Presentation on theme: "Sharon Nowak K-Tron Global Business Development Manager,"— Presentation transcript:
1Section II Bulk Material Basics and Their Influence on Equipment Selection Sharon NowakK-TronGlobal Business Development Manager,Food and Pharmaceuticals
2Agenda Session I - Corporate Introduction Session II - Bulk Materials Basics (K-Tron)Session III - Pneumatic Conveying Technology and Product Overview (K-Tron)Session IV – Feeding Technology and Product Overview (K-Tron)Session V – Advances in Twin Screw Compounding (Coperion)Session VI (Coperion)Session A: Food Extrusion on Twin Screw ExtrudersSession B: New Developments in the Compounding of PlasticsSession VII (K-Tron)Session A: Selecting the Right Feeder for Food/PharmaceuticalsSession B: Selecting the Right Feeder for PlasticsSession VIII Pneumatic Conveying (K-Tron)Session A: Pneumatic Conveying Systems for Food/PharmaceuticalsSession B: Pneumatic Conveying Systems for Plastics
3Bulk Solids Definition Moist, sticky materialsFriable materialsLarge particlesAbrasive materialsHazardous materialsBlends or MasterbatchContamination Sensitive ProductsNon-Free Flowing productsFree-flowing materialsMaterials that Fluidize or liquefyProducts that pack, plug, cake or smear
4Where do they come from? Organic Inorganic Cocoa Powder Flours Sugar Calcium carbonateTitanium dioxideSilica
5Flowability Influencers Physical & chemical propertiesMaterial CharacteristicsWith particles, equipment & environmentParticle InteractionsCompressibility & cohesionBulk PropertiesThroughput & velocityFlow RateGeometry & surface finishHandling EquipmentFlowability is not a natural material property of a particular product but being a multidimensional problem, not single set of test can determine it. Flowability is a combination of the physical properties of materials, environmental factors, processing techniques used for that material’s production, and storage equipment used to store and handle that material (Prescott and Barnum, 2000). Some key factors that influence flowability are moisture, humidity, temperature, pressure, fat, particle size and shape and addition of flow agentsPowder flowability is defined as the ease with which a powder will flow for a specified set of conditions.Powder is generally defines as a collection of individual solid particles surrounded by gas phases. This includes granular materials, bulk solids, pelletized materials, etc.Mohr-Coulomb Model is a model that can be used to accurately predict flow behavior. This model quantifies two measurable parameters: cohesion and angle of internal friction and two derived parameters: Unconfined Yield Strength and Major Consolidation StressIt is not possible to determine theoretically the flow behavior of bulk solids in dependence of all of these parametersThe flowability of a bulk solid depends on the adhesive forces between individual particles. Different mechanisms create adhesive forces such as van der Waals forces for fine-grained, dry bulk solids; liquid bridges between moist bulk solids particles.
6Material Characteristics & Tests Property MeasuredAffects…Bulk Density Loose & Compactρ = Weight per unit of volumeStorage vessels size & material’s compressibilityParticle ShapeParticle geometryDischarge from hoppersParticle Size & PSDAspect ratio (L/D)Flowability & CompressibilityParticle HardnessScratch-ability, hardness, abrasionAbrasiveness on equipment.Type of metal and surface treatment used for pipes, bins, hoppers, screws.Particle fragility.Moisture Content% of water in the materialCohesive strength & arching ability of bulk materialsPermeabilityAbility of the air to pass through bulk materialAbility to floodCompressibilitySensitivity of the material to pressureTendency to pack in a feeder hopperCohesivenessTendency of material to adhere to itselfMinimum outlet diameter for bins, hoppers, and outletsThe compacted BD could be used to determine the space used in a storage vessel once the material has time to settle, weight of the material coming from a vibrating discharge or screw conveyor or just providing one end of the weight range to aid in judgment decisions when converting volume to kilograms.
7Material Characteristics which contribute to poor flowability High Aspect RatioCompressibility and CohesivenessWide PS & PSD
8Bulk Densities Comparison 10%10%Compacted(CBD)Loose(LBD)Aerated(ABD)While were on the subject of Bulk Density - One bulk density value, we don’t have a test for, is Aerated or fluidized BD. This comes into play on materials which have a long air retention time.A rule-of-thumb method that can be used, (not real accurate), is to decrease the loose BD weight by the same percentage it was increased to calculate the compacted BD. This only applies to (C) and maybe some (B) class materials that have the ability to retain air when fluidized.As the diagram shows, if material compacts by a certain %, it usually will expand that amount when aerated.
9Loose Bulk Density (LBD) Mass per volume of “loose” powder, gm/cm3In Carr series of measurements, a sieve with a mesh size greater than D100 of sample is used to control the flow of the material being analyzed.100 CCSieveFunnelSampleSlide courtesy of Hosokawa Micron Powder Systems, Summit, NJ
10Packed or Compacted Bulk Density (CBD) Mass per volume of “packed” powder, gm/cm3.In Carr Series of measurements , fill container to top of retainer wall, typically the same size as the cup.Tapping Unit raises and drops container automatically.100 CCSieveFunnelRetainerSampleCarr Standard: 18 mm 180 tapsTapping UnitSlide courtesy of Hosokawa Micron Powder Systems, Summit, NJ
11Bulk Density Affects…The Aerolock™ is like a revolving door that moves people from one space to another. To know how many kilograms it moves per revolution, (assuming 1 body in each of the 6 pockets), the weight of each person must be known.In our case, we want to know which Aerolock™ size is needed to provide the required kilograms per hour. The volume of each pocket on an airlock is known or can be calculated and depending on style a fixed number of pockets per rotor. By using the Bulk Density information we can determine approximately how many kilograms of material it will move in one revolution.Other factors need to be considered in making these calculations, such as, how fluidizable is the material, how well does it retain air, will it flow easy enough to provide full pocket fill, etc.The compacted BD could be used, for example, to determine the space used in a storage vessel once the material has time to settle. Weight of the material coming from a vibrating discharge or screw conveyor. Or just providing one end of the weight range to aid in judgment decisions when converting volume to kilograms.Bear in mind that during different stages of conveying, bulk density may vary from LBD to Aerated BD
12Inorganic: Bulk Density of Calcium Carbonate CaCO3 (95% pure)CaCO3 (99% pure)LBD 1.38 g/cm3CBD g/cm3LBD 0.3 g/cm3CBD 0.4 g/cm3
13Organic: Bulk Density of Sugars LBD g/cm3CBD 1.06 g/cm3LBD g/cm3CBD .95 g/cm3
14Particle Shape Aspect Ratio Circular Sugar Cube CaCO3 Feldspar Pellets ResinWoodBlockSiO2BaSO4PlateletsMicaTalcFiberGlassWollastoniteAPI’sFibersIncrease tensile strength and stiffnessDecrease 3D shrinkagePlateletsIncrease stiffnessDecrease tensile strength, impact strength and 3D shrinkageSpheresIncrease stiffness (medium), impact strength (PE, PPH)Decrease tensile strength, 3D shrinkageParticle shape can give some insight into how the material may react in hopper discharging, feed through Aerolocks, potential bridging, etc. However, there is no test to determine particle shape. Under the Visual Observation section, one describes additional comments pertaining to the shape or unusual characteristics describing the material.Aspect Ratio
15Sample Sieve Analysis of Powdered Sugar The additional indicators, shown in the NOTE column, describe material conditions on a screen, indicating some of the particles on this sieve are smaller than the screen openingsBL (blinding): When multiple particles form a bridge over the screen openings.Particles by themselves are less than screen size.BA (balling): Indicates the material, during the Ro-Tap operation, formed large agglomerates made up of individual particles which were smaller than the screen openings.Each sieve that carries any one of these indicators will cause the material factor number to decrease by one. The “Material Factor” value is determined by the material Size Code and the percent of material passing the 230 sieve.This value is used to determine air / cloth ratios needed in destination filters.For example, the sieve analysis of a “C” class material, indicated above, the material factor would normally be 8. Since three sieves are marked as balling and/or blinding, the actual material factor would be 5.Point out agglomerates are made up of finer material which is difficult to filter.The reasoning behind this, if material doesn’t shake through these sieves for any reason other than particle size, the percent passing is not a true reflection of the sample particle distribution.This could result in sizing a smaller filter than required for this material.There has been some discussion as to the validity in this process, on the premise that if the material particles bind together they should be easier to filter out. On the other hand, if the material bonds together during the sieve testing, will it also do the same in the conveying air stream?This is a decision we have to make when sizing filters.
16Particle Size Code A Code C Code B If the majority of the material is above the #35 sieve, and particles uniform in shape (code A material).If the majority of the material is below the #60 sieve, it’s (code C material).Everything else is (code B material).Code CCode B
17Particle Size & PSD Sieve Number % Passing Particle Size (mm) 1/431/25102030406080100100Top Cut90807060% Passingd505040Broad DistributionALL PARTICLES HAVE AN EFFECT ON MECHANICAL PROPERTIESTOP CUT = PARTICLE SIZE AT 98%- a measure of the coarser particlesCOARSE ARE STRESS CONCENTRATORS- can limit impact strength- higher Wear & AbrasionFINES AFFECT RHEOLOGY & SURFACE FINISHhigh fines give high surface areaSPECIFIC SURFACE AREAHigh value will reduce compounding efficiency3020Narrow Distribution101086422.214.171.124.20.1Particle Size (mm)
18Particle Hardness TiO2 CaCO3 Kaolin Talc SiO2 6-7 3-4 4-8 1 – 1.5 Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds.However the behavior of solid materials under force is complex, therefore there are different measurements of hardness: scratch hardness, indentation hardness and rebound hardnessMohs hardness is defined by how well a substance will resist scratching by another substance. It is rough measure of the resistance of a smooth surface to scratching or abrasion, expressed in terms of a scale devised (1812) by the German mineralogist Friedrich Mohs. The Mohs hardness of a mineral is determined by observing whether its surface is scratched by a substance of known or defined hardness.To give numerical values to this physical property, minerals are ranked along the Mohs scale, which is composed of 10 minerals that have been given arbitrary hardness values. The minerals contained in the scale are shown in the Table; also shown are other materials that approximate the hardness of some of the minerals. As is indicated by the ranking in the scale, if a mineral is scratched by orthoclase but not by apatite, its Mohs hardness is between 5 and 6.In the determination procedure it is necessary to be certain that a scratch is actually made and not just a "chalk" mark that will rub off. If the species being tested is fine-grained, friable, or pulverulent, the test may only loosen grains without testing individual mineral surfaces; thus certain textures or aggregate forms may hinder or prevent a true hardness determination. For this reason the Mohs test, while greatly facilitating the identification of minerals in the field, is not suitable for accurately gauging the hardness of industrial materials such as steel or ceramics. (For these materials a more precise measure is to be found in the Vickers hardness or Knoop hardness;)Another disadvantage of the Mohs scale is that it is not linear; that is, each increment of one in the scale does not indicate a proportional increase in hardness. For instance, the progression from calcite to fluorite (from 3 to 4 on the Mohs scale) reflects an increase in hardness of approximately 25 percent; the progression from corundum to diamond, on the other hand (9 to 10 on the Mohs scale), reflects a hardness increase of more than 300 percent.For a full description of hardness measurement methods see:
19Hardness Methods Rockwell Brinell Vickers Knoop Shore Mohs Barcol Mineral nameHardness (Mohs)Hardness (Vickers) kg/mm2Graphite1–2VHN10=7–11Tin1½VHN10=7–9Bismuth2–2½VHN100=16–18Gold2½VHN10=30–34SilverVHN100=61–65Chalcocite2½–3VHN100=84–87CopperVHN100=77–99GalenaVHN100=79–104Sphalerite3½–4VHN100=208–224Heazlewoodite4VHN100=230–254Carrollite4½–5½VHN100=507–586Goethite5–5½VHN100=667Hematite5–6VHN100=1,000–1,100Chromite5½VHN100=1,278–1,456Anatase5½–6VHN100=616–698Rutile6–6½VHN100=894–974PyriteVHN100=1,505–1,520Bowieite7VHN100=858–1,288Euclase7½VHN100=1,310Chromium8½VHN100=1,875–2,000RockwellBrinellVickersKnoopShoreMohsBarcolCommon Abrasive MaterialsSandQuartzPVC CompoundGravelGlassClay and MineralsSugarSteelNylon/Glass-Filled Pellets
20Particle Interactions… Particle – ParticleVan de Waals ForcesElectrostatic ForcesCapillary ForcesSintering ForcesCollisionsParticle – EquipmentFrictionShear StrengthParticle – EnvironmentHumidityTemperaturePermeabilityVibrationTimeThree distinctive relationships affect the flow behavior of mineral fillers in pneumatic conveying and feeding systems: Particle-particle, particle-equipment and particle-environment interactions.Particle-ParticleParticle-particle interactions are directly related to the filler’s chemical composition and physical characteristics rather than bulk properties. The most important particle-particle forces are the electrostatic or van der Waals forces of attraction between molecules. As the separation between particles increases, the van der Waals forces decrease, explaining why the addition of small particles to cohesive powders improves their flowability. Other particle-particle forces include capillary forces, responsible for liquid bridge formation, and sintering forces, responsible for solid bridge formation. Capillary forces develop in the presence of water vapor in the gas phase whereas sintering forces develop when material migrates due to diffusion or viscous flow. Interparticle forces contribute to the cohesive characteristics of fine powders and their tendency to form aggregates or agglomerates.Particle-EquipmentThe flow of solid particles inside a vessel or a pipe is a function of two important characteristics, wall friction and shear strength. Wall friction relates to how particles slip on a contact surface while shear strength is the resistance that the powder bulk offers to deformation, or how particles slip relative to each other.Particle-EnvironmentParticle-environment interactions deal with external forces (e.g., temperature, relative humidity, vibration, gravity, aeration, etc.) exerted over the aggregate of particles. The air Relative Humidity (RH) and the filler’s hygroscopic nature are often coupled with increase cohesiveness because of inter-particle liquid bridges; temperature affects the particle’s crystallinity behavior, promoting “caking”, while pressure increases the contact points between particles, causing “compaction” or more inter-particle adhesion.
21Moisture Content Increase cohesiveness Inter-particle liquid bridge formationSubstantial effect on frictional properties of materialsThe moisture in a bulk material is presumed to be solely water which can be evaporated by drying. Other fluids besides water such as vegetable oils and cutting oils may wet bulk materials and, if present, should be specifically described in addition to the water moisture and the amounts indicated in an easily understood mannerMoisture in bulk materials may be present in several forms:(a) Absorbed water is that water which is mechanically held in a bulk material usually in the voids between particles, and having physical properties not substantially different from ordinary water at the same temperature and pressure.(b) Adsorbed water is that water which is held by physiochemical forces, usually as films surrounding the individual particles, and has physical properties substantially different from absorbed water or chemically bound water at the same temperature and pressure.(c) Chemically bound water may be subdivided into:(1) Water of Formation is water that is actually included in the molecular structure of the compound. A decrease in moisture changes the chemical composition and may change the handling properties of the material.(2) Water of Crystallization, or Hydration, is water held to the molecule by a loose chemical bond. A change in moisture does not change the chemical composition but may change the handling properties of the material.When considering the moisture in bulk materials containing or composed of water soluble salts, it must be understood that this moisture is present as a saturated solution of the soluble salt. Such solutions may have properties much more deleterious to the maintenance of conveyors than ordinary water.
22Particle – Particle Interactions Capillary ForcesSintering ProcessFor two spherical particles in the pendular state, the maximum static liquid bridge or capillary force is given by Fc = 2πRγwhere γ is the surface tension of the liquid. Once again, the capillary force calculated for water using the particle radius R is much greater than the weight of the particle in the fine particle size range (<100 μm), and it is more realistic to use the size of the asperitiesSintering is a time-dependent process where material migrates due to a number of different mechanisms such as volume diffusion, surface diffusion, viscous flow or evaporation/condensation to the region of contact between two particles to form a neck. The size of the neck ε, relative to the particle radius R, increases with time t, according to the equationLiquid Bridges!Solid Bridges!Fc = 2πRγε n = ktR
23Particle – Particle Interactions van der Waals ForcesFνω = AR / 12a2Fνω = hŵ hŵ__8πa πa2HMESSAGE: Van der Waals forces are independent of particle radius RMESSAGE: Interparticle forces depend more on the particle surface properties than on the bulkThe dominant interaction forces between particles in a dry powder are the electrostatic or van der Waals forces of attraction between molecules. Both Hamaker and Lifshitz quantified the van der Waals attraction forces for macroscopic bodies such as two spherical particles, and these are given by Eqs. 1 and 2, respectivelywhere A is Hamakers constant, h$ is the Lifshitz-van der Waals constant (values for most solids in air range from 1 to 10 eV), H is the hardness of the softer of the materials in contact, a is the surface separation which is of the order of the intermolecular spacing (0.165 to 0.4 nm) and R is the radius of the spherical particle. For materials with hardness above 105dynes/cm2, the second term in Eq. 2 can be neglected and the two equations become identical with A = 3hŵ/4π.Using either Eq. 1 or 2, we find that the van der Waals force is of the same order of magnitude as the gravitational force for particles as large as 1 mm; yet these large particles are not cohesive, are free flowing and can be easily fluidized in a conventional fluidized bed. Thus it is apparent that the interparticle forces depend more on the particles surface properties than on the bulk, and a number of researchers have concluded that a measure of the particles surface asperities (usually taken as 0.1μm) should be used instead of the particles radius R in Eqs. 1 or 2.Fνω =1 to 10eV (most solids)Gravity Defiance!
24Particle – Equipment Interaction FrictionInternalSolid particles flowing against each otherAngle of internal frictionWallSolid particles sliding along a surfaceWall friction angleFRσAζAV = KΔФA
25Particle – Equipment Interactions After operating for a while the filter bags become caked with dust.Accumulated dust reduces air flow and conveyance efficiency.Most dust collectors have automatic bag cleaning to shake or blow the dust down to the bottom binThe operation of the bag cleaning feature produces a dust cloud within the dust collector.If burning material is present or introduced into the dust collector during the operation of the bag or filter element cleaning cycle a deflagration can result from
27Particle – Environment Interactions Time ConsolidationIncrease in strength when stored at rest under compressive stress for a long time intervalSinteringPlastic deformation at particle contactsInteractive Forces!σvAσcATemperatureSome materials are sensitive to the temperature at which they are handled or stored. A solid's temperature environment can affect its cohesiveness. For example, many chemicals and plastic powders become more difficult to handle as their temperature rises. These type materials soften or form stronger cohesive bonds as their temperature increases. Usually increases in temperature are troublesome; however, freezing temperatures can cause the individual particles of materials like coal, sand, etc. to freeze together forming very strong bonds.Some materials exhibit more strength at constant temperature, while others gain cohesive strength as the temperature changes during heating or cooling. An example of this phenomenon is soybean meal. If soybean meal is stored at temperatures of 90 °. Or less, it is usually not difficult flowing material.If, however, the soybean meal is allowed to heat to 100 ° or greater (such as during summertime conditions), it behaves completely different. At 100 ° or greater, soybean meal becomes extremely cohesive and capable of bridging or arching over very large openings.TimeStorage at rest is responsible for many of our industries flow problems.Many materials are free flowing if handled in a continuous fashion. In other words, as the material is placed in a storage vessel, it is immediately discharged and not allowed to remain stagnant for extended periods of time. Unfortunately, it is not practical to design storage vessels for only continuous flow conditions.Most solids are required to be stored at rest for some period of time.Large silos are expected to store quantities of material at rest for some time, to be supplied to trucks, processes, etc. Whether they are stored just overnight or for a weekend, most solids are sensitive to time of storage at rest. Cohesive bonds become stronger as the materials remain stagnant. In time, some solids can gain tremendous strength which leads to bridging or ratholing over even very large outlets
28Stresses in Bulk Solids Not a Newtonian Fluid!Shear stresses can be transmitted even at restShear stresses are different in different cutting planesState of stress in a bulk solid cannot be completely described by a single numerical valueCompressibilityCohesionZσzzζzyζzxζ yzζ xzσ yydzζxyσxxζyxIf the bulk solid were to behave like a Newtonian fluid, the stresses in all directions would be of equal magnitude.Within the bulk solid the horizontal stress is a result of the vertical stressYdxdyXσ = Stressζ = Shear
29PermeabilityAbility of gas to pass through the material
30Gas PermeabilityA measure of how easily gas flows through standing materialRelates to particle size, shape, and densityWhy is important?Tendency for the bulk material to fluidize or “flood”Pellets have high gas permeability and thus don’t easily floodFine fumed silica has poor gas permeability thus will flood easily as the sub-micron, light weight particles become entrained in the air stream
31CompressibilityThe ability of the powder to be compressed within a specified container(NOTE: Carr used a 100 cc containerThe value is determined by calculating subtracting the Aerated from the Packed Bulk Density Measurements.100 x( Packed - Aerated )Packed Bulk Density= % CompressibilitySlide courtesy of Hosokawa Micron Powder Systems, Summit, NJ
32Additional Laboratory Tests Angle of ReposePoured AngleAngle of SpatulaCan VelocityTerminal VelocityBulk VelocityFluidizabilityAnd these are determine by a series of laboratory tests. For instance, Bulk Density is determined according to ASTM #C29-60Flow angles such as angle of external friction, angle of internal friction, angle of repose (loose), and angle of slide are calculated according to CEMA standard 550.Sieve Analysis is calculated according to ASTM #C136 Standard Method of Test for Sieve Analysis of Fine and Coarse Aggregates using a Tyler Ro-Tap machine or equal. The standard specification for these screens or sieves is ASTM E11. For very fine materials or when the grain size distribution of the material passing the No. 200 sieve is of interest, the “Method of Test for Materials Finer than No. 200 Sieve in Mineral Aggregates by Washing” ASTM C117 may be used.With the exception of Abrasion, Fluidizability and Moisture content, we don’t have tests to determine the different characteristics of the material. They are indicated based on visual observation of the person conducting the test. Some of the characteristics we look for while handling the material are;Does it stick to utensils? (Adhesive)Does it form lumps, when compressed, which do not easily fall apart? (Cohesive)Does it contain fine particles that have a tendency to float in the air when disturbed? (Dusty)Does it contain long strands or stringy particles? (Fibrous)Is it extremely light weight, easily moved by mild air disturbance? (Fluffy)Does it have a tendency to grow larger particles because of particle surface attraction? (Mats & Agglomerates)Do individual particles interlock together and not easily separate? (Interlocks)Does it seem to absorb moisture from the air or your hands during testing (Hygroscopic) Sometimes found on MSDSDoes the material feel wet or oily? (Moist/Oily). We have a moisture test unit which will measure percent of moisture by weightAre the material particles easily broken or altered from their original state during handling? (Degradable)Does it have a tendency for different particle sizes to separate during handling, especially while performing angles testing? (Segregates)During terminal & bulk velocity testing, does it coat the test lines, other than static cling? (Blinds Test Tube)Does it have any irritating characteristics as to personnel handling (Irritant)Conveyor Equipment Manufacturers Association Guidelines CEMA Standard 550, March 26, 2009
33Angle of Repose Sugar Cycloserine PE pellets Shredded PS Angle of Repose is the angle to the horizontal that a bulk solids makes as it flows, unconstrained onto a flat, level surface.It is an indication of the friction exerted between material particles.PE pelletsShredded PS
34Angle of Repose (loose) Added Height58 cm.4 cu.m.2 cu.m.2 cu.m.Intro here picture of pileWith angle of reposeConvert all these to metric26 cu.m.22 cu.m.4.5 m.3.9 m.3 m. Dia.3 m. Dia.This is the angle to the horizontal that a material makes as it drops unconstrained onto a flat, level surface.The volume of the first silo is 1000 cu. ft., when I tried to put the material in it 151 cu. ft. wouldn't fit.Angle of repose closed the inlet !The additional height on the second silo takes care of this.I need a flat bottom, closed top silo that will hold 28 cubic meters of material. If I design the volume of the vessel to exactly match the requirements, I’m in trouble, unless the material is liquid. Additional height needs to be added to the hopper to accommodate this cone of material which formed during the filling process.The shaded area in the sketch represents the required 28 cubic meters of material.The angle of repose also used in determining where to place level controls, both side and top mounted switches.Water Fill Volume of this bin28 cu. m.Water Fill Volume of this bin33 cu. m.
35Can Velocity –the gas velocity within a specific area Can Vel = CFM/ABHCFM = Gas volumeABH = Cross sectional area (of receiver housing, bag house, etc)Interstitial Velocity – The apparent velocity of a gas as it passes by a filter bag matrix.It is found by dividing the collector gas volume by its cross sectional area, after the cross sectional of the bags have been subtracted from the collector cross sectional area.Movie (Can Velocity) (Auto start)FinishedClick
36Can VelocityBelow 100 FPMWe’re talking about the air velocity flowing up through a filter housing, especially filter receivers. The can velocity is set to limit the air speed inside the vessel to lift 10% or less of the conveyed material up into the filter area. When calculating can area, one needs to subtract the area taken up by the filters.The light orange shaded area is calculated by normal interpolation between the tested values, and rounded down to the nearest 5 fpm., velocity that coincides with 10%. As for the dark orange shaded area (below 100 fpm), can velocity is determined solely by interpolation between zero and the 100 fpm measurement.Explain potential errors in interpolations.
37Kinematic Angle of Surface Friction Pressure or ForceF┴F║’Particle to Wall FrictionKinematic Angle of Friction
38Placement of low level indicator. Loose Drained AngleCalculate the volume of the inverted cone created during discharge.Determine silo effective usable space, from low level signalDetermine where the low level indicator should be locatedUsable refill area.Placement of low level indicator.This angle is like the upside down version of the poured angle.This information can be useful in making decisions on whether flow aids are needed for proper discharging. (The steeper the angle the more difficult to discharge).
39Four Basic Categories of Flow Types FloodableWhen mixed with air/gas become highly charged like a fluidDifficult to handle. Flows freelyFlows across conveyor belts and screws faster than the speedCohesiveCompressible material. Packs easilyStickyHygroscopicEasy flowingFree-flowing. Does not stick togetherUniform particle size and shapeDoes not absorb air/gas and become fluidizedDifficult flowingMaterial tends to mat together (strings)Non-uniform particle size and shapeFragileCoarse or abrasive
40Powder Tester for Flowability Over the years, in an effort to reduce human subjectivity while performing the Carr methods, instruments have gone from strictly manual to computer assisted operation.Slide courtesy of Hosokawa Micron Powder Systems, Summit, NJ
41Flowability as per the Ralph Carr series of Indices Slide courtesy of Hosokawa Micron Powder Systems, Summit, NJ41
42Floodability as per the Ralph Carr series of Indices Slide courtesy of Hosokawa Micron Powder Systems, Summit, NJ42
43Summary: General Scale of Flowability Flow CharacteristicCompressibility Index (%)Hausner RatioExcellent≤ 101.00 – 1.11Good1.12 – 1.18Fair1.19 – 1.25Passable1.26 – 1.34Poor1.35 – 1.45Very Poor1.46 – 1.59Very, very poor> 38> 1.60Source: Carr. R.L. Evaluating Flow Properties of Solids. Chem. Eng. 1965, 72, 163 – 168