Feedwater System Reliability
Users Group – 2012 Meeting
Feedwater Heater Level
Optimization
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Introduction:
 True
North Consulting, LLC
◦ Phone (970) 252-1489

Frank Todd – Mgr. Thermal Perf. Group
 Phone (856) 391-3347
 fdt@tnorthconsulting.com

Iver Jacobson—Sr. Consulting Engineer
◦ Phone (479) 967-5077 or (479) 280-9072 (cell)
◦ ijj@tnorthconsulting.com
Heat Exchanger Training
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Terminal Objective
Familiarize the attendee with the
importance of feedwater heater level
optimization and the associated issues
with establishing the best operating level.
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Enabling Objectives
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Understand physical impact of variations in FWH
operating level.
Understand the knee curve for DCA.
Review reasons for changing operating level.
Review causes for incorrect level indication.
Understand basic FWH level test process.
Review precautions for an event-free test.
Understand impact of degraded FWH internals on test
results.
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Feedwater Heater Level
Feedwater Heater Optimum Level:
1. Below active tubes (thermal efficiency)
2. Flooded enough to prevent drain cooler
entrance steam in-leakage or flashing.
(reliability)
Achieve maximum reliability as main target and
optimum DCA & TTD as secondary.
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Feedwater Heater Level
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Feedwater Heater Level
Knee response of DCA to FWH level.
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Feedwater Heater Level
In conjuction with the degrading DCA, flow
velocity in the DC increases due to the twophase flow, causing vibration damage.
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Feedwater Heater Level
Two-phase flow and high tube vibration can cause
loss of baffle plates and tube failure.
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Feedwater Heater Level
Why isn’t original FWH level still ok?
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Error / mistake in establishing
Tube plugging (lower rows) – increases dp
before drains are sub-cooled (flashing)
Flow increase – uprate, turbine changes, lower
FW inlet temperature
Higher DC inlet dp – debris in bottom of shell
at DC entrance.
Unstable LCV (cycling) causes level swing
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Feedwater Heater Level
Is my indicated FWH level correct?
The originally specified level may be suitable for operation,
but the indicated level may not accurately reflect actual
level at the drain cooler entrance.
Best Fix – Level Test
A level test can establish an appropriate operating level “as
indicated” (don’t need absolute value).
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Feedwater Heater Level
Why is indicated FWH level wrong?
(Reference HEI – Closed Feedwater Heaters, App. A.2.4; $450)
 Excess steam condensing in level gauge pipe (i.e. uninsulated pipe
run, or excessive length)
 High velocity past top pipe connection (see pic.)
 Sediment/blockage in bottom level leg.
 Loop seal trapping condensate in top leg (rare)
 Improperly installed, closed, or stem-disc separation in level
instrument piping valves
 Level tap connection location away from DC entrance.
 “Heater level should always be established by a test.”
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Feedwater Heater Level
Vendor Generic FWH Example Diagram:
Notice large spacing between steam nozzle and liquid level
connection.
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Feedwater Heater Level
FWH Shell Diagram (actual)
Notice proximity of level connection taps and steam
nozzle (i.e. high velocity past level tap)
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Feedwater Heater Level
Potential indicators level is not optimum?
1.
2.
3.
4.
5.
DCA – elevated compared to design, opposite train,
or historical values, or unstable value.
TTD – higher than design and DCA is either normal
or lower than design. (high level)
Tube degradation / failure in drain cooler.
Noise (popping, banging, thumping) in shell.
Cycling or difficult to tune/damp LCV
FWH level is only one of many possible causes.
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Feedwater Heater Level
I have “symptoms” of needing a level test.
What are my options?
Raise operating level w/o test.
2. Perform FWH level test(s).
1.
A. In-house or with fleet and peer support
B. External contracted support.
3.
Improve conditions (i.e. insulate pipe, tune
controllers to address level oscillation)
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Feedwater Heater Level
Raise FWH Operating Level
+ Simpler than a test, reduces risk.
+ Improvement often seen w/ +1”to +3”
+ Minor engineering eval. (typically)
Consider margins to alarm & dump valve
 Consider stability of controller
 Consider physical range of displacer tube.

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Feedwater Heater Level
FWH level controller devices
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Feedwater Heater Level Test
Level Test - Simplified Summary
Step 1: Raise level to high level constraint.
Step 2: Record data after stabilized.
Step 3: Lower level in steps to low constraint.
Step 4: Record stabilized data at each step.
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Feedwater Heater Level Test
High level constraint:
Typically high-level alarm
 May be upper adjustable range of normal controller
Low level constraint (first reached):
 Low level alarm
 Sharp increase in DCA or noise in shell
 Lower adjustable range of normal level controller
 Bottom of level indicator/sight glass
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Feedwater Heater Level Test
Simple Concept – but Beware!
FWH level tests must be:
- Well planned. (be thorough)
- Well communicated. (be engaged)
- Well executed. (be deliberate)
FWH level tests have been performed at
hundreds of sites on thousands of heaters for
more decades than you have lived.
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FWH Test Considerations
Always Remember Murphy’s Law!
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Whatever can go wrong, will go wrong!
It will go wrong at the worst possible time!
It will go wrong on the worst component!
It will all be remembered as your fault!
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FWH Test Considerations
Not a fun day at the office:
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FWH Test Considerations
Much faster turbine disassembly with
improved lighting and ventilation.
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FWH Test Considerations
1. Learn from others mistakes/misfortunes. Study
and use related OE.
2. Establish team – System Engineer, Operator and
I&C tech. Engage/involve team in all phases.
3. Know level instrument setpoints and actions
(alarms, dump valve open, bleeder trip release,
heater bypass/isolation)
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FWH Test Considerations
4. Develop contingency plans and exit strategies
for off-normal conditions or responses.
5. Ensure affected level equipment is available and
functioning properly before the test. (including
downstream heaters or drain tanks)
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FWH Test Considerations (contd.)
6. Consider supplemental instruments (e.g.
acoustic monitoring to detect shell noise)
7. Level controller response may be poor near
extremes of adjustable range.
8. Steam flow into drain cooler at knee may cause
control oscillations.
9. Consider affects on other components (other
FWHs, drain tanks, MSR, etc.)
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Feedwater Heater Level
Example of FWH Level Values:
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Feedwater Heater Level
EPRI TR-1003472: Level Control Guide
Good resource. Be familiar, but be careful (not perfect).
 “Do not rely on the manufacturer’s markings.”
 Perform level tests on all heaters (justification?)
 Re-perform level test after tube plugging (if extensive)
 Level testing (Sec. 7.3) – discusses option of raising level by
manually closing LCV (not recommended)
 Knee indications list: rapid change in DCA (maybe), and
drain outlet pressure (unlikely), and increase in flow noise
(may not be detected)
 Good OE summaries/examples in App. E.
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Feedwater Heater Level
Level Tests – “Different Results”
The knee may be less obvious, or if found, DCA may
remain elevated at levels well above it:
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Drain cooler breach may exist above the range of the level
test.
Control room level indication errors and/or Ops procedure
limits may not allow knee to be reached.
Tests at higher levels are possible, but require greater
precautions.
Request shell-side inspections if high DCA remains above
knee (particularly if tube damage exists).
New optimum level may require setpoint and/or physically
raising level instruments.
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Feedwater Heater Level
If a breach in the drain cooler shroud exists, its size and
location will affect level test results.
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Feedwater Heater Level
Drain cooler shroud degradation example.
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Feedwater Heater Level
Loose material in the shell is a “wild card”.
Failed shell liners, plates, tubes, tools, etc. may
relocate during flow transients.
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Feedwater Heater Level
Sustained operation with tube leaks is a common
cause of sheared tube fragments in the shell.
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Feedwater Heater Level
Level Test Potential Benefits:
 Improved Reliability – arrest or slow degradation
 Reduced O&M Cost – longer PM intervals for ECT.
 Reduced Capital Cost – longer service life
 Efficiency Gain – more MW
 Improved level control stability
 Reduced wear/tear on control valves
 Improved overall system stability
 Knowledge – improved basis/justification for more intensive
inspections or repairs to address condition.
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Feedwater Heater Level
Potential Actions/Changes from Level Test:
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Operating Level (normal, high level dump)
Setpoint Changes (alarms, interlocks)
PM Intervals (ECT extended per reduced damage rate)
Shell-side Internals Inspection
FWH Condition Assessment Evaluation
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Feedwater Heater Level
Portable ultrasonic instruments, such as UE
Systems Ultraprobe, can be useful during
walkdowns, monitoring, or level tests.
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Feedwater Heater Level
Summary of FWH Level Optimization:
1.
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4.
5.
Optimum level maximizes reliability and to the extent
possible efficiency.
Previous operating levels may be unsuitable due to
changed conditions in system or FWH.
Indicated level may not be accurate.
Level tests are used to determine best level.
Level tests require careful planning/execution.
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Feedwater Heater Level
Questions / Comments?
Contacts:
Frank Todd
Iver Jacobson
Manager Thermal Performance
Sr. Consulting Engineer
True North Consulting
Heat Exchanger Programs
Office:856-391-3347
479-280-9072

www.tnorthconsulting.com

fdt@tnorthconsulting.com
ijj@tnorthconsulting.com
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