LUM GmbH Presentations at the 9th World Filtration Congress

LUM GmbH Presentations at the 9th World Filtration Congress

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Presentations

Lecture: session 414, Thursday April 22nd, 2004; T. Sobisch, D. Lerche
"Use of Analytical Centrifugation for Evaluation of Solid-Liquid Separation in Decanter Centrifuges: Application for Selection of Flocculants for Sludge Dewatering"

sludge dewatering preprint 1 Chemistry Preprint Archive, Volume 2002, Issue 10, October 2002, Pages 1-11
sludge dewatering preprint 2 Chemistry Preprint Archive, Volume 2002, Issue 4, April 2002, Pages 265-274

The paper reports on a new laboratory method for evaluation of solid-liquid separation in decanter centrifuges based on analytical centrifugation. The method allows to determine the two critical parameters for sludge dewatering – separation rate of sludge flocs and the compressibility (dewaterability) of the sludge cake.
The initial separation rate gives information whether or not the sludge flocs are separated fast enough from the bulk liquid. This relates to the maximum throughput performance at which the decanter can operate. The final cake solids obtained by centrifugation measures to what extent the separated sludge cake can be compressed. This is proportional to the total solids, which can be obtained in the decanter if throughput rate is not critical.
The action of high shear stresses during mechanical processing was modelled by adapting the sample pre-treatment, so that similar changes take place in the sludge samples as in practice.
The performance of the newly developed method was demonstrated by investigations on the effect of the feed solid concentration, of mechanical stresses on sludges before flocculant addition, by an example of flocculant selection and by comparison with results obtained under field conditions.

Poster session: 146, Monday April 19th, 2004; D. Lerche, T. Sobisch
"Characterization of Sedimentation and Consolidation Behaviour of Concentrated Dispersions by Analytical Centrifugation"

The sedimentation and consolidation behaviour of suspensions was experimentally analysed by means of a multisample analytical photocentrifuge. Experiments were conducted covering a broad range of volume concentrations and centrifugal accelerations. The obtained material functions allow to simulate batch sedimentation, filtration and consolidation.
For only hydrodynamically interacting particles the separation velocity decreases with the volume concentration. The so-called hindered settling rate may be fitted to a power law. For rigid spherical particles the exponent was found to be in the range of 3 to 4.6 in dependence on the Reynolds number of the settling particles. In turn the description of sedimentation and packing of deformable particles is possible by using a deformation parameter and the maximum packing density as fitting parameter. The flexible shape leads to an overall lower viscosity. For both rigid and deformable particles theoretical description and experimental results are in excellent agreement.
Interacting particle systems above the gelpoint have to be described by the compressive yield stress. The compressive properties of stable and flocculated dispersions can be easily determined by multisample analytical centrifugation for rapid classification and tailoring of dispersion properties.