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Microsoft PowerPoint - L2 UTS 49316 autumn 2018 material handling A .pptx 25/03/2018 1 UTS 49316 Material Handling Week 2 : Lecture 2 2 Characterisation of Bulk Materials 25/03/2018 2 3 Solids Handling and Processing Identification of Key Properties (Particle/Bulk Characteristics) Confident, Accurate, Reliable & Optimal Design and Operation 4 Characteristics And Classification Of Materials • Method to be adopted and selection of equipment for a materials handling system primarily depends on the type of material/s to be handled. • It is, therefore, very important to know about different types of materials and their characteristics which are related to methods and equipment used for their handling. • Basic classification of material is made on the basis of forms, which are (i) Gases, (ii) Liquids, (iii) Semi Liquids and (iv) Solids. • Solids form the majority of materials which are handled in industrial situation. Solids are classified into two main groups: Unit load and Bulk load (materials). 25/03/2018 3 5 • Bulk materials are those which are powdery, granular or lumpy in nature and are stored in heaps. • Example of bulk materials are: minerals (ores, coals etc.), earthly materials (gravel, sand, clay etc.) processed materials (cement, salt, chemicals etc.), agricultural products (grain, sugar, flour etc.) and similar other materials. • Major characteristics of bulk materials, so far as their handling is concerned, are: lump-size, bulk weight, specific weight, moisture content, flowability (mobility of its particles), angles of repose, abrasiveness, temperature, proneness to explosion, stickiness, fuming or dusty, corrosivity, hygroscopic etc. 6 25/03/2018 4 7 • Lump size of a material is determined by the distribution of particle sizes. • The largest diagonal size ‘a’ of a particle in mm is called the particle size. • If the largest to smallest size ratio of the particles of a lumpy material is above 2.5, they are considered to be unsized. • The average lump size of sized bulk material is 8 • Bulk weight or bulk density of a lumpy material is the weight of the material per unit volume in bulk. • Because of empty spaces within the particles in bulk materials, bulk density is always less than density of a particle of the same material. • Generally bulk load can be packed by static or dynamic loading. • The ratio of the bulk density of a packed material to its bulk density before packing is known as the packing coefficient whose value varies for different bulk materials and their lump size, from 1.05 to 1.52. Bulk density is generally expressed in kg/m^3. 25/03/2018 5 9 Angle of Repose Pile of bulk solids • Mobility not flowability of a bulk material is generally determined by its angle of repose. • When a bulk material is freely spilled over a horizontal plane, it assumes a conical heap. • The angle ‘’ of the cone with the horizontal plane is called the angle of repose. • Less is ‘’, higher is the flowability of the bulk material. • If the heap is shaken, the heap becomes flatter and the corresponding angle of repose under dynamic condition is referred to as dynamic angle of repose dyn, where dyn is generally considered to be equal to 0.7 . 10 • Classification and codification of bulk materials based on lump size, flowability, abrasiveness, bulk density and various other characteristics have been specified by a specification number • The alphanumeric codification system as per this specification is shown below: 25/03/2018 6 11 • In this material code, if any of the above characteristics is not known, corresponding number or alphabet is dropped from the material code. • Table below shows the descriptions and limits of the different classes of material characteristics. 12 25/03/2018 7 13 14 25/03/2018 8 15 • Bulk materials are generally handled by belt-conveyor, screw conveyor, pneumatic conveyor, bucket elevator, grab bucket, skip hoist, stacker-reclaimer, dumper-loader etc. • It can be handled by cranes / trucks when collected in containers or bags. • Small lump (powdered / granular) materials can be handled pneumatically or hydraulically. • Bulk materials are generally stored on ground / floor in the open or under shed, and also in bunkers / silos. 16 Vibrating Grizzly Shredder Size Control 25/03/2018 9 17 Gyratory Crusher 18 Rotary Screen 25/03/2018 10 19 Vibrating Screen 20 Based on Experience: 25/03/2018 11 21 Sieving 22 Sieve Shaker 25/03/2018 12 23 Sieves Types… Perforated Plate (round holes) Woven MeshPerforated Plate (square holes) 24 25/03/2018 13 25 Worked Example (Sieve PSD) 26 25/03/2018 14 27 28 Cumulative Distribution: Cumulative Passing (undersize) Cumulative Retained (oversize) 25/03/2018 15 29 Frequency Distribution 30 25/03/2018 16 31 32 Laser diffraction particule sizing technique • Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. • Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles, as illustrated below. 25/03/2018 17 33 Laser Diffraction MasterSizer 34 25/03/2018 18 35 36 S = Surface Area; V = Volume; Ap = Projected Area; Use consistent units 25/03/2018 19 37 Martin’s Diameter = Length of Chord through Centroid that divides Projected Area of Particle into 2 Equal Parts Feret’s Diameter = Distance between pairs of Parallel Tangents to Particle Perimeter in some Fixed Direction 38 25/03/2018 20 39 40 25/03/2018 21 41 (Base: 63.5 mm I.D.; Internal Height = 19 mm) 42 Bulk Density Plot 25/03/2018 22 43 Most Important Parameter that affects BMH Operations (basis of pricing) Also Most Difficult and Frustrating Reason: BD Variable Exacerbated by Numerous Definitions: • Loose-Poured (ρbl) • Tapped or Compacted (AS2300 Milk Powder, ISO6770 Instant Tea) • Vibrated • Fluidised • Note: Operator Dependent Bulk Density… 44 Also exacerbated by Various Measurement Techniques & Standards (ISO, AS, BS, etc Different Products) Proper Definition/Characterisation Essential Understanding Equally Important K. Truter (ICBMH’04, Wollongong) Bulk Density… 25/03/2018 23 45 Particle Density, ρs (kg/m3) 200 litre drum Gently pour in Wheat Mass of solids, Ms = 160 kg Loose-poured bulk density, ρbl = 160/0.2 = 800 kg/m3 From other Tests (pycnometer): Apparent Density of Wheat Particle: ρs = 1450 kg/m3 Solids volume = 160/1450 = 0.11 m3 Air volume = 200 – 110 = 90 litres Voidage, Γ = 1 – ρb/ρs = 0.45 46 No good for Mixtures of Particles having different ρs Also: Specific Gravity Bottle (relative density) (water displacement method) Particle Density, ρs (kg/m3) 25/03/2018 24 47 Subjective!! Only Qualitative!! Particle Shape: Flowability Packing Abrasion, etc 48 Particle Morphology Quantitative Study of Particle Shape e.g. Sphericity: Used Frequently to Define SHAPE 25/03/2018 25 49 50 25/03/2018 26 51 Flow Properties of Bulk Materials 52 Mechanical properties : Flow Properties To compare and optimize BM regarding flowability. To design BM handling equipment: silos, feeders, flow promoting devices and other bulk solid handling equipment (so that no flow problems occur e.g. flow obstructions, segregation, irregular flow, flooding,..) 25/03/2018 27 53 Designing BMH Plant – What should we know about Product(s)? An area where there is frequently a lack of attention in Design Process Handling Characteristics (FP) of Bulk Material/s Major BMH plants still being built without any good information about FP (and hence, flowability and handleability) Specifications provide scant information (e.g. mean particle size, bulk density, MC) …constants?? 54 What are Flow Properties? To design bins and associated handling systems for a bulk solid Essential access to relevant Flow Properties: Bulk density (ρ or ρb) Kinematic angle of internal friction () Static angle of internal friction (t) Effective angle of internal friction (δ) Wall friction (w) Flow Function (FF) Internal strength Cohesion and adhesion …all wrt Major consolidation stress Variations: time consolidation, MC, temp, size, etc 25/03/2018 28 55 1. Qualitative application: Flowability testing • Will the powder flow in existing equipment (e.g., dosage systems, hoppers, ...)? • Will it flow uniformly (e.g., when filling dies of tablet presses)? • Will it exhibit caking after long-term storage? • Can flowability be improved (flow agents, particle size distribution, moisture, surface characteristics, temperature ...)? • Are flowability specifications met (quality control)? 2. Quantitative application: Equipment design • Goal: To avoid flow problems with equipment by appropriate design according to flow properties 1. Why measuring flow properties? 56 Most storage and processing systems for powders are based on gravity flow. Most flow problems appear while discharging hoppers, containers, bins, silos ... To understand these flow problems, it is important to know how a powder flows …. 25/03/2018 29 57 - Mass flow (a): Entire contents is flowing downwards simultaneously. - To achieve mass flow, the hopper walls must be sufficiently smooth and steep. 58 - Funnel flow (b, c): Stagnant zones prevail on the hopper walls. - Stagnant zones may be non-symmetrical. - Sometimes funnel flow cannot be identified from the top of the silo. 25/03/2018 30 59 Stable Annular RegionCohesive Arch preventing material from exiting hopper FP needed to avoid Flow Obstructions 60 FP needed to achieve desired Flow Pattern Does not imply plug flow with equal velocity “Dead” or non-flowing region Typically need 0.75 D to 1D to enforce mass flow D Material in motion along the walls Active Flow Channel 25/03/2018 31 61 How are FP Determined? Flow properties determined experimentally Should be determined by testing representative sample of bulk material/s Generally tabulated values in codes and handbooks are NOT adequate Flow property testing can be difficult, time consuming and expensive Need to consider range of flow properties required for a particular design application 62 • FP heavily dependent on Sample(s) tested Particle size distribution Particle shape Chemical composition of particles Moisture Temperature Dangerous to extrapolate!! It is necessary to determine the flow properties in appropriate testing devices. 25/03/2018 32 63 Flow Properties Laboratory 64 Internal Strength, Cohesion, Wall Friction, Time Consolidation Used to establish Flow Properties or Flowability of a Bulk Material Unlike Solid Substances Bulk Materials capacity to Shear and Flow internally (without any fundamental failure or alteration of its structure) Unlike Liquids Bulk Materials capacity to support Shear Stresses while in Static Condition To determine Internal Strength Standardised Testers/Procedures, such as: AS3880-1991 Bin FP of