LUM will present at the exhibition
Booth G5
and give 4 presentations on different topics
Accelerated screening by multisample analytical centrifugation for selection of flocculants and demulsifiers
T. Sobisch*, D. Lerche
Selection of flocculants and demulsifiers is a frequent challenge. It relates to remedy of settling issues and to the optimization of separation processes in fields like wastewater treatment and crude oil processing.
Multisample analytical centrifugation based on STEP-Technology offers a unique option for screening for the optimal product, additive concentration and separation conditions. Not only the degree of separation but also separation kinetics and the residual turbidity can be determined with high throughput by comparison of 12 samples under identical conditions in 1 run.
The potential of this approach is demonstrated by case studies for the selection of flocculants for centrifugal dewatering of wastewater sludges and for selection of optimum demulsifier selection for crude oil dewatering.
Keywords: additive screening, flocculant selection, demulsifier selection, dewatering efficiency, separation velocity, analytical centrifugation
Measurement of x ray profiles – a new method for the evaluation of separation behaviour of concentrated nontransparent dispersions
A. Zierau*, A. Fedur, T. Sobisch, D. Lerche
Detailed evaluation of the separation behaviour of dispersion is problematic for concentrated nontransparent dispersions. It is difficult to define a separation level or to trace differences in solids concentration along the liquid column.
Measurement of space and time resolved x ray transmission profiles offers a unique solution to this problem. This approach can even be used to determine concentration gradients in sediments, which is of great importance for separation unit processes like filtration, settling and centrifugation. Even more information about the structure of sediments can be used to deduce the nature of particle interactions and to determine the degree of flocculation.
The method can be applied to determine the kinetics of separation processes or to determine the concentration distribution obtained after separation, i.e. after settling, centrifugation, filtration.
The measurement technique and its application for different systems like mineral suspensions and emulsions is introduced.
Keywords: x-ray, dispersion structure, suspensions, emulsions, separation analysis, sediment profiles
Separation and consolidation behaviour of flocculated versus non-flocculated dispersions: A reliable laboratory classification test
T.Sobisch, A. Zierau, D.Lerche*
LUM GmbH, Berlin/Germany
Flocculation behaviour is important in many technical applications and especially in solid-liquid separation. While for some applications sedimentation and consolidation have to be avoided or minimized, for solid-liquid separation these are essential. Often the value of Zeta-potential is employed to judge the state in the sense of flocculated versus non-flocculated dispersions. But this approach is often not applicable especially in case of sterically or rheologically stabilized dispersion. There is a need for fast reliable methods for comprehensive characterization of flocculation processes.
Analytical centrifugation based on Space and Time resolved detection of Extinction Profiles of electromagnetic waves (STEP-Technology) over the entire sample height was used to characterize the nature of particle interactions and the degree of flocculation in dispersions at original concentration. Photometric and x-ray measurements were carried out.
Investigations on sedimentation and consolidation behaviour of flocculated polydisperse suspensions of different suspensions made from quartz, lime stone, titanium oxide, magnetic therapeutic carrier particles and enzyme coated nanoparticles are presented to demonstrate the procedure. Colloidal stable dispersions (stable against flocculation, agglutination) show typical polydisperse sedimentation behaviour, whereas flocculated dispersions exhibit zone sedimentation and gradual consolidation. While the packing density for colloidal stable dispersions does depend only slightly on the excess pressure acting on the sediment it strongly depends on pressure for flocculated dispersions and it takes much longer to reach corresponding equilibrium packing density. Instead of carrying out measurements at different accelerations it is also possible to evaluate the compressibility of sediments (or cream layers) by increasing the acceleration step-wise and recording the kinetics of the sediment (cream layer) height or packing sediment concentration. It was shown that in all investigated suspensions the state of flocculation was correctly classified even at very high concentration but e.g. in case of polymer stabilized magnetic micro- and nano-particles high Zeta-potential (40 - 60 mV) would lead to false “non-flocculated” classification.
Keywords: flocculation state, analytical centrifugation, Zeta-potential, coated nanoparticles, compressibility, sediment density, emulsions, suspensions, sedimentation, creaming
Is it possible to reduce costs for pilot centrifuge testing by lab scale tests?
T. Detloff*, S. Küchler, T. Sobisch, D. Lerche
Unit processes using centrifugal fields are often applied for separation and classification of diverse materials. Modelling of these processes requires information about the separation behaviour of the suspensions to be processed. To this end direct measurements in centrifuges are obligatory for the dimensioning of the separation units to obtain the desired cut-off size and residual effluent turbidity. Moreover, these measurements have to gather kinetic information as function of the processing conditions, viscosity behaviour, particle interaction and particle concentration of the product. Results of measurements at earth gravity cannot be scaled up to reflect the situation in a centrifugal field.
A multisample analytical centrifugation technique with photometric detection is presented which allows a comprehensive characterization of separation processes in the centrifugal field at lab scale with high sample throughput. In particular the type of sedimentation behaviour (free sedimentation of individual particles, hindered settling, zone settling) can be deduced from the progression of the transmission profiles. Even more it can determine the critical residence time as function of feed concentration for a desired effluent clarity and allows measuring the velocity distribution of particles inside the centrate in-situ.
Approaches for dimensioning the centrifugation at larger scale based on these in-situ at labscale available data are discussed.
Keywords: process optimization, solid-liquid separation, liquid-liquid separation, process design, decanter centrifuges, analytical centrifugation
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