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1 QuickTime et un décompresseur Graphismes sont requis pour visionner cette image.

2 Dust Emission by Powders Renaud ANSART, John DODDS, Alain De RYCK Centre RAPSODEE Ecole des Mines d Albi, France

3 QuickTime et un décompresseur Graphismes sont requis pour visionner cette image. Dust Emission by Powders Renaud ANSART, John DODDS, Alain De RYCK Centre RAPSODEE, Ecole des Mines d Albi

4 Handling powders = Emission of dust Une poudre de ciment ordinaire Poudre de ciment Lafarge traité anti poussiere

5 Handling powders = Emission of dust Particles in Suspension = Product losses Risk of product contamination Health risks for operators Risk of dust explosions

6 Handling powders = Emission of dust Measures : Product design (such as granulation) Surface treatment of particles Ventilation and dust capture systems To be effective we must : Be able to measure dustiness Understand the mechanisms of dust emission

7 Many Tests for Measuring Dustiness

8 Tests for Measuring Dustiness A great variety of dustiness tests, all empirical. Many different ways of stressing a powder to produce dust. No real relation to processing conditions. Many different ways of characterising the dust produced (total wt.of dust, wt. of specific size fractions) Useful for comparing formulations, but not for designing ventilation and dust capture systems.

9 A study case of dust emission Powder falling from a silo into a container Forces in action Experimental set-up Results Perspectives

10 A study case of dust emission Powder falling from a silo into a container Forces in action Experimental set-up Results Perspectives

11 Experimental Set-up Load cells Pneumatic conveyor Silo Protection sleeve Particle Image Velocimetry (PIV) equipment Measuring chamber Spraytec Open path Laser diffraction PSA instrument

12 Dantec PIV System QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image.

13 Malvern Spraytec Instrument Non intrusive, in-situ, real time PSA by Mie diffraction Particle size range: 0.5 μm - 2mm Beam length 50 Cm Beam width was reduced 10mm 6mm

14 A study case of dust emission Powder falling from a silo into a container Forces in action Experimental set-up Results Particle motion Particle flow rate Particle size distribution Perspectives

15 A stream of particles falling from the silo The stream first retracts before expanding Non expansion zone near the outlet (velocity close to that of free fall).

16 Velocity vector field (PIV) Gel de Silice-Qm=1,5 g/s-h=50cm V QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. Higher velocity at centre. Particle stream grows wider with height of fall.

17 Vertical velocity of the particles Gel de Silice-Qm=1,5 g/s D=10mm Gaussian velocity profile. The stream grows wider as it falls.

18 Particle velocity at stream centre (Vmax) Silica gel 1,5 g/s D 0 =10mm PIV results Free fall velocity Velocity stabilises after a certain height of fall

19 Horizontal velocity of the particles Normalized w.r.t. max velocity Silica gel 0,6 g/s Particles move towards the edge of the stream. The speed of migration lessens with height of fall.

20 Changes in PSD with height of fall Silica gel 1,5 g/s 34,3% Mastersizer ,5bar Monomodal D10= 34 μm D50= 59 μm D90= 97 μm 14,5% The fines migrate to the edge of the stream.

21 A study case of dust emission Powder falling from a silo into a container Forces in action Experimental set-up Results Perspectives Modelling

22 Numerical modelling Liu s two phase model (negative buoyancy plume) Input parameters: Mass flow rate, particle size, density, outlet diameter Arbitrary choice of the rate of expansion of the stream α= V induced air V z(stream ) = V e V max V e V e V max Allows calculating : : Particle velocity (solid phase), Air velocity (gas phase), Flow of air induced into the stream of particles.

23 Velocity profile of the stream of particles and the entrainment factor α Width at V max /2 Here slope 6% for Liu s model Origin slightly below silo outlet

24 Model results for velocity at centre (Vmax( Vmax) Gel de Silice-Qm=1,5 g/s Good agreement between measurements and predictions for α=6,2%.

25 Velocity profile of the stream of particles and the entrainment factor α Silica gel µm Silica gel µm QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. α seems to depend on powder characteristics Could give a way to characterise dustiness

26 Perspectives Experiments underway with different powders. (particle size, density, cohesion, fines content..) Tests on anti-dust treatments for powders Tests on inserts and air injection/extraction to minimise dust emission Development of more rigorous characterisation methods for the dustiness of powders With the Fluid Mechanics Institute of Toulouse (IMFT), development of a new two phase model of particle stream to eliminate the need for parameter α.

27 Thank you for listening This research programme is financed by the CNRS, EMAC and the Institut National de Recherche et Securité (INRS)

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29 Tests for Measuring Dustiness Single drop column tests Single drop chamber tests Fluidisation tests Rotating drum tests

30 An example of a palliative mesure

31 A study case of dust emission Powder falling from a silo into a container Forces acting on a particle: gravity. bouyancy (negligeable in air). drag. Parameters of the stream: height of fall. mass flow rate. particle size and distribution. air induced in the flow. cohesion. humidity

32 Experimental Set-up Equipment Pneumatic conveyor (Gerike( Gerike) Silo 20 litre Measuring chamber 250 l QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. Instrumentation Powder flow rate by load cells Air flow into measuring chamber PIV for particle trajectories Laser diffraction for PSA

33 Tests for Measuring Dustiness Single drop column tests: example PALAS apparatus Drop powder sample down tube Measure changes in light transmission

34 Tests for Measuring Dustiness Single drop chamber tests: example Material Research Institute (MRI) apparatus Rotate and vibrate beaker to pour powder in the chamber Inlet air flow of 10 l/min Collect dust in stages of an impactor with additional air flow

35 Tests for Measuring Dustiness Fluidisation tests example : HSE fluidisation test using inert particles Fluidisation of cohesive particles in a bed of inert sand particles High stress dispersion Measurement of particle concentration above bed by collection and micro-balance

36 Tests for Measuring Dustiness Rotating drum tests example : Heubach rotating drum test 20 g powder sample put in a rotating drum with lifters Air flow carries dust to impactor for particle size and concentration measurement

37 Handling powders = Emission of dust Particles in suspension Product losses Health risks for operators Risk of dust explosions

38 Visualisations du jet Image instantanée Moy. de 500 instantanées moy 500 images QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. h = 50cm, 10x10 cm h = 50cm, 10x10 cm

39 Visualisation at silo outlet The stream first retracts before expanding Non expansion zone near the outlet (velocity close to that of free f fall).

40 Experimental results for stream expansion Silica gel Qm=1,5 g/s D orifice = 10 mm width=vmax/2 Slope=6% Validates Liu s s model Gives a value of α The origin of the linear section is below the silo outlet (initial ial retraction)

41 Plan Forces in action Experimental set-up Results Particle motion Particle flow rate Particle size distribution Perspectives

42 Plan Forces in action Experimental set-up Results Particle motion Particle flow rate Particle size distribution Perspectives

43 Handling powders = Emission of dust QuickTime et un décompresseur TIFF (non compressé) sont requis pour visionner cette image. QuickTime et un décompresseur Cinepak sont requis pour visionner cette image. Test with two different powders powder A > 100 µm powder B < 100 µm

44 Velocity profile of the stream of particles and the entrainment factor α V max α = Ve/Vmax

45 d dz π 2 ( r av a)= 2π r a v α a Q d d dz m v dz a p = 1 v p * B k ( ρ π r a v a)= k 1 Numerical modelling Liu s two phase model (negative buoyancy plume) ( ) 4/3 s v p v a ( ) 4/3 s v p v a Input parameters: Mass flow rate, particle size, density, outlet diameter Arbitrary choice of the rate of expansion of the stream i.e. α = V(induced air)/vz(stream) Allows calculating : : Particle velocity (solid phase), Air velocity (gas phase), Flow of air induced into the stream of particles. C C 1 p v Mass balance. Momentum balance (particles) Momentum balance (air)

46 Handling powders = Emission of dust QuickTime et un décompresseur TIFF (non compressé) sont requis pour visionner cette image. QuickTime et un décompresseur Cinepak sont requis pour visionner cette image. Test with two different powders (BASF) powder A > 100 µm powder B < 100 µm

47 Visualisation of the particle stream Silo outlet 30x30 cm Instantaneous image Mean of 500 instants QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. mean 500 images h = 50cm, 10x10 cm h = 50cm, 10x10 cm 2 zones : core + powder boundary layer. Mixing zone : Kelvin-Helmholtz instability.

48 Concentration profile by masking and weighing Gel de Silice-Qm=15 g/s-y/do=53.5

49 Particle size distribution of the Silica Gel Mastersizer 2000: dispersion 0,5bar Monomodal distribution D 10 = 34 μm D 50 = 59 μm D 90 = 97 μm ρ apparent = 500 kg/m3 ρ solid = 1000 kg/m3

50 Experimental Set-up Equipment Pneumatic conveyor (Gerike( Gerike) Silo 20 litre Measuring chamber 250 l QuickTime et un décompresseur TIFF (LZW) sont requis pour visionner cette image. Different size entry disks to receiving vessel

51 Concentration profile by masking and weighing Gel de Silice-Qm=15 g/s-y/do=53.5 High concentration at the centre

52 Concentration of particles in the stream Gel de Silice-Qm=15 g/s D0=20mm The porosity of the stream increases with height of fall. The particle concentration becomes more homogeneous with height of fall.

53 Concentration profile by Spraytec Laser beam Silica gel-qm=1,5 g/s Gaussian concentration,profile. Not absolute values, pb: : assume uniform concentration over beam length

54 To conclude on the experimental results Characterisation of a stream of falling particles : Particle velocity and, Width of the stream, Concentration profile of the stream, Particle size profile in the stream.