CFD applied to decanter centrifuges
Examensarbete för masterexamen
Applied mechanics (MPAME), MSc
Decanter centrifuges have become a crucial part of numerous industrial solid-liquid separation pro cesses. Its use in dewatering of municipal sewage slurries has made it an immensely valuable tool in combating water pollution. The flow and separation of various phases through a decanter centrifuge can be influenced by a host of parameters such as the slurry rheology, the solid phase size distribution, and operational parameters of the the operation such as the mass flow rate of the slurry through the machine, geometrical design features of the centrifuge and many more. The development of a feasible and reliable computational model would facilitate the qualitative testing of the influence of many of these parameters on the performance of the decanter without relying on expensive experimental tests. In this project, computational fluid dynaimcs (CFD) has been used to model the flow of municipal sewage slurry within a decanter centrifuge. A sliding mesh approach was used to model the rotation of the decanter centrifuge and a moving wall boundary condition is applied to the surface of the centrifuge drum to simulate the speed differential. The multiphase flow equations were solved by using the Eulerian mixture multiphase model by modelling the slurry as a two phase mixture of water and the heavier phase to be separated wherein the heavier phase is modelled as a relatively thick and viscous liquid. Direct validation of the developed model against experimental data was not feasible, but a qualitative judgement about the model was made based on the literature survey and the insights provided by the decanter centrifuge manufacturer. Four test cases were run on the developed model to test how it reacts to a change in certain parameters. Three of the cases test the effect of varying the heavier phase’s viscosity and the fourth case tests the model at a higher inlet mass flow rate.
Decanter centrifuge , Dewatering , Sewage sludge , CFD , Mixture multiphase