Overhaul Instructions CP-4 Centrifugal Fire Pumps Form No ...
Optimum overhaul of pumps 2014
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Transcript of Optimum overhaul of pumps 2014
How to reduce the energy used by your pumps
Ray Beebe Speaker, trainer, author, including:
Predicting maintenance of pump using condition
monitoring(Elsevier, 2004)
World’s most common machine (after motors)
Use 25% of world’s total motor-driven electricity,
….or about 6.5% of global electricity production!!
Pumps
….for pumps:Bearing degradation - Oil sampling & analysis, vibration analysisCasing wear? - NDTMisalignment? - VibrationInternal wear, impeller and seals? - Performance analysis
Vibra tion ana lysis (ro ta ting m ach ines)
Perform ance ana lysis
Ana lysis o f wear partic les and contam inants
V isua l inspection /N D T
E lectrica l p lan t tests
C ondition m onito ring techn iques
Optimise energy usage – good for business AND greenhouse effect.
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.
Choose the best mix of techniques to detect and monitor the modes of degradation you expect.
Pump internal wear
• Erosion of
impeller
• Erosion at sealing/ wearing rings
Increased clearance allows recirculation
Pump internal wear
Sealing rings
Ring section diffuser pump
Internal leakage
Pump internal wear
Head
H
Flow Q
Internal leakagerecirculation
H-Q with wear
Pump internal wear
0
5
10
15
20
0 500 1000 1500
Days in service
% R
ed
uct
ion
in h
ead
Head reduction @ datum flow shows cooling water pump degradation (230kW)
Increasing internal leakage reduces Head at chosen
datum flow
Close to linear for 4500kW pump, too
y = -0.155x2 + 0.4907x - 0.1388
-12
-10
-8
-6
-4
-2
0
2
0 1 2 3 4 5 6 7 8 9 10
% r
ed
uc
tio
n in
He
ad
@ d
atu
m
flo
w
Time: years since overhaul
Boiler Feed Pump wear trend
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) 75.0H
QNN s
0
2
4
6
8
10
12
14
16
18
20
0 1000 2000 3000 4000 5000
Specific Speed (US units)
% Increase in power
Clearances worn to 2X design
Clearances worn to 1.5X design
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.
• Plant DCS etc may work for monitoring: e.g. boiler feed pump
operating H-Q point
DCS use off-line: historian
Boiler Feed Pump
Pressure measurement
Pressure measurement: quick connect couplings for non-hazardous liquids
Flow measurement:
orifice plate
Repeatability can be OK even if very short straight upstream pipe length!
Annubar™ and similar
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]
Flow measurement: tank in system: measure level change with time.
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!
Waste water pump, 19kW, Specific Speed 930
3 Measurement of thrust balance leakoff flow Annular clearance
wears: thrust balance flow increases,
……therefore likely that clearances up at the impellers, too.
• Thrust balance flow line is small diameter; low cost permanent flow monitor possible.
• High temp ultrasonic flow sensors available
This corresponds to 250kW wasted !
PLUS any impeller sealing leakage!
Boiler feed pump, variable speed (flow is proportional to speed, therefore was corrected to datum speed).
4 Thermometric method
Assumes inefficiency shows as increase in liquid temperature through pump
Well established in UK etc. water industry Special tapping points, 2D from suction,
discharge flanges (temp, pressure) Power measured: motor efficiency found Flow can be calculated Proprietary systems available
Thermodynamic process: use liquid properties (water/steam: www.pepse.com)
Entropy
Enthalpy
3 2: P2 T2
1: P1 T1
or use Whillier equation: for water up to 54 degC
(Units: degC, kPa, K)
]4160)2(003.01[
100
HeadTotal
riseTemptempInlet
Yatesmeter, also Robertson’s kit…
Precision power meter
Notebook takes data, calculates flow, efficiency
Pressure, temperature transducers at suction and discharge, away from pump flanges
Thermometric tests on boiler feed pump with pipe surface temperature
• Usable results, BUTmust allow time for outlet
metal temp to stabilise.
Optimum time for overhaul - on energy saving basis (1)
1 Pump wear causes drop in plant production
2 Pump duty is intermittent to meet demand
• Overhaul readily justified
• Wear means extra service time and extra energy
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...
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
Motor efficiency is 90%, so the extra power consumed by motor/pump combined (WORN) is:
2300 – 2150 = 150kW ÷ motor efficiency
= 167kW
Calculate the current extra cost of electricity: (720h is average month):
167 × 0.10 × 0.27 × 720
kW $ % h
= $3240/month
Calculate the average cost rate of deterioration:
$ 3240 ÷ 24 = $ 135 /month/month.
Can now find the optimum time for overhaul:
= 27.2 months
C
OT
2
Total cost curve often fairly flat
around the optimum
Variable speed pump (1)
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
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
Is the pump always at fault?
Maybe the system has changed?
Note that a lower system resistance is also possible
Is the rotation correct?
(DC motor drive)
Condition monitoring is much more than vibration analysis
Performance analysis adds the energy-saving dimension - USE IT !
Conclusion
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]