This paper describe how to reduce powder deposition

Walmsley, Timothy Gordon

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Research Commons@Waikato

Reducing Undesirable Powder DepositionTimothy Walmsley – B.E.(Hons) Ma.P.E.Supervisor: Michael Walmsley2011Commonly affected processes and industries Atomisation / spray drying◦ Food / metal / ceramics / pharmaceutical powder industries Boilers & furnaces ◦ Many industries Etc.Negative impactsProduct yield / capacityBrowning & oxidation / powder combustionPlant shut-down & cleaningHeat recovery opportunitiesEnergy ↔ $$$Traditional methodologyIdentify problemsLab testing • Temperature & relative humidity (RH)Sticky curve modelsDryer settings controlProcess Improvement:• Cyclones • Fluidised beds• Insulation• Hammers  Optimal process controlSmart processing equipment designResearch methodologyComputerModelsIn-plant observationsLab tests and model verificationFundamental understanding mechanismsExperimental & theoretical equationsIn-plant observations Hatches located in same position, but on different cyclonesLab tests – Impingement jet 0% 10% 20% 30% 40% 50% 60% 70% 80% 90%Air relative humidity (Water activity)020406080100Air temperture (°C)Critical sticky regionNon-critical sticky regionImpingement jet deposition morphologiesIncreasing particle stickinessUnderlying mechanismsStickiness - adhesion• Viscosity (T & RH)• Glass transition temp. • Surface tension• Surface energy & wetting angles (wall properties) Kinetics• Mass (size & shape)• Impact velocity• Impact angle• Air flow patternsExperimental & theoretical equationsircadinrn RVVmAUVRV tan,tan,2,2,   and  22,23inpad VdkUDeposition criteria:Rebound calculation:Computational Fluid Dynamics (CFD)Computer modelsVerification of airflow models Particle Image Velocimetry (PIV)NormalisedVelocity (V/Vmax) > 0.9  < 0.9  < 0.7  < 0.5  < 0.3  < 0.1 -30 -20 -10 0 10 20 30Distance from jet centre (mm)051015202530354045Dist ance fr om wa ll (mm)CFD PIVVerification of models Experimental morphologies-80 -60 -40 -20 0 20 40 60 80X (mm)-60-40-200204060Y (mm)-80 -60 -40 -20 0 20 40 60 80X (mm)-60-40-200204060Y (mm)Verification of models Experimental morphologies-80 -60 -40 -20 0 20 40 60 80X (mm)-60-40-200204060Y (mm)Verification of models Experimental morphologiesBend geometryThe next steps… Continue in-plant work & lab tests Improve computer model accuracy Verify results for complex geometry Apply models to industrySummary Powder deposition is costly to industry Traditional control is simple, but not optimal Verified computer models can help minimise deposition problemsNormalisedVelocityMagnitude(ms-1) > 0.9  < 0.9  < 0.7  < 0.5  < 0.3  < 0.1 -30 -20 -10 0 10 20 30Distance to impingement centre (mm)051015202530354045Normal distance to plate (mm)NormalisedVelocity Magnitude(ms-1) > 0.9  < 0.9  < 0.7  < 0.5  < 0.3  < 0.1 -30 -20 -10 0 10 20 30Distance to impingement centre (mm)051015202530354045Normal distance to plate (mm)NormalisedVelocityMagnitude(ms-1) > 0.9  < 0.9  < 0.7  < 0.5  < 0.3  < 0.1 -40 -30 -20 -10 0 10 20Distance to impingement centre (mm)051015202530354045Normal distance to plate (mm) > 0.9  < 0.9  < 0.7  < 0.5  < 0.3  < 0.1 -40 -30 -20 -10 0 10Distance to impingement centre (mm)051015202530354045Normal distance to plate (mm)Normalised velocity magnitude (ms-1) > 0.9,  < 0.9,  < 0.7,  < 0.5,  < 0.3 ,  < 0.1 -40 -30 -20 -10 0 10 20Distance to impingement centre (mm)051015202530354045Normal distance to plate (mm)

Reducing Undesirable Powder Deposition

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