Hydrocyclones centrifugal sedimentation

Prethickening of filter feeds can be done with a variety of equipment such as gravity thickeners, hydrocyclones, or sedimenting centrifuges. Even cake filters can be designed to limit or completely eliminate cake formation and therefore act as thickening filters and be used in this thickening duty. 

Gravity and centrifugal sedimentation can be combined for the same sample in order to directly determine Stokes diameter for a wide range of particle sizes. In such a way conversion are avoided and a mass distributions, applicable to processes where gravimetric efficiencies are relevant, can be properly derived. Ortega-Rivas and Svarovsky (1994) determined particle sizes distributions of fines powders using a combined Andreasen Pipette-pipette centrifuge method. They derive relations useful to model hydrocyclone separations, which were later employed to describe apple juice clarification. 

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). 

For any separator with a size-dependent performance, such as a hydrocyclone, a sedimenting centrifuge or a settling vessel, the grade efficiency varies with particle size, and a graphical representation of this is called the grade efficiency curve (see section 3.2.2). As the value of the grade efficiency has the character of probability, it is sometimes referred to as the partition probability the curve then becomes the partition probability curve or Tromp curve. 

Thirdly, there are those chapters which only needed minor updating and amendments. These include Characterization of Particles Suspended in Liquids, Efficiency of Separation of Particles from Fluids, Hydrocyclones, Separation by Centrifugal Sedimentation, Filtration Fundamentals, Methods for Limiting Cake Growth, Pressure Filtration, Particle-Huid Interaction, Thermodynamics of Solid-Liquid Separation. 

The size corresponding to 50% on the reduced grade efficiency curve G (x) is referred to as the "reduced cut size" - see Fig.l. Most mathematical descriptions of the performance of hydrocyclones or sedimenting centrifuges are in terms of the reduced cut size. 

The reduced grade efficiency curves of some dynamic separators, including hydrocyclones and sedimenting centrifuges, can be fitted by a cumulative log-normal function in the following form ... 

The capacity of filtration centrifuges is very dependent on the solids concentration in the feed. For example, at 10 per cent feed slurry concentration 9 kg of liquid will be centrifuged for every 1 kg of solids separated whereas with a 50 per cent solids concentration the quantity will be less than 1 kg. For dilute slurries it is well worth considering using some form of pre-concentration such as gravity sedimentation or a hydrocyclone. 

The degree of cell separation is an important parameter to be evaluated in perfusion systems. This can be done through the use of some concepts as cell separation efficiency, grade efficiency, and cut size. These concepts are applicable to any equipment whose performance remains constant if the operational conditions do not change. They are valid, therefore, for equipment such as sedimenting centrifuges, hydrocyclones, gravitational settlers, etc. 

Sedimenting centrifuges Filtering centrifuges Hydrocyclones Deep-bed filters Cartridge filters Pressure vessel filters Filter presses Continuous filters Gravity separation equipment... 

To recover liquid in order of preference of settlers, Section 5.8, thickeners. Section 5.10 and sedimentation centrifuges. Section 5.12 clarifier, settler, washing tray thickener, reactortubular bowl centrifuge, batch automatic (horizontal or vertical bowl, disc with intermittent nozzle discharge) continuous disc bowl centrifuge with nozzle discharge. 

Mechanical separations Gravity Centrifugal force Pressure Heterogeneous Sorting (s - s) Dense-media separation (s — 1) Flotation (s — 1 — g) Sedimentation (s — 1) Filtration (s — 1) Pressing (s — 1) Centrifugation (s — 1) Hydrocyclone separation (s — 1) Classification Sieving (s — s) Air classification (s — g) Hydraulic classification (s — 1)... 

Hvdrocvclones use centrifugal force to separate sediments. A hydrocyclone consists of a cone-shaped vessel into which a slurry is fed tangentially, thereby creating a vortex. Heavier particles settle and exit at the bottom while water and s iments exit through an overflow pipe. Hydrocyclones may be useful where a sharp separation by particle size is needed. 

Gravity sedimentation equipment, hydrocyclones, sedimenting centrifuges or flotation cells have also been extensively used in mineral processing for separation of minerals according to density or affinity to water. In such separations, the efficiency is expressed by the Tromp curve which, similar to the grade efficiency curve, shows probability of separation as a function of material density or mineral composition. The steepness of the curve is a measure of the sharpness of the separation. 

As was stated in the introduction, Stokes diameter jcst is usually used to characterize particle size in those applications where it is the behaviour of particles in liquids that determines the separation efficiency and other operational characteristics of the separators (e.g. in sedimentation, centrifugation and hydrocyclones). Methods that measure Stokes diameter, such as sedimentation or fluid classification, have therefore been used extensively in this field. Although preference is naturally given to wet methods, air classification is also widely used. 

Gibson, K., Large scale tests on sedimenting centrifuges and hydrocyclones for mathematical modelling of efficiency Proc. of the Symposium on Solid—Liquid Separation Practice, Yorkshire Branch of the I. Chem. E., Leeds, England, March 27-29 (1979), pp. 1-10... 

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