Concentrator, centrifugal sedimentation

The original procedure from which the Formalinethyl acetate centrifugal sedimentation technique was adapted was the Formalin-ether concentration method of Ritchie. Hie Formalin-ethyl acetate procedure avoids problems with the flammability and storage of ether. This procedure can be performed on specimens which have been fixed in Formalin for a time or on specimens with Formalin added during the processing. The procedure can also be performed on material fixed in MIF. 

Yeast separation and concentration. Extraction of ethanol from biomass requires several separation steps, traditionally by centrifuging, sedimentation and cake filtration. First, after the fermentation, the yeast is removed from the fermentation broth and may be recycled. Additionally, after ethanol is stripped from the fermentation broth by steam followed by the removal of solid fractions, the remaining material called the thin stillage can be clarified for reuse upstream as the process water. 

Sedimentation The settling of suspended particles or droplets due to gravity or an applied centrifugal field. The sedimentation rate (or velocity) divided by acceleration is termed the sedimentation coefficient. The sedimentation coefficient extrapolated to zero concentration of sedimenting species is termed the limiting sedimentation coefficient. The sedimentation coefficient reduced to standard temperature and solvent is termed the reduced sedimentation coefficient. If the sedimentation coefficient is... 

Diffusion is driven by a concentration gradient sedimentation is driven by a centrifugal field. Why should the transport coefficient ratio s/D depend only on nontransport quantities ... 

Some advantages of disc centrifuge sedimentation method include (1) the disc centrifuge allows a wide dynamic range of particle size analysis, depending on particle density, from 30 jun down to 0.01 pm (2) any particle which can be centrifuged can be analysed (3) large representative sample (lO particles) (4) requires only 0.5-1.0 ml sample of 0.05-0.5% concentration. 

Cyclones designed for use with liquids are referred to as hydrocyclones, hydraulic cyclones or hydroclones. The basic principle employed to effect either concentration or classification of the solids is centrifugal sedimentation, caused by introducing the feed suspension tangentially into the unit they are particularly attractive for many applications because they have no moving parts. Specific aspects of design are provided by Svarovsky (1984). 

A low-concentration suspension of clay (density 2640 kg m ) in water with a viscosity of 0.001 Ns m and density 1000 kg m is to be separated by centrifugal sedimentation. Pilot runs on a laboratory tubular bowl centrifuge operating at 20000 rev. min indicate that satisfactory overflow clarity is obtained at a throughput of 8 x lO- m s-. ... 

In centrifugal sedimentation, a complication arises because the particle velocity depends on not only particle size, as in gravitational sedimentation, but also the radial position of the particle. As Equation 34-14 shows, the particle velocity increases with increasing radial distance r from the axis of rotation. Because of this, the particle concentration below the measurement zone decreases exponentially with the sedimentation... 

If a sedimentation experiment is carried out long enough, a state of equilibrium is eventually reached between sedimentation and diffusion. Under these conditions material will pass through a cross section perpendicular to the radius in both directions at equal rates downward owing to the centrifugal field, and upward owing to the concentration gradient. It is easy to write expressions for the two fluxes which describe this situation ... 

The Z-concept permits scale-up between sinulat centrifuges solely on the basis of sedimentation performance. Other criteria and limitations, however, should also be investigated. Scale-up analysis for a specified sohds concentration, for instance, requires knowledge of sohds residence time, permissible accumulation of sohds in the bowl, G level, sohds conveyabihty, flowabihty, compressibihty, limitations of torque, and sohds loading. Extrapolation of data from one size centrifuge to another calls for the apphcation of specific scale-up mechanisms for the particular type of centrifuge and performance requirement. 

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