Dynamic Simulation of Mechanical Solid-Liquid Separation in Centrifuges

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The following sub-project Dynamic Simulation of Mechanical Solid-Liquid Separation Centrifuges deals with the development of a dynamic process model for flowsheet simulations of the separation behaviour and dewatering in continuous centrifuges. During the first two funding periods, material functions for the settling behaviour, the sediment build-up and solids transport of PVC were experimentally investigated. The investigations for the sediment build-up of PVC show incompressible material behaviour with an approximately constant porosity of the saturated cake. In addition to the laboratory tests for the material, experiments for the stepwise change of process conditions and machine parameters for a lab-decanter centrifuge verify a correlation between transient changes of the separation behaviour and the residence time distribution of the liquid. The results yield in a dynamic process model. The approach connects the separation behaviour, residence time distribution and the solids transport by the screw conveyor system with the material properties. The basis of the modelling is the interconnection of different compartments. This allows the solution of local distributed material properties. Moreover, the presented approach combines the settling behaviour with the sediment transport by correcting the volume of the separation zone by considering the sediment radius. In the third funding period, the dynamic process model will be extended by the dewatering of coarsely-dispersed particles, the consolidation behaviour of flocculated suspensions and the flowsheet simulation for the inter-connection between precipitation and solid-liquid separation. A lab centrifuge is used for determining the kinetics of the dewatering process. The cake transport in the conical part of the machine and the dewatering kinetics reveal in the dynamic process model for dewatering. Flocculated particles exhibit a completely different material behaviour for the sediment build-up. The porosity of the cake depends on the compressive yield stress, which is measured in a lab centrifuge. The experimental investigation reveals in the material function for the compressive yield stress. Furthermore, the conveyability of a saturated cake depends on the shear stress and the yield point. Both are measured in a ring shear tester and are combined with the compressive yield stress in the dynamic process model of flocculated slurries in decanter centrifuges. Cooperation with the group of AG Kind for the flowsheet simulation of precipitation and decanter centrifuge will be exhibit the efficiency of Dyssol. This includes the inter-connection of precipitation and solids-liquid separation by taking a tear stream of the fines into the precipitation reactor into account and. This results in a completely coupled dynamic flowsheet of the overall process.