1. Feedwater System Reliability Users Group – 2012 Meeting Feedwater Heater Level Optimization

2. Introduction: True North Consulting, LLC Phone (970) 252-1489
Frank Todd – Mgr. Thermal Perf. Group
Phone (856)
Iver Jacobson—Sr. Consulting Engineer
Phone (479) or (479) (cell)
Heat Exchanger Training

3. Terminal Objective
Familiarize the attendee with the importance of feedwater heater level optimization and the associated issues with establishing the best operating level.

4. Enabling Objectives
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.

5. Feedwater Heater Level
Feedwater Heater Optimum Level:
Below active tubes (thermal efficiency)
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.

6. Feedwater Heater Level

7. Feedwater Heater Level
Knee response of DCA to FWH level.

8. Feedwater Heater Level
In conjuction with the degrading DCA, flow velocity in the DC increases due to the two- phase flow, causing vibration damage.

9. Feedwater Heater Level
Two-phase flow and high tube vibration can cause loss of baffle plates and tube failure.

10. Feedwater Heater Level
Why isn’t original FWH level still ok?
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

11. 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).

12. 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.”

13. Feedwater Heater Level
Vendor Generic FWH Example Diagram:
Notice large spacing between steam nozzle and liquid level connection.

14. Feedwater Heater Level
FWH Shell Diagram (actual)
Notice proximity of level connection taps and steam nozzle (i.e. high velocity past level tap)

15. Feedwater Heater Level
Potential indicators level is not optimum?
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.

16. Feedwater Heater Level
I have “symptoms” of needing a level test.
What are my options?
Raise operating level w/o test.
Perform FWH level test(s).
In-house or with fleet and peer support
External contracted support.
Improve conditions (i.e. insulate pipe, tune controllers to address level oscillation)

17. 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.

18. Feedwater Heater Level
FWH level controller devices

19. 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.

20. 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

21. 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.

22. FWH Test Considerations
Always Remember Murphy’s Law!
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!

23. FWH Test Considerations
Not a fun day at the office:

24. FWH Test Considerations
Much faster turbine disassembly with improved lighting and ventilation.

25. 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)

26. 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)

27. 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.)

28. Feedwater Heater Level
Example of FWH Level Values:

29. Feedwater Heater Level
EPRI TR : 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.

30. 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:
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.

31. Feedwater Heater Level
If a breach in the drain cooler shroud exists, its size and location will affect level test results.

32. Feedwater Heater Level
Drain cooler shroud degradation example.

33. Feedwater Heater Level
Loose material in the shell is a “wild card”. Failed shell liners, plates, tubes, tools, etc. may relocate during flow transients.

34. Feedwater Heater Level
Sustained operation with tube leaks is a common cause of sheared tube fragments in the shell.

35. 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.

36. Feedwater Heater Level
Potential Actions/Changes from Level Test:
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

37. Feedwater Heater Level
Portable ultrasonic instruments, such as UE Systems Ultraprobe, can be useful during walkdowns, monitoring, or level tests.

38. Feedwater Heater Level
Summary of FWH Level Optimization:
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.

39. Feedwater Heater Level
Questions / Comments?
Contacts:
Frank Todd Iver Jacobson
Manager Thermal Performance Sr. Consulting Engineer
True North Consulting Heat Exchanger Programs
Office: