Pipeline Flow of Settling Slurries Presentation to Institution of - PowerPoint PPT Presentation

Pipeline Flow of Settling Slurries Presentation to Institution of Engineers Australia (Mechanical Branch) Jeff Bremer - 23 rd April 2008

Overview and Aims 1. Explain physical laws underlying the behaviour of settling solids in slurry pipeline flow. 2. Compare theories associated with pipeline flow. Why are there so many? 3. Show where and how the theories disagree. 4. Present some preliminary results from recent work (J. Bremer, V.Lim & R.Gandhi ) ??

QUESTIONS 1. Where and why are slurry pipelines used? 2. What is a settling slurry? 3. What are the main features in pipeline flow? 4. Engineers are good at using theoretical and empirical “best fit” theories. What’s the problem? 5. What are the underlying equations and physical phenomena? 6. What are the theories of pipeline flow? 7. What do we know that is right, and can we easilly confirm that we have the “right answer”? 8. What’s the latest, and where to in future?

Slurry Pipelines Slurry pipelines are used mostly for “short haul” duties, e.g. dredging (~300m ), process plants (~300m) and tailings (~3 km) In some “long haul duties”, minerals are pumped many hundreds of kilometres. Alumbrera copper concentrate pipeline (316 km), Argentina ENGINEERED BY PSI Photo’s with permission of PSI Australia Pty. Ltd., 66 Kings Park Rd.,West Perth, WA 6005,Tel. no. (08) 9463-6606.

Slurry Pipelines Each type of duty has its own “best operation point”, where the size of the particles and the tendency to settle has a strong impact on capital and operating cost. ENGINEERED BY PSI Photo’s with permission of PSI Australia Pty. Ltd., 66 Kings Park Rd.,West Perth, WA 6005,Tel. no. (08) 9463-6606.

Settling Slurries Settling Slurries Non Settling Slurries contain particles that contain particles that will fall and settle at remain in suspension the bottom of a for a long time container SETTLING NON-SETTLING Particles > 40 µm • Particles < 40 µm Wide range of sizes from • Viscosity modified by particles Small (suspensions) 40 µm ~ 200 µm Medium (transition) 200 µm ~ 2 mm • Increasingly non-Newtonian Large (heterogeneous) 2 mm ~ 5 mm as concentration increases Very Large (hetero “ “ ) 5 mm ~ >200 mm? Transport velocity must increase as size increases

Settling Slurries SETTLING Particles > 40 µm Wide range of sizes from Small (suspensions) 40 µm ~ 200 µm Medium (transition) 200 µm ~ 2 mm Large (heterogeneous) 2 mm ~ 5 mm Very Large (hetero “ “ ) 5 mm ~ >200 mm? Transport velocity must increase as size increases

Settling Slurries SETTLING Particles > 40 µm Wide range of sizes from Small (suspensions) 40 µm ~ 200 µm Medium (transition) 200 µm ~ 2 mm Large (heterogeneous) 2 mm ~ 5 mm Very Large (hetero “ “ ) 5 mm ~ >200 mm? Dead Donkeys?

Pipeline Flow of Newtonian Liquids Δ 2 P L V H W = f = ρ g 2 D g Darcy-Weisbach equation L f H W = head loss due to friction (m) D f = friction factor (dimensionless) L = length of pipe (m) D = internal diameter of pipe (m) (m 2 /s) g = accelaration due to gravity V = mean Flow velocity (m/s) Moody Diagram H ead Loss H W 2 P v + z H 1 = 1 + 1 2 v + z ρ P g 2 g H 2 = 2 + 1 ρ g 2 g Pipe Flow C.Y. O’Connor Pipeline c.a. 1899

Features of Settling Slurry Pipeline Flow Fluidised Homogeneous Fluidised Heterogeneous Homogeneous Heterogeneous Flow Bed 1. Size does matter. Fixed Bed Flow • Larger particles require increased transport velocity • Smaller particles (particularly Hydraulic gradient, i ( m/m ) fines <40 µm) can modify viscosity. Helps to suspend larger particles . 2. Flow velocity generates turbulence which keeps V 2 V 4 V 1 V 3 =V dep particles suspended. Settling Slurry Carrier Water Mean Velocity , V (m/s) 3. The system curve has a minimum that bounds different flow / friction processes

Newitt’s Classification of Slurry Pipeline Flow Solids Concentration Newitt et al (1955) described a range of flow flow/deposition phenomena after observing sand and coal particles in 25mm Perspex pipes. His classifications are still used today. Newitt, D. M., J. F. Richardson, M. Abbott, and R. B. Turtle. 1955. Hydraulic Conveying of Solids in Horizontal Pipes. Trans. Institution of Chemical Engineers 33: 94-113.

Frictional Head loss Mechanisms Head Loss , 5mm gravel,Cv=10%, DN400 Pipe • Since we 500 understand the 450 behaviour of water (the carrier) we can 400 = + H H H calculate the M W S 350 frictional head Frictional Head Loss due to losses caused by ) r 300 e solids - H s t a Water wall friction - H W W ‐ m ( 250 s Settling o L Slurry d a e 200 H Deposition Point • The remainder must 150 be friction losses Frictional Head Loss due to wall friction of carrier fluid between 100 with pipe- H W (a) particles and fluid 50 0 (b) particles and pipe 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 wall Flow Velocity (m/s) (c) particle-particle collisions.

Durand Theory -1952 − φ = ψ 1 . 5 82 . − 1 . 5 ⎡ ⎤ − ρ 2 i i V = M W ⎢ ⎥ 82 . C ρ − ρ D ⎣ ⎦ C . i gD V W S Durand, R. 1952. The Hydraulic Transportation of Coal and Other Materials in Pipes. Colloq. of National Coal Board, London.

Durand Theory – (contd) Head Loss , 5mm gravel,Cv=10%, DN400 Pipe 500 1. Durand’s Theory is purely correlative. = + 450 H H H M W S 2. The curve fit was for 305 points, for sand 400 and coal running between 200 µm and 25 350 Frictional Head mm. Loss due to ) r 300 e solids - H s t a Water W ‐ 3. The results are in “Head of Carrier Fluid” m ( 250 s Settling o L Slurry d – usually water. a e 200 H Deposition Point 150 4. As transport velocity becomes large, the Frictional Head Loss due to wall friction of carrier fluid slurry curve converges to water head loss 100 with pipe- H W from above. 50 0 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 Flow Velocity (m/s) − 1 . 5 ⎡ ⎤ − ρ 2 i i V = “Nothing proves that such a formula is M W ⎢ ⎥ 82 . C ρ − ρ D rigorously exact. Doubtless exists a ⎣ ⎦ C . i gD V W S more accurate and more complex means of notation, but the one given − φ = ψ 1 . 5 above groups quite favourably” 8 2 . − = + ψ 1 . 5 H H ( 1 C . 82 . ) M W V

More Theories (To name a Few) Correlation 1. Durand – 1952 2. Homogeneous Mixture Theory 3. Newitt et. Al - 1955 Correlation 4. Rose and Duckworth – 1969 5. Heyden and Stelson - 1971 Correlation 6. Volcado and Charles 1972 Correlation Part theory part 7. Wasp et al - 1977 correlation 8. Lazarus – Neilson 1978 Correlation 9. Wilson - 1992 10. Wilson Addie & Clift 1997 In Current Use Not in Use

No Problem – “I’ve got a Computer” Head Loss at 6.6 m/s , 5mm gravel, Cv=10% DN400 Pipe x 1000m 800 700 Answers Using 600 commonly accepted ) 500 theories can vary by m ( s Lazarus ‐ Neilson several hundred o 400 L d percent – AND Wilson ‐ Addie ‐ Clift a e H 300 MORE! Durand 200 Water 100 0 0 2 4 6 8 10 Flow Velocity (m/s)

Settling and Drag Forces on Particles Depends on density , particle diameter, shape, Reynolds number and surface effects

Settling and Drag Forces on Particles Particles > 150 µm Drag coefficient as a function of Reynolds number for smooth spheres and cylinders (Munson et al. 2002, 582) Known correlations to correction C D based on shape effect Slip Velocity to Produce drag force F D

Settling and Drag Forces on Particles Turbulent fluctuation of particle velocity in the direction of flow

Settling and Drag Forces on Particles Head Loss , 5mm gravel,Cv=10%, DN400 Pipe 500 = + H H H M W S Solids concentration 450 approaches input − = + ψ 1 . 5 400 H H ( 1 C . 82 . ) concentration M W V 350 Hs=constant ) r Frictional Head 300 e t a Water Loss due to W ‐ m solids - H s ( 250 s H s Settling o L Slurry d a e 200 H Deposition Point Δ 2 P L V 150 H W = f = H W ρ 100 g D 2 g Frictional Head Loss due to 50 wall friction of carrier fluid with pipe- H W 0 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 Flow Velocity (m/s) • In the limit the slip velocity is roughly constant as the average velocity of particles in direction of flow equals approaches the velocity of the liquid i.e.V solid = V liquid the “homogeneous limit” . In other words Hs << Hw • In Durand Theory in the limit Hs zero

Comparison of Theories Head Loss , 5m m gravel,Cv=10% , DN 400 Pipe x 1000m 8 0 0 7 0 0 6 0 0 5 0 0 ) m ( L azarus Ne ilson s o 4 0 0 L d W ilson A ddie a e Clift H Durand 3 0 0 2 0 0 1 0 0 0 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 Flow V e locity (m /s) Location of The Deposition Velocity and Head Loss at Deposition is the Key to having an accurate Theory. Clearly the “state of the art is not good”

Comparison of Theories Head Loss, 100µm particle, Cv=10%, DN100 pipe x 1000m 500 450 400 350 ) m ( 300 s s Wilson Addie Clift o 250 l d Durand a 200 e Lazarus Neilson H 150 Water 100 50 0 0.00 2.00 4.00 6.00 8.00 10.00 Velocity m/s Agreement is less critical at 100 µm