Paper on-classification-and-classifiers
- 1. Classification and classifier April 8 2013 The paper on classification and classifier gives the basic idea about the particle size separation method using the principle that different particles have different settling velocity in a fluid medium (water) by the process called classification. There are four types of classifier- 1.Mechanical, 2. Hydraulic, 3. Hydro clone and 4. Centrifugal air classifiers whose working and construction along with principle, features, benefits, etc. are described. Subodh Rana (367/11) Md Salim (360/11) Chandan Kumar (420/11)
- 2. Paper on Classification and Classifiers Classification Classification is basically a particle size separation method. Classification may be defined as the separation of solid particles into two or more products according to their velocities when falling through a fluid medium generally water is used as fluid medium. Range of particles size: 1µm -800µm. Velocity of particles depends on their size, shape and density. Particles with higher density and larger size will settle down quickly as compared with particles with lower density and smaller size. Limestone, cement, coal industry performs dry classification for separation of fine particles in which air is used as fluid medium. Classifier A classifier is a machine which actually performs process stated above called classification. Types of classifier a) Mechanical Classifiers(Spiral classifier) b) Hydraulic Classifier c) Hydro cyclone Classifier d) Centrifugal air classifier Principle of classifier It is based on the different settling velocity of particles in water.
- 3. MECHANICAL CLASSIFIERS There are many mechanical classifiers but the two most famous are Rake classifier and Spiral classifier. Construction and working Mechanical classifiers consist of a settling tank with parallel sides and inclined base, there is a device inside it that facilitates agitation of the pulp and removal of the settled solid. The feed pulp is fed into the classifier, solids with high settling velocity settle at the base of the tank and mechanical rakes and spirals (helical screws) take away the settled solid from bottom to top and at the same solids with low settling velocities come out through the water overflow. Particle Size: - 800-75 microns Fig. showing spiral classifier at work
- 4. Fig. showing working sketch of mechanical classifier Main features Adjustable weirs Sealed, submerged bearing Single spiral range 30cm-220cm Overflow collection box Main benefits Energy saving Powerful self-contained spiral lifting device Continuous spiral raking
- 5. HYDRAULIC CLASSIFIER Hydraulic classifiers use the principle of hydraulics and different settling velocity of solids Construction and Working Hydraulic classifiers consist of settling cones which are conical vessels, where pulp is introduced vertically from the top. Coarse particles settle down and leave the vessel through the underflow spigot; fine particles leave the vessel with most of the water overflows. Hydraulic classifiers consist of a series of column in which water current is injected from bottom which moves upward and takes away the lighter particles of low settling velocity. Hydraulic classifiers are widely used in sand and glass industry. Particle size: - 2µm-7µm Fig showing hydraulic classifier
- 6. Fig. showing working of a hydraulic classifier Main Features and benefits Used for 2-7µm size particles Series of columns are used
- 7. HYDROCYCLONE CLASSIFIER Hydro cyclone classifier is widely applied in mineral processing for fine classification (mostly <100µm), often in a closed-circuit with ball mills for flotation or leaching feed preparation and for special fine final products (kaolin). They are particularly efficient for fine separation sizes. Construction and Working A hydro cyclone is a vessel composed of a cylindrical section with a tangential feed entrance, joined to a lower conical part. The feed is accelerated and rotates at high speed within the vessel, transporting the coarse particles by centrifugal forces to the inner wall, from where it moves down along the conical part and leaves the vessel through the underflow spigot. The slower settling fine particles stay in the centre of the fluid, which forms an inner upstream current and leaves the vessel through the central upper discharge opening. To avoid short-cuts, the upstream is collected by an adjustable inner piece of pipe, connected to the overflow outlet. Particle size: -1-100 µm Fig showing a hydro cyclone Main Features and benefits: - Mild steel construction Maximum operating pressure of 10 kg/cm2 Efficiently removes fine sand and silt particles of size higher than 75 microns and specific gravity more than 2.65.
- 8. Used in micro irrigation systems to remove sand and silt particles from irrigation water. Dirt can be easily flushed out through dirt collection chamber. Easy to clean and maintain. CENTRIFUGAL AIR CLASSIFIER These classifiers use centrifugal forces, similar to cyclones, to separate particles at cut points between 15 and 100 microns. Construction and working The feed material is carried into the classifier by the primary inlet flow stream. Internal baffles apply drag forces to the coarse particles while allowing air to pass through them for separation of the fines. The heaviest particles drop to the bottom of the classifier and are discharged through a valve. Prior to discharge, a secondary air stream enters into the bottom of the classifier and passes through the material. Particles near the cut point in size are returned to the classifier chamber. The air stream carrying the fine particles follows a spiral path to the outlets on each side of the unit. The two air streams combine and enter a cyclone for final recovery of fine particles. A manual adjustment to the secondary air damper will provide a change in the size of the fines being separated. Because there are no moving parts within the material flow stream, the need for maintenance is minimized. Particle size: - 15-100microns
- 9. Fig. showing mechanism of Centrifugal air classifier Main features and benefits Wide range of cut point adjustability between 15 to 100 micron range Increased throughput compared to dynamic rotary classifier, lower maintenance cost High efficiency separation Classifier has no moving parts Cut point adjustability using interchangeable orifices and secondary air Virtually no internal parts within classifying material flow stream Low cost alternative to dynamic rotary classifier Internal Lining – AR Plate or Ceramics available for high abrasive applications