7. Pump and pipeline characteristics

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  • 1. oe4625 Dredge Pumps and Slurry Transport Vaclav Matousek October 13, 2004 1 Dredge Pumps and Slurry Transport Vermelding onderdeel organisatie
  • 2. Part II. Operational Principles of Pump-Pipeline Systems Transporting Mixtures7. Pump and Pipeline Characteristics8. Operation Limits of a Pump-Pipeline System9. Production of Solids in a Pump-Pipeline System10. Systems with Pumps in SeriesOctober 13, 2004 2 Dredge Pumps and Slurry Transport Vermelding onderdeel organisatie
  • 3. wb3414 Dredging Processes 2October 13, 2004 3Dredge Pumps and Slurry TransportVermelding onderdeel organisatie
  • 4. 7. PUMP AND PIPELINE CHARACTERISTICS HOW TO SELECT A SLURRY PUMP H-Q CURVES FOR PUMPS AND PIPES WORKING POINTS/RANGES OF PUMP-PIPE SYSTEM October 13, 2004 4 Dredge Pumps and Slurry Transport
  • 5. HOW TO SELECT A SLURRY PUMPA pump operates at the intersection of- the pipeline H-Q curve (modified Im-Vm curve) and- the pump H-Q curve.Two separate curves must be created:- the pipeline curve, H-Q, which represents the head (H) required by the particular pipeline for various flow rates (Q) and- the pump curve, H-Q, which represents the head (H) produced by the pump at various flow rates (Q) at a certain impeller speed (rpm). October 13, 2004 5 Dredge Pumps and Slurry Transport
  • 6. HOW TO SELECT A SLURRY PUMPThe head H required by the pipeline is the head lost in the entire pipeline due to:- the friction loss: major and minor losses- the loss/gain due to the change in elevation: potential energy loss/gain.The head H produced by the (centrifugal) pump is the head (the manometric pressure) developed in the mixture flowing through the rotating impeller of the pump.The slurry pump is chosen that offers the most efficient (BEP) and safe (Vdl, NPSH) operation of a pump-pipeline system. October 13, 2004 6 Dredge Pumps and Slurry Transport
  • 7. HOW TO SELECT A SLURRY PUMPThe characteristics of the IHCslurry pump (water operation):- ∆P(H) – Q for various impeller speeds (rpm)- Efficiency – Q for various impeller speeds, the Best Efficiency Point (BEP) varies with rpm. October 13, 2004 7 Dredge Pumps and Slurry Transport
  • 8. INTERMEZZO: Conservation of Energy The Bernoulli equation: quantifies the amount of mechanical energy available at a certain location in a flow.Mechanical energy components:• the potential energy of fluid control volume per unit gravity force, expressed as the geodetic h [m] height (head) P• the flow energy (or flow work), expressed as the [m] pressure head ρf g 2• the kinetic energy, expressed as the velocity Vm [m] head 2g October 13, 2004 8 Dredge Pumps and Slurry Transport
  • 9. INTERMEZZO: Conservation of Energy 2 P Vm h+ + = Level.of .Mech.Energy ρ f g 2gOctober 13, 2004 9Dredge Pumps and Slurry Transport
  • 10. INTERMEZZO: Conservation of EnergyIncompressible, steady and frictionless flow (ideal liquid):The level of mechanical energy (H), i.e. the sum of three energy components, is constant at all locations along a pipe. 2 P V h+ + = const. m ρ f g 2gThus for two locations (1) and (2) distant from each other along a pipe 2 2 P Vm1 P2 Vm2 h1 + 1 + = h2 + + ρ f g 2g ρ f g 2g October 13, 2004 10 Dredge Pumps and Slurry Transport
  • 11. INTERMEZZO: Conservation of EnergyIncompressible, steady and viscous flow (real liquid):The level of mechanical energy (H), i.e. the sum of three energy components, drops along a pipe due to energy loss. 2 P V h+ + ≠ const. m ρ f g 2gThus for two locations (1) and (2) distant from each other along a pipe 2 2 P Vm1 P2 Vm2 h1 + 1 + = h2 + + + Hloss ρ f g 2g ρ f g 2g October 13, 2004 11 Dredge Pumps and Slurry Transport
  • 12. INTERMEZZO: Conservation of EnergyThe static-pressure (P)variation along suction anddischarge pipes connectedwith a pump (schematic).The static pressure varies due tochanges in- the geodetic height (suction pipe)- the velocity [head] (change in pipe diameter in front of the pump)and…due to the losses (both in suction anddischarge pipes). October 13, 2004 12 Dredge Pumps and Slurry Transport
  • 13. H-Q CHARACTERISTICS H-Q PUMP H-Q PIPELINE H-Q PUMP-PIPELINE SYSTEMOctober 13, 2004 13Dredge Pumps and Slurry Transport
  • 14. Hman-Q CURVE OF A CENTRIFUGAL PUMP October 13, 2004 14 Dredge Pumps and Slurry Transport
  • 15. H-Q CURVE OF A PIPELINEOctober 13, 2004 15Dredge Pumps and Slurry Transport
  • 16. H-Q CURVES OF A PUMP-PIPELINE SYSTEM October 13, 2004 16 Dredge Pumps and Slurry Transport
  • 17. Hman-Q CURVE OF A CENTRIFUGAL PUMP P V2 h+ + = Level.of .Mech.Energy ρ f g 2g October 13, 2004 17 Dredge Pumps and Slurry Transport
  • 18. Hman-Q CURVE OF A CENTRIFUGAL PUMP•A rotating impeller of a centrifugal pump addsmechanical energy to the medium flowing througha pump.•As a result of an energy addition a pressuredifferential occurs in the pumped medium betweenthe inlet and the outlet of a pump.•The manometric head, Hman, that is delivered bya pump to the medium, is given as Hman = ( Level.of .Mech.Energy ) p − ( Level.of .Mech.Energy ) s The manometric head, Hman, that is delivered by Pman a pump to the medium, is H man = ρf g October 13, 2004 18 Dredge Pumps and Slurry Transport
  • 19. Hman-Q CURVE OF A CENTRIFUGAL PUMP•A rotating impeller of a centrifugal pump addsmechanical energy to the medium flowing througha pump.•As a result of an energy addition a pressuredifferential occurs in the pumped medium betweenthe inlet and the outlet of a pump.•The manometric pressure, Pman, that isdelivered by a pump to the medium, is given as ρm (Vp2 − Vs2 ) Pman = Pp − Ps + ρm ( hp + hs ) + 2 The manometric head, Hman, that is delivered by Pman a pump to the medium, is H man = ρf g October 13, 2004 19 Dredge Pumps and Slurry Transport
  • 20. Hman-Q CURVE OF A CENTRIFUGAL PUMP Effect of pump speed on Hman-Q & Efficiency-Q (Affinity laws)Effect of solids presence on Hman-Q & Efficiency-Q (Slurry-pumping model) October 13, 2004 20 Dredge Pumps and Slurry Transport
  • 21. Hman-Q PUMP:Affinity Laws (RPM Effect)Pump characteristic curves are:•Hman-Q (Pman-Q),•(Power-Q; pump output power)•η-Q (η is the pump efficiency).The curves hold for a constantpump speed, n [rpm]. October 13, 2004 21 Dredge Pumps and Slurry Transport
  • 22. Hman-Q PUMP:Affinity Laws (RPM Effect)The affinity laws are: Qm,n1 n1 = Qm,n 2 n2 2 H man ,n1  n1  =  H man ,n 2  n2  3 Powern1  n1  =  Powern 2  n2  η f ,n1 =1 η f ,n 2 October 13, 2004 22 Dredge Pumps and Slurry Transport
  • 23. Hman-Q PUMP: Effect of SolidsSolid particles of a pumped slurry diminishthe efficiency of a dredge pump. The ratioof pump efficiencies for mixture and water ηm fc = <1 ηfis also a measure of manometric pressurereduction ρ Pman , m = Pman , f m fc ρfTests of a 0.5-m-impeller pump connected with a 162 kW MAN diesel engine. Speed: 1000 rpm. Pumped material: 0.2 – 0.5 mm sand. October 13, 2004 23 Dredge Pumps and Slurry Transport
  • 24. Hman-Q PUMP: Effect of SolidsThe ratio of pump efficiencies, fc, for sand and gravel slurries fc =1−Cvd ( 0.8 + 0.6log d50 )(Stepanoff, 1965) solids concentration Cvd particle diameter October 13, 2004 24 Dredge Pumps and Slurry Transport
  • 25. H-Q CURVE OF A PIPELINEOctober 13, 2004 25Dredge Pumps and Slurry Transport
  • 26. H-Q PIPELINE: LossesIn a pump-pipeline system the manometric head of apump is required to overcome the total head loss inslurry transported in a pipeline connected to a pump.The total head loss is composed of• the major and minor losses due to flow frictionin a suction pipeline and in a discharge pipeline,• the loss due to the change in elevation of asuction pipeline and of a discharge pipeline,• the losses due to mixture acceleration in apipeline. October 13, 2004 26 Dredge Pumps and Slurry Transport
  • 27. H-Q PIPELINE: Losses1. Major loss(head loss in straight pipeline sections) λ f L Vf2 λ f L Q2 f Hmajor , f = I f L = = D 2g D 2gA2 Hmajor ,m = I m L2. Minor loss 3. Static (geodetic) loss/gain(head loss in fittings) (head loss due to elevation change) V f2 H static, f = ∆h Hmin or , f = ξ 2g ρm H static,m = ∆h 2 V ρm Hmin or ,m = ξ f ρf 2g ρ f October 13, 2004 27 Dredge Pumps and Slurry Transport
  • 28. H-Q CURVES OF A PUMP-PIPELINE SYSTEM October 13, 2004 28 Dredge Pumps and Slurry Transport
  • 29. H-Q SYSTEM: Working PointOctober 13, 2004 29Dredge Pumps and Slurry Transport
  • 30. H-Q SYSTEM: Working RangeOctober 13, 2004 30Dredge Pumps and Slurry Transport
  • 31. Hman-Q SYSTEM: Working RangeChange of Working point:1. the beginning of a cycle: only waterflows through the suction pipe and thedischarge pipe2. the beginning of a soil excavationprocess: the suction pipe is filled withmixture, the discharge pipe is still filledwith water only3. the mixture transportation: both thesuction and the discharge pipes are filledwith mixture4. the end of a cycle: the suction pipe andthe pump are filled with water, thedischarge pipe is filled with mixture. October 13, 2004 Operation at Constant Speed 31 Dredge Pumps and Slurry Transport
  • 32. Hman-Q SYSTEM: Working RangeChange of Working point:1. the beginning of a cycle: only waterflows through the suction pipe and thedischarge pipe2. the beginning of a soil excavationprocess: the suction pipe is filled withmixture, the discharge pipe is still filledwith water only3. the mixture transportation: both thesuction and the discharge pipes are filledwith mixture4. the end of a cycle: the suction pipe andthe pump are filled with water, thedischarge pipe is filled with mixture. October 13, 2004 Operation at Constant Torque 32 Dredge Pumps and Slurry Transport
  • 33. Hman-Q SYSTEM: Working PointChange of Working point:1. R1: the longer pipe: drop in discharge and output power2. R2: the pipe of the original length: maximum output power Effect of Pipe Length3. R3: the shorter pipe: drop in output power, increase in discharge October 13, 2004 33 Dredge Pumps and Slurry Transport
  • 34. Hman-Q SYSTEM: Working PointAdaptation of a dredge pump for a shortened pipeline:The pipeline becomes shorter, the power drops (point A).Remedy: The output power does not drop if a smaller impeller is installed in the dredge pump (point B). Effect of Smaller Impeller October 13, 2004 34 Dredge Pumps and Slurry Transport
  • 35. Hman-Q SYSTEM: Working PointAdaptation of a dredge pump for a shortened pipeline:The pipeline becomes shorter, the power drops (point A).Remedy: The output power does not drop if an impeller with less blades (3 instead of 5) is installed in the dredge pump Effect of Number of Blades (point B). October 13, 2004 35 Dredge Pumps and Slurry Transport