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  1. 1. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522 The Characteristics of a Vertical Submersible Slurry Pump in Transporting Dredged Slurry Prasanta Kumar Sen*, Lal Gopal Das** & Biswajit Halder*** * (PPE, CSIR-Central Mechanical Engineering Research Institute, Durgapur-713209, India) ** (PPE, CSIR-Central Mechanical Engineering Research Institute, Durgapur-713209, India) *** (ME, National Institute of Technology, Durgapur-713209, India)ABSTRACT The performance of vertical centrifugal of the centrifugal slurry pump depends on particleslurry pump is quite different from clear water size, size distribution, shape, solid concentration,pump due to presence of solid particles in water. solid specific gravity, pump speed and certainly onAn approach to derive the performance the pump geometry. The presence of solid particles,behaviour of a vertical centrifugal pump used for specifically coarse particles, in the fluid alwaystransporting dredged slurry based on detail breaks fluid continuum. The bigger the particle sizehydraulic loss analysis has been presented in this worse is the effect. In most of the slurry pumpingpaper. The derived analytical data has been system, particle size distribution is uneven, i.e., it iscompared with experimental results. mixed with fine, medium and coarse particles and itPerformance analysis of a vertical submersible is called heterogeneous slurry.centrifugal slurry pump has been accomplished Previous researchers like Sellgren [1],in two stages. At first, performance Gahlot, et al. [2] and many other eminentcharacteristics of the centrifugal pump with clear researchers developed empirical formulaewater have been investigated considering an in- correlating head reduction ratio (RH) with soliddepth hydraulic loss analysis. Depending on the concentration by weight, solid specific gravity andparticle size distribution, the effect of solid particle size. Performance prediction utilizingparticles on the performance characteristics of empirical correlation carried out by them with thecentrifugal slurry pump has been investigated error band of ±12% to ±20 % for the test slurry.considering volume fraction of particle size. Thehomogenous slurry with fine particles has been Pump head with slurry, H streated as Newtonian fluid with slurry viscosity RH  1  (1)and specific gravity. Additional hydraulic losses Pump head with wate r, H wdue to coarse solid particle have been consideredfor coarse slurry fraction. The performance of The present work has been conducted withthe vertical centrifugal slurry pump has been the objective of detail analysis of several hydraulicpredicted with the accuracies of about 87% and losses occurring in the pump. The fine slurry has90 % for respective solid concentration of 18% been considered as Newtonian fluid. The sameand 10% by volume near the maximum efficiency hydraulic analysis method has been adopted for thepoint. The drooping performance characteristics fine slurry with the slurry viscosity and specificat low flow operation have been found gravity as presented for the centrifugal pumpdeteriorating further with the increase of solid handling clear water. Additional hydraulic headconcentration. losses due to the presence of coarse solid particles have been deducted from the fine Newtonian slurryKeywords – Centrifugal, Diffuser, Impeller, Slurry head by applying the approach as postulated by Roco, et al. [3]. The prediction of the performanceI. INTRODUCTION characteristics of the centrifugal slurry pump has Centrifugal slurry pumps are mostly found been improved by considering the volume fractionin transporting solid grains with carrier fluid through of the solid particles.the pipe lines to the destined point in the processindustries like cement plant, petrochemical plants II. Test Rig & Experimentationand fertilizer plants, etc. Performance characteristics The pilot seabed mining was carried outof any centrifugal pump significantly differ in the from an anchor barge near the Kalvadevi bay ofpresence of solid particles in the fluid from clear Ratnagiri, Maharashtra, India. The seabed miningfluid characteristics. The slurry of uniform particle was carried out by a dredge head with water jets.size is hardly found in industries, rather in most of The dredge head as shown in “Fig. 1” contains athe application particle size varies from few microns water distributor (1) which provides pressurizedto the order of mm. The performance characteristics water to a series of nozzles (2) housed in an agitating 516 | P a g e
  2. 2. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522chamber (3). The pressurized water is suppliedthrough feed line (4) and distributed to the nozzles. Table -1 Water jets from the nozzles cut the seabed Pump Detailsresulting formation of slurry in the dredge head. The Rated Capacity 240 m3/hrsolid concentration in the dredge head is varied by Head 25 mcontrolling the nozzle jet velocity. Capacity Range 75 – 400 m3/hr The test rig of the seabed dredging system Motor Power 35 HPis as shown in “Fig.-2” .The dredge head (1) is Speed 2,900 rpmsuspended from a crane (2) and placed on seabed. No. of stage singleThe horizontal centrifugal pump (3) mounted on theequipment barge (4) sucks sea water through flexible No of vanes in impeller 4hose (5) and discharges high pressure water through Impeller blade inlet angle 18odelivery pipe (6) to the dredge head(1). Impeller blade outlet angle 22.5o The pressurized water released from a set Impeller diameter 198 mmof nozzle cuts seabed resulting formation of solid- No. of vane in diffuser 8water slurry in the agitation chamber of the dredge Water Propertieshead (1).The vertical submersible slurry pump (7) Pumping water Sea watermounted on the dredge head (1) sucks slurry from Temperature 0 – 20 oCthe dredge head and delivers through discharge Specific gravity of clear sea 1.028 – 1.034flexible hose (9) and slurry pipe to the hopper barge water(8). A by pass line (10) with flow control valve (11) Kinematic viscosity (m2/s) 1.83x10-6 to 1.05x10-6regulates the pressurised water supply to the dredge Solid Propertieshead without disturbing the performancecharacteristics of the water supply pump(3). Powerto the equipment is supplied by 320 kVA Diesel Type Seabed sandGenerator Set mounted on the equipment barge. Data Acquisition System for recordingonline data in computer has been installed. Magnetic Specific gravity 2.7 to 3.5flow meter (14), pressure transmitter (15), and Particle size (mm) 0.035 to 0.350ultrasonic solid concentration meter (16) mounted onslurry pipe line. Pressure transmitter (17) &magnetic flow meter (18) are installed on the clearwater pipe line (6). Signal conditioner circuitryconverts signal sensed by the respective transducerin to electrical signal which is transferred to a mastercontroller via RS 485 communication port. Mastercontrollers transmit Data to a personal computer viaRS 232 –C port for on line display and recording inthe hard disk. The investigated pump is single stagecentrifugal impeller and diffuser type casing. Thedetails of the pump and characteristics of sea waterand sea bed sand are listed in Table- 1III. Performance Characteristics with ClearWaterIII.1 Eulers HeadThe energy imparted to the pumping fluid per unitweight of the fluid with infinite number of blades ispopularly known as Euler’s pump head. u 2 c 2 - u 1c 1H th  (2) gConsidering zero inlet pre-rotation of fluid in thedesign. u 2 c 2H th  (3) g 517 | P a g e
  3. 3. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522 Fig 1 Dredge Head Fig 2 Test Rig 518 | P a g e
  4. 4. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522III.2 Slip Table. 2 Hydraulic losses Fluid rotates in the reverse direction of Local Hydraulic Lossesimpeller rotation at the impeller speed after Shock 2entering into the rotating impeller from stationery Losses, w θi h inc  k inc ,condition. Thus, a reverse circulation is set-up in Conrad et 2gblade to blade flow passages. These relative eddies al. [5] kinc = 0.5 to 0.7at the outer edge of the impeller will have (6)circumferential velocity (cөs) in the opposite Mixing hmix 1  1   wake   B   1  1   wake   Losses, Johnston et ci 1 i direction of the outlet whirl velocity (c Ө2) and is 2 known as slip velocity (cөs) al. [6], 2g Mizuki et (7) c al. [7]  i  2 cm 2 1 w2  wake  1  0.45 wm ax Secondary Hydraulic Losses Blade 2 2 u2 Loading hbl  0.05D f (8) Losses, 2g Galvas [8] 0.75H th1 D f  0.3  w1 z  D  D 1  1   2 1  D Fig. 3. Outlet effective velocity triangle with slip u2   2  D2velocity It is depicted in “Fig. 3”. It has beenstudied by many researchers that Weisner’s[4] slip u 2 c 2model gives realistic slip factor and same has been H th1  2 u2considered for the present work. Friction c  f  1  s Skin 1 2 L u2 Friction, hf  wm  (10) Musgrave 2 dh sin  2 (4) f 1 [9] 1 w d  z 0 .7  2 log 10  m hm    0.8 u c - c  (5)    H th  2  2 s Clearance Flow g Clearance q  zsLu cl cl losses, (1 Augier PclIII.3 Hydraulic losses in the impeller u cl  0.816 1) The fluid while passing through the [10] impeller or diffuser flow passages encounters Qr2 c 2  r1c1 several hydraulic losses which reduces the effective Pcl head developed by the pump. Roco et al [6] zrbclassified the hydraulic losses as local hydraulic r  r  r 1 2 b b1  b2 losses, secondary hydraulic losses and frictional 2 2losses. The optimum hydraulic loss model has beenconsidered in the present study which is shown inTable-2. IV. Property of Homogeneous Solid Liquid Mixture:III.4 Diffuser Losses It has been experimented that particles of Hydraulic losses in the diffuser are size below 70 µm remains suspendedcalculated in the similar manner as impeller but a homogenously in water. Viscosity of such finestationary frame of reference is considered. solid liquid homogeneous mixture has been calculated using Thoma’s [11] correlation and mixture specific gravity as listed below. 519 | P a g e
  5. 5. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522 2   v* 1m  w 1  2.5Cv  10.5Cv 2 2 (12) Frsl  ad p ( s  1)  s l 2 100 cm  (13) Where, a  2 , C w (100  Cw ) r2  s w c v*   b V. Effects Of Solids on Pump Performance 5.98  5.75 log10  2  The centrifugal pump behaves in a quite  2kimp   different manner in presence of solid particles in 0.5the pumping fluid. Solid particles can slip from the acarrier fluid, i.e., the particles move at a slower or a W (a, C v )  Wo   (1  C v ) E gfaster velocity than the carrier fluid or it can move  with same velocity as carrier fluid depending on The value of E is taken from E vs. Particlethe particle size, particle specific gravity and solid Reynolds Numbers curve as given by Gandhi, et al.concentration. [12] Roco, et al. [6] considered the additionalhead losses due to presence of solid particles in the H  f  1100Cw(s  1) gd p Wo (17) H  slfluid. They classified the hydraulic losses in threeclasses, viz., local losses, secondary losses and f f c2 cfrictional losses. The additional hydraulic lossesdue to the presence of solid particles have been VI. Experimental Uncertainty.estimated by correlation with three non- Table. 2 Uncertainty of the instrumentdimensional numbers namely, particle Reynolds Instruments Make % ofnumber, Froude number and pump specific speed. ErrorIt has been observed that the solid particle sizes Magnetic Flow Manas 0.75%below 70 µm remain homogenously suspended in Meter Microsystems Pvtthe fluid and such particles are treated as fine Ltd, Indiaparticles. Homogenous slurry of fine particles in Pressure WIKA 0.50%which particles are evenly distributed behaves like Transmitter Instruments Indiaa clear continuum liquid and it can well be treated Pvt. Ltdas Newtonian fluid with its specific gravity and Ultrasonic Solid Rhosonics 0.10%viscosity. Coarse particles (70 to 350 µm) are Concentration Analytical BV,unevenly distributed in the fine homogeneous meter Netherlandslurry. The analysis has been done consideringcoarse particle mean size, d50 = 250 µm and that ofthe fine particles are of 50 µm. The hydraulic VII Results and Discussion The performance test of a verticallosses have been estimated considering two volume submersible slurry pump has been accomplishedfraction of particles as described above. In brief,hydraulic losses occurred in the pump flow passage with 18 % and 10 % solid concentration by volumeare caused by fine homogenous slurry fraction and and same has been done analytically. It has beenthe additional losses by the coarse slurry fraction. observed that analytical performance curveHydraulic losses (HL) for centrifugal slurry pump matches very closely to experimental curve at the best efficiency point (bep) ( 254 m3/ hr.) with theare analysed as below. accuracy of about 87% and 90% for solid concentration by volume (C v) of 18% and 10% HL total   HL f   HLsl (14) respectively. The present experimentation has beenH  Re sl conducted from minimum to maximum flow rate  297C v ( s  1) sf sl with clear water as well as with slurry by opening H sf f Ns (15) the discharge valve gradually. It has been observed that the predicted and the experimentalH loc sl 10.8Cv  s  1 performance curve intersect at some flow rate  (16) H loc  f Frsl towards the left of the best efficiency point and these curves closely match in the region from bep w(a, cv )d p to intersection point. As the pump flow reducesRe sl  from bep operating conditions or in other words the  flow velocity reduces, hydraulic head losses as well as the additional head losses due to solid particles 520 | P a g e
  6. 6. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522decreases although the pump fluid flow remains inthe turbulent region (Re ~ 6 x 105 ) with leastfriction factor. So, in the region from bep tointersection point, predicted performance curvesclosely match with the experimental curves. It isindicated in Fig.2 and Fig.3. It is also found thatfrom intersection point to the end of the curve,head of the predicted performance curve is higherthan the experimental curve for slurry application.The predicted heads are 24% and 15% higher thanthe experimental heads at the flow rate of 300 m3/hr. for Cv of 18% and 10% respectively. Theexcessive additional head losses due to thepresence of coarse solid particles at high flow Fig. 3. Performance Curve (18% solid Conc.)region may cause this deviation, which could notbe captured accurately in the presented analytical I: Experimented with clear watertechnique. A drooping (stall) performance II: Predicted with clear watercharacteristics in both the experimental and the III: Predicted with seabed sand slurrypredicted performance curves have also been (Conc. 10% by volume)observed at an operating point in the reduced flow IV :Tested with seabed sand slurryregion. It happens due to steep divergence in blade (Conc. 10% by volume)to blade flow passages. Fluid moves against thepositive pressure gradient which thickens theboundary layer and finally it separates from theimpeller wall surfaces. Eddy formation takes placein the separated region which causes hugehydraulic losses and it is further deteriorated due topresence of solid particles. The pump again tries todevelop higher head to match with the dischargepressure which further increases hydraulic losses.As a result, the head developed by the pump againfalls and the pump operation at this flow rate isunstable. These unsteady flow fluctuationpropagates throughout the impeller and diffuserflow passages and the pump experiences stall. Fig. 4. Performance Curve (10% solid Conc.)Pump performance at this low flow region is also .found to deteriorate further with the increase of VIII. Conclusionsolid concentration, i.e., it is more prominent when Analysis of performance characteristics ofthe pump handles slurry of solid concentration by centrifugal slurry pumps considering the volumevolume 18% than that of 10%. The dotted lines in fractions of solid particle depending on particle sizeFig. 2 and Fig. 3 show the expected performance and particle distribution gives improved resultscurves at reduced flow rate while the experimental than considering a mean particle size. Thecurves deviate from it. presented method gives reasonably accurate results around the best efficiency point. However, further research, in-depth study and experimentation isI: Experimented with clear water really needed for performance analysis ofII: Predicted with clear water centrifugal slurry pump when it handles highlyIII: Predicted with seabed sand slurry coarse slurry with varied particle size. (Conc. 18% by volume) AcknowledgementIV :Tested with seabed sand slurry The work has been conduced in network (Conc. 18% by volume) project of Capacity Building of Coastal Placer Mining led by Council of Scientific & Industrial Research, New Delhi, India. Authors are duly acknowledged to the Director, CSIR–Central Mechanical Engineering Research Institute, Durgapur, India for his kind support and permitting to publish this paper. 521 | P a g e
  7. 7. Prasanta Kumar Sen, Lal Gopal Das, Biswajit Halder / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.516-522Nomenclature [3] M.C. Roco, M. Marsh, G.R. Addie, anda characteristics local acceleration (m/s2) Maffett, , Dredge pump performance J.R.bep best efficiency point prediction, J. Pipelines 5(1985) 171-190b impeller width (m) [4] F.J. Wiesner, A review of slip factors forCv concentration of solids in the slurry by volume incentrifugal impellers, ASME J. Eng. for decimal fractionCw concentration of solids in the slurry by weight(%) (1967) 558—576 Power, 89c velocity of flow (m/s)[5] O. Conrad, K. Raif and M.Wessels, Thedp solid particle size (m) calculation of performance maps ford50 particle size, 50% by weight passing through centrifugal compressors with vane-island the sieve diffusers. In Proceedings of the 25thdhm hydraulic mean diameter (m) ASME Annual International Gas TurbineD impeller diameter (m) Conference and the 22nd ASME AnnualDf diffusion factor Fluids Engineering Conference onFr Froude number Performance Prediction of Centrifugals clearance gap width (m) Pumps and Compressors, New Orleans,ρ specific gravity Louisiana (1980) 135–147.v* friction velocity (m/s) [6] J. P. Johnston and Jr, R. C.Dean, Losses inc’θ corrected whirl velocity (m/s) vaneless diffusers of centrifugalw relative velocity (m/s) compressors and pumps.Wo unhindered particle settling velocity (m/s) Analysis,experiment, and design, Trans.W(a,Cv) modified particle settling velocity(m/s) at ASME, J. Engg Power 88(1966) 49–62local acceleration (a) and solid concentration(Cv) [7] S. Mizuki, I. Ariga and I. Watanabe,z no of vanes Prediction of jet and wake flow withing gravitational acceleration(m/s2) centrifugal impeller channel, Inu impeller peripheral speed (m/s) Proceedings of the 25th ASME Annualhinc incidence head losses (m) International Gas Turbine Conferencehmix mixing head losses (m) and the 22nd ASME Annual Fluidshbl blade loading losses (m) Engineering Conference on Performancehf frictional head loss (m) Prediction of Centrifugal Pumps andL blade mean streamline meridional length (m) Compressors, New Orleans,kinc incidence loss coefficient Louisiana(1980) 105–116.kimp impeller flow coefficient [8] M. R. Galvas, Analytical correlation ofNs pump specific speed (SI) centrifugal compressor design geometry∆pcl clearance pressure loss (N/m2) for maximum efficiency with specificQ pump flow rate (m3/s) speed, NASA Technical Note T.N.-Q flow rate (m3/s) D6729(1972)r impeller radius (m) [9] D.S. Musgrave., The prediction ofRe Reynolds number design and off design efficiency forβ blade angle centrifugal compressor impellers, Inλ friction coefficient Proceedings of the 25th ASME Annualεwake width of wake (dimension less) International Gas Turbine Conferenceν kinematic viscosity (m2/s) and the 22nd ASME Annual FluidsSubscripts Engineering Conference on Performance1 impeller inlet f fluid, fine slurry Prediction of Centrifugal Pumps and2 impeller outlet s slip, solid Compressors, New Orleans, LouisianaӨ sl slurry tangential (1980) 185–189.cl sf secondary flowclearance [10] R. H. Augier, Mean Streamline aerodynamic performance analysis ofReferences centrifugal compressors, Trans ASME,88 [1] A., Sellgren, Performance of Centrifugal (1966) 49 – 62. Pumps When Pumping Ores and Industrial [11] D.G. Thomas, Transport properties of Minerals, Proc. Hydro transports-6, suspensions: VIII. A note on the viscosity Paper G1, BHRA Fluid Engineering of Newtonian suspensions of uniform (1979) 291-304. spherical particles. J. Colloid Science, 20, [2] V. K. Gahlot, V. Seshadri, and R.C. 267-277 (1965). Malhotra, Effect of Density, Size, [12] B. K Gandhi, S.N Singh, and V. Seshadri, Distribution and Concentration of Solid on Improvement in the prediction of the Characteristics of Centrifugal Pumps, performance of centrifugal slurry pumps Trans. ASME, J. of Fluid Engg., Vol 114 handling slurries, Proc. Instn. Mech. (1992) 386-389. Engrs Vol 214, part-A (2000) 473 -486 522 | P a g e