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Optimum overhaul of pumps 2014


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Pumps are used in virtually all industries and are big uses of energy. This presentation shows methods of condition monitoring and how to optimise time to overhaul.

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Optimum overhaul of pumps 2014

  1. 1. How to reduce the energy used by your pumps Ray Beebe Speaker, trainer, author, including: Predicting maintenance of pump using condition monitoring (Elsevier, 2004)
  2. 2. Pumps World’s most common machine (after motors) Use 25% of world’s total motor-driven electricity, ….or about 6.5% of global electricity production!!
  3. 3. C o n d itio n m o n ito rin g te ch n iq u e s V ib ra tio n a n a lysis (ro ta tin g m a ch in e s) P e rfo rm a n ce a n a lysis A n a lysis o f we a r p a rticle s a n d co n ta m in a n ts V isu a l in sp e ctio n /N D T E le ctrica l p la n t te sts ….for pumps: Bearing degradation - Oil sampling & analysis, vibration analysis Casing wear? - NDT Misalignment? - Vibration Internal wear, impeller and seals? - Performance analysis
  4. 4. Optimise energy usage – good for business AND greenhouse effect. Choose the best mix of techniques to detect and monitor the modes of degradation you expect.
  5. 5. Pump internal wear •Erosion of impeller Increased clearance allows recirculation •Erosion at sealing/ wearing rings
  6. 6. Pump internal wear Ring section diffuser pump Sealing rings Internal leakage
  7. 7. Pump internal wear Internal leakage recirculation Head H H-Q with wear Flow Q
  8. 8. Pump internal wear Increasing internal leakage reduces Head at chosen datum flow % Reduction in head Head reduction @ datum flow shows cooling water pump degradation (230kW) 20 15 10 5 0 0 500 1000 Days in service 1500
  9. 9. Close to linear for 4500kW pump, too Boiler Feed Pump wear trend % reduction in Head @ datum flow 2 0 -2 0 1 2 3 4 5 6 7 8 9 -4 -6 -8 -10 y = -0.155x2 + 0.4907x - 0.1388 -12 Time: years since overhaul 10
  10. 10. § Effect of increased internal wear in centrifugal pumps relates to Specific Speed: § Using data at Best Efficiency Point: N = Rotation speed, r/min Q = flow per impeller eye, m³/h H = head per stage, m (Number resulting is close to that you get if US units are used) Ns N H Q 0 . 75
  11. 11. 20 Clearances worn to 2X design 18 16 14 12 % Increase in 10 power 8 Clearances worn to 1.5X design 6 4 2 0 0 1000 2000 3000 Specific Speed (US units) 4000 5000
  12. 12. 1 Head-Flow method for CM § At around normal duty point is enough. § Checks condition of pump AND its system. § Repeatable pressure and flow measurement needed, and speed for variable speed pumps.
  13. 13. •Plant DCS etc may work for monitoring: e.g. boiler feed pump operating H-Q point
  14. 14. DCS use off-line: historian § Boiler Feed Pump
  15. 15. Pressure measurement
  16. 16. Pressure measurement: quick connect couplings for non-hazardous liquids
  17. 17. Flow measurement: orifice plate Repeatability can be OK even if very short straight upstream pipe length!
  18. 18. Annubar™ and similar
  19. 19. Expedient flow measurement: ultrasonic flowmeter (Several types) [Note: pipe bore diameter must be known. If test flow seems unusual, check pipe wall thickness for presence of buildup in bore]
  20. 20. Flow measurement: tank in system: measure level change with time.
  21. 21. 2 Shut-off Head § Simple test § Not always allowable: high energy pumps can explode if dead-headed too long § Note that pumps with a rising head-flow curve shape can give a greater shutoff head when worn!
  22. 22. Waste water pump, 19kW, Specific Speed 930
  23. 23. 3 Measurement of thrust Annular clearance balance leakoff flow wears: thrust balance flow increases, ……therefore likely that clearances up at the impellers, too.
  24. 24. •Thrust balance flow line is small diameter; low cost permanent flow monitor possible. •High temp ultrasonic flow sensors available
  25. 25. Boiler feed pump, variable speed (flow is proportional to speed, therefore was corrected to datum speed). This corresponds to 250kW wasted ! PLUS any impeller sealing leakage!
  26. 26. 4 Thermometric method § Assumes inefficiency shows as increase in liquid temperature through pump § Well established in UK etc. water industry l Special tapping points, 2D from suction, discharge flanges (temp, pressure) l Power measured: motor efficiency found l Flow can be calculated l Proprietary systems available
  27. 27. Thermodynamic process: use liquid properties (water/steam: 3 2: P2 T2 Enthalpy 1: P1 T1 Entropy
  28. 28. § or use Whillier equation: for water up to 54 degC (Units: degC, kPa, K) 100 [1 0 . 003 ( Inlet temp 2) 4160 Temp rise Total Head ]
  29. 29. Yatesmeter, also Robertson’s kit…
  30. 30. Pressure, temperature transducers at suction and discharge, away from pump flanges Precision power meter Notebook takes data, calculates flow, efficiency
  31. 31. Thermometric tests on boiler feed pump with pipe surface temperature •Usable results, BUT must allow time for outlet metal temp to stabilise.
  32. 32. Optimum time for overhaul - on energy saving basis (1) § 1 Pump wear causes drop in plant production • Overhaul readily justified § 2 Pump duty is intermittent to meet demand • Wear means extra service time and extra energy
  33. 33. Optimum time for overhaul - on energy saving basis (2) § 3 Pump wear does not affect plant production, at least initially. Constant speed, output controlled by throttling – monitor control valve position § 4 Pump wear does not affect plant production, at least initially. Output controlled by varying speed – monitor pump speed •Same basic method applies...
  34. 34. An example: § Overhaul would cost $50 000. § Cost of power 10c/kWh. § Pump runs for 27% of time on average § Test at 24 months since last overhaul
  35. 35. § Motor efficiency is 90%, so the extra power consumed by motor/pump combined (WORN) is: 2300 – 2150 = 150kW ÷ motor efficiency = 167kW
  36. 36. § Calculate the current extra cost of electricity: (720h is average month): 167 × 0.10 × 0.27 × 720 kW $ = $3240/month % h
  37. 37. § Calculate the average cost rate of deterioration: $ 3240 ÷ 24 = $ 135 /month/month. Can now find the optimum time for overhaul: T 2O C = 27.2 months
  38. 38. Total cost curve often fairly flat around the optimum
  39. 39. Variable speed pump (1)
  40. 40. Variable speed pump (2) • Same method as before used, but with speed change. Here, 31% increase in power to maintain constant system flow, as speed increases from 1490 to 1660 r/min
  41. 41. The method does not apply to all pumps….. §Small pumps may cost more to test than overhaul, and energy costs may be just too small to justify work §Pumps of Specific Speed above about 2000 (r/min, m3/h, m or US units) have a flat or declining Power-Flow curve, and increased leakage does not use more power
  42. 42. Is the pump always at fault?
  43. 43. Maybe the system has changed?
  44. 44. Note that a lower system resistance is also possible
  45. 45. Is the rotation correct? (DC motor drive)
  46. 46. Conclusion § Condition monitoring is much more than vibration analysis § Performance analysis adds the energysaving dimension - USE IT !
  47. 47. Happy Monitoring ! [Co-ordinator for 16 years of Monash University’s postgrad programs in maintenance and reliability engineering: off campus learning (open to all: conditions apply). From Jan 2014, programs owned and run by Federation University Australia]