Size Reduction. By Sidra Jabeen Department of Chemical Engineering, University of Engineering & Technology Lahore . Size Reduction. Large size particles are converted into smaller particles. The process is also called as comminution. Size Reduction Methods. Compression Impact - PowerPoint PPT Presentation
Citation preview
Particle Technology
Size ReductionBySidra Jabeen
Department of Chemical Engineering,University of Engineering
& Technology Lahore Large size particles are converted into
smaller particles. The process is also called as comminution.
2Size Reduction
3Size Reduction Methods
CompressionImpact Attrition/rubbingCutting/Shear
41- Compression
Gripping + compressing between two surfacesWork done by both
surfacesFeed:Very coarseAbrasiveNon-stickyProduct: relatively
coarserExample: Nut cracker
52- Impact
Striking / collision of one body to another moving bodyGravity
impactDynamic impactFeed:BrittlehardAbrasiveHigh moistureProduct:
fines, intermediate, some coarseExample: Hammer
63- Attrition/ Rubbing
Sliding / scrubbing / rolling of material with surface or each
otherFeed:SoftNon-AbrasiveProduct: finesExample: file
74- Cutting / Shear
Slipping of planesTrimming actionFeed:DuctileFibrous Product:
definite shape / definite size no finesExample: Pair of shears
8Criteria for Comminution
Performance ParametersCapacity Energy requirementyieldIdeal
Comminution EquipmentHigh CapacitySmall energy requirement per unit
productYield a product of single size or size
distributionPerformance Evaluation:Ideal operation is taken as
standardCompare the actual with existing oneNot feasible for
crushing & grinding because of large deviationEmpirical
relations9Characteristics of Comminuted product
ObjectiveSmall particles from larger oneSmall particles are
desired Either b/c of their large surfaceOr b/c of their shape,
size & numberNon uniform product mixture of different
sizesRanging from max. particle size (coarse) to min. particle
sizeRatio of diameters of largest and smallest particle is of the
order of 104Comminuted products are smoothed by abrasion and their
size is specified10Energy & Power requirement
Cost of power and energy is major expenseMechanism involved in
size reductionMaterial feed is distorted and strainedEnergy is
stored as mechanical energy of stressAdditional force beyond
ultimate strengthFracture occur New surfaces generatedEnergyTo run
equipmentlosses
11Crushing efficiency
Efficiency = Output / InputCrushing efficiency is the ratio of
surface energy created by crushing to the energy absorbed by the
solides = surface energy created per unit areaAw = specific surface
created per unit massWn = mechanical energy absorbed per unit mass
of material
