MEASUREMENT & MONITORING
PUMP LIFE EXPECTANCY
SULZER
ENSURING FEEDWATER PUMP RELIABILITY
THROUGH PROACTIVE SITE PERFORMANCE TESTING
Chris Muscavage, Field Technical Service
Engineer, at Sulzer, looks at the importance
of pump performance testing and how it can
improve plant reliability.
Fossil fuels continue to be the primary
source fuel for power generation which,
according to the U.S. Energy Information
Administration in 2017, accounted for 62.7%
of capacity with nuclear capacity accounting
for an additional 20%. This equates to nearly
83% of U.S. power being wholly or partially
reliant upon steam generation utilizing
feedwater pumps.
Deregulation has given rise to an open
market where pump “design point” and
actual “operating point” may no longer be
equivalent and may vary significantly. Such
market-driven conditions primarily affect
combined-cycle, coal, and biomass-fueled
generators during Independent System
Operator (ISO) dispatch control. Where is
my pump operating? Which pump should
take overhaul priority? These are certainly
valid questions regarding asset availability,
reliability and the associated financial
consequences of “abnormal operation”.
Where is my pump operating?
In the following example, one boiler
feedwater pump (BFP) was selected from
a group of eight where proactive field
performance testing was accomplished.
Performance testing was employed
to provide the owner/operator with
quantifiable pump condition data to aid in
prioritizing unit overhaul schedules. This
particular generation facility is configured
with six separate combined-cycle units
employing 12 feed water pumps. The
example pump is one of eight axial-split,
multi-stage, ring-section pumps. At the time
of field performance testing, gross facility
generation was limited by ISO dispatch to
60 percent of full generator / heat recovery
steam generator (HRSG) load.
indicating satisfactory performance, subject
pump hydraulic results show operation at
58% of BEP. This is a surprisingly common
situation in the current generation market.
In addition, in cases where the pump’s NPSHr
curve rises with a reduction in capacity, the
NPSHa may be insufficient to overcome the
on-set of cavitation. Operation at lower than
recommended BEP flows can result in pump
inlet flow recirculation leading to increased
vibration, wear and reduction in mean-time-
between-repairs (MTBR).
[FIGURE 3]
Pump mechanical integrity is also evaluated
in addition to hydraulic testing with real-
time vibration data being captured and
analyzed. BFP C1 vibration response showed
clear indication recirculation at the suction
side and BFP C2 exhibited similar response
to a lesser degree. Vibration data were
consistent with pump hydraulic results and
leak-off rates. The facility prioritized overhaul
scheduling accordingly.
Which pump should take overhaul priority?
Example 2 considers the same group of eight
pumps as considered in example one. By
prioritizing time-based overhaul scheduling
founded on actual unit performance, the
owner/operator can maximize unit reliability
and availability.
Further mechanical evaluation is
accomplished using infrared thermal imaging,
visual inspection of pump, seals, lube oil
system, coolers, baseplate, foundation, and
grouting.
[FIGURE 2]
Figure 2 shows boiler feedwater pump (BFP)
C1 hydraulic performance results which
are indicative of degraded or less than
optimal internal clearances. Note that results
fall below the OEM test curve indicating
unsatisfactory performance and that flow
capacity is limited to 51% of BEP.
Balance line leak-off rate is an excellent and
well-documented indicator of internal wear.
Figure 3 graphically tabulates leak-off rates of
the eight subject pumps and, as expected, the
largest flow rate recorded was at BFP C1.
In taking this comprehensive approach to
pump performance testing from both the
hydraulic and mechanical perspectives, an
experienced field engineer is able to then
provide the end user with detailed analyses
and recommendations relative to in-service
pump performance.
Field performance testing of critical feedwater
pumps provides the owner/operator with
quantifiable results and recommendations for
their pump(s) in service at plant generation
conditions. Proactive periodic testing
raises the reliability bar another notch by
establishing a benchmark for comparison
which removes any question of pump
condition. Annual or bi-annual performance
testing of a facility’s heart is highly
recommended.
[FIGURE 1]
Figure 1 shows pump hydraulic performance
“as found”. Note how far to the left of best
efficiency point (BEP), shown in blue, test
results, shown in red, fall on the original
equipment manufacturer (OEM) test curve.
Critical pump operation is expected to fall
within 70-120% of BEP. In this case, although
test results fall directly on the test curve
116
PECM Issue 39
Sulzer Turbo Services Houston Inc.
: Jennifer Cardillo, Marketing and
Communications Manager, Americas
Rotating Equipment Services
Tel: +1 713 567 2706
Web: www.sulzer.com
Email: [email protected]