Air Classification - Comex AS
Embed Size (px)
Transcript of Air Classification - Comex AS
UCXair classifier series
The process of air classification is of critical importance formany grinding operations. Generally the overall energyconsumption for grinding can be reduced drasticallyprovided classification efficiency is high. Furthermoreproduction capacity can be significantly increased. Formany applications this is even more important than energysavings. When the purpose of air classification is toproduce different size fractions without grinding, highefficiency will be even more important in order to provideproducts of required particle size distribution.
The Comex UCX series air classifier has been developedby the mineral processing laboratory of SINTEF/NTNU inNorway to provide products in ultra fine particle sizesmainly below few microns and with high efficiency. This isachieved by a special construction which provides highcentrifugal acceleration and high dispersion of particles inthe nanometer range. This effect is achieved using low airpressure drop and rotor torque. This makes theclassification process very energy efficient. Additionally,mentioned classification efficiency is high for both ultra finesizes down to 1-2 micron range and for coarser particlesover 200-300 microns. This makes the new classifier veryuniversal and flexible. Very coarse and ultra-fine particlescan be produced efficiently in the same machine.
UCX classifiers belong to the forced vortex group ofclassifiers where the centrifugal forces are generated andcontrolled by a rotor. Forced vortex can in principle bedivided in two types.
The first type refers to the rotor operating in a significantlylarge free area with no restrictions around. In this casethe feed can be introduced into the classifier as an airsuspension, which provides good dispersion of fineparticles and thus efficient classification.
The second type of classifiers has a rotor operating insidea stator containing static diagonal blades having closedistance to the rotor and supplying the main air. In thiscase the feed is supplied as a solid material from the toppart of the rotor and is further exposed to the air flowingfrom the stator area to the rotor centre. This results ingood classification efficiency as all particles andagglomerates are exposed to significant shear forces andare close to the rotor blades. However, in thisconfiguration the feed material cannot be introduced tothe classifier as a mixture of the air and particles. Thislimits a possibility for efficient separation especially withultra fine particles which normally require very gooddispersion by mixing feed material with primary air.The new Comex UCX classifier solution combines theadvantages of both types. The table below comparesboth classifier types to the new UCX classifier.
Operating principle of the UCX classifier
UCX classifier cross section
In the UCX air classifier the feed material enters theclassifier unit mixed with the air stream by a tangential inletat the top part of the classifier. In this area the feed materialis well dispersed in the air. At this stage the firstclassification step takes place around the upper part of therotor where very fine particles are removed from the feedmaterial within relatively short time period. The coarseparticles and those which are slightly finer than the cut pointare forced to flow through the narrow opening between therotor and the static blades. Behind those blades another airflow is introduced (secondary A). In this area particlesslightly finer than the cut point are exposed to significantshear forces close to the rotor.
Consequently these particles end in the finer materialfraction and only coarser ones proceed to the lower coarsefraction outlet. Additionally, there is another secondary airflow applied below the rotor (secondary B) providinga possibility to rinse the coarse particles from the finegrains agglomerated on their surface. In addition it reducesthe sedimentation velocity of the particles in bothclassification zones which is critical to obtain optimalconditions. This configuration combines the best of the twooperating principles considered originally and hastherefore a superior performance.
Feed material mixed with primary air
Efficient classification of ultra-fines
Efficient classification in the wide size rangefrom ultra-fines to coarse sizes
Perfomance at high capacity
Efficient classification of fine particles closein size to the cut point
Classifier withstatic blades
Performance limitations for conventional forced vortex classifier types and the UCX
The most important design features which makethis classifier unique are:
Pneumatic transport of the feed material to the classi-fier, which provides excellent dispersion of the materialin the air during a turbulent flow inside the inlet pipe
Preliminary classification of ultra fines in the upperclassifier zoneFinal classification of the middle size particles in thesecond classifier zoneLack of collisions between the entering trajectories of thefeed and the descending coarse stream inside theclassifier. This prevents mixing of the fine particles fromthe feed stream with the coarse particles flowing to theclassifier outletSpecial rotor geometry and angular blade position makeit possible to achieve much finer products than withtraditional construction
Exchangeable rotor bladesSimple rotor replacement through the inspection windowon top of the classifierCompact design
Tangential feed inlet providing preliminary particleacceleration which reduces wear rate of the rotorblades
The main fine fraction outlet is spiral shaped, hencekinetic energy of rotating particles and air molecules iseasily transferred to positive displacement at the outletpipe. This is of critical importance, providing lowerpressure loss during classification
UCX 750 classifier unit
High classification efficiencyLarge processing capacity from smaller unitsUltra-fine cut size down to d97 of 1.5 micronsHigh efficiency in very wide product range from1.5 to 300 micronsLow pressure loss and power requirementLow wear rate of the moving partsReduced maintenance and operating cost
Comex UCX air classifiers have different rotor sizes,ranging from 200 mm diameter up to 1700 mm diameter.Production capacity ranges from 1200 kg/h to 100 t/h.Tables below show the range of classifiers including themost important operating and construction parameters.The UCX 200 is used in pilot plants for carrying out smallscale investigations or for classifying the finest ofproducts.
UCX classifier weights and dimensions
This results in the following benefits fromapplication of the Comex UCX air classifier:
UCX classifier technical specifications
Air flow rate
Product particlesize d97
0.3 - 1.2
1.8 - 7.5
7 - 30
15 - 75
4 - 18
10 - 50
20 - 100
- fan motor power depending on classifier circuit configuration- capacity depending on product properties and particle size produced
UCX 350during testing
Rubber lined UCX 350 rotor
Energy saving potential
UCX air classifier provides high classification efficiencyand simultaneously gives a very low pressure loss duringoperation. This is of critical importance when the overallenergy for material processing is considered. Applicationof the UCX classifiers in many industrial grinding circuitsprovided significant benefits in form of