that even in low agitation rates, mixing is properly achieved. This results may differ for final tanks as crystal particles grow and agglomerate continuously. Investigation of the predicted crystal size distributions shows that although both models predict the same evolution of CSD as the agglomeration kinetics is similar, the Homogenized PB model predicts the presence of larger particles
  9. Keywords:
  10. Crystallization ; Growth ; Agglomeration ; Population Balance ; Computational Fluid Dynamics (CFD) ; Nucleation ; Aluminum Hydroxide

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