CFD Modelling of Decantation Drums EVALUATED
In this master's degree thesis, multiphase modelling of horizontal decanters is carried out using CFD. Decanter is a kind of equipment very common in the separation of immiscible liquids. In this work, it is used in a process dedicated to Biodiesel production, namely for the separation of glycerine from methyl ester. Other mechanical or non-mechanical technologies exist that allow the improvement of the separation but none is as simple as gravity separation. A section is devoted to review other technologies for example: microwaves, electrocoalescers and ultrasounds. Concerning gravity separation, the main mechanisms that take place in a decanter are reviewed: sedimentation or gravity settling and coalescence and break-up. The formation of emulsions and their stability are also briefly discussed. CFD allows the detailed computation of the internal flow in the decanter. Two different methods were used for the multiphase modelling: VOF (Volume of Fluid) and DPM (Discrete Particles Method). The first allows to track the interface between the two phases, the second allows to model the dispersed phase as non deformable particles and analyse their motion. DPM is more helpful for separation efficiency estimation and analysis where VOF model is used for asserting the stability of the interface. The results obtained show that preferential passages exist inside the simulated decanters. It means lower separation efficiency for these decanters. However, it is proven that with minor modifications like the addition of a baffle inside the decanters, separation efficiency can be increased as much as 15%.
Setembro 6, 2007, 17:0
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