GE Vernova GER-3620 Operating and Maintenance

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Doc Name : GER-3620 Rev P Released Date : 2021/03/15 Page 20 of 60
guaranteed emissions, which is the premixed combustion
mode (PM). This combustion mode is also the most beneficial
operation mode for ensuring expected hardware life.
Continuous and extended mode operation in non-PM
combustion modes is not recommended due to reduction in
combustion hardware life as shown in Figure 24.
The use of non-emissions compliant combustion modes can
affect the factored maintenance intervals of combustion
hardware as shown below:
•
DLN-1/DLN-1+ extended lean-lean operation results
in a maintenance factor of 10. Nimonic 263 will have a
maintenance factor of 4.
•
DLN 2.0/DLN 2+ extended piloted premixed operation
results in a maintenance factor of 10.
•
Continuous mode operation in Lean-Lean (L-L), sub-
Piloted Premixed (sPPM), or Piloted Premixed (PPM)
modes is not recommended as it will accelerate
combustion hardware degradation.
•
In addition, cyclic operation between piloted premixed and
premixed modes leads to thermal loads on the combustion
liner and transition piece similar to the loads encountered
during the startup/shutdown cycle.
Another factor that can affect combustion system
maintenance is acoustic dynamics. Acoustic dynamics
are pressure oscillations generated by the combustion
process within the combustion chambers, which when
are present at high levels can lead to significant wear of
combustion or hot gas path components. Common GE
Vernova practice is to tune the combustion system to
levels of acoustic dynamics deemed low enough not to
affect life of gas turbine hardware. In addition, GE Vernova
encourages monitoring of combustion dynamics during
turbine operation throughout the full range of ambient
temperatures and loads.
Combustion disassembly is performed, during scheduled
combustion inspections (CI). Inspection interval
guidelines are included in Figure 36. It is expected, and
recommended, that intervals be modified based on specific
experience. Replacement intervals are usually defined
by a recommended number of combustion (or repair)
intervals and are usually combustion component specific.
In general, the replacement interval as a function of the
number of combustion inspection intervals is reduced if the
combustion inspection interval is extended. For example, a
component having an 8,000-hour CI interval, and a
16
six CI replacement interval, would have a replacement
interval of four CI intervals if the inspection intervals were
increased to 12,000 hours (to maintain a 48,000-hour
replacement interval).
For combustion parts, the baseline operating conditions
that result in a maintenance factor of one are fired startup
and shutdown to base load on natural gas fuel without
steam or water injection. Factors that increase the hours-
based maintenance factor include peak load operation,
distillate or heavy fuels, and steam or water injection.
Factors that increase starts-based maintenance factor
include peak load start/stop cycles, distillate or heavy fuels,
steam or water injection, trips, and peaking-fast starts.
Casing Parts
Most GE Vernova gas turbines have inlet, compressor,
compressor discharge, and turbine cases in addition to
exhaust frames. Inner barrels are typically attached to the
compressor discharge case. These cases provide the primary
support for the bearings, rotor, and gas path hardware.
The exterior of all casings should be visually inspected for
cracking, loose hardware, and casing slippage at each
combustion, hot gas path, and major outage. The interior
of all casings should be inspected whenever possible. The
level of the outage determines which casing interiors are
accessible for visual inspection. Borescope inspections are
recommended for the inlet cases, compressor cases, and
compressor discharge cases during gas path borescope
inspections. All interior case surfaces should be inspected
visually, digitally, or by borescope during a major outage.
Key inspection areas for casings are listed below.
•
Bolt holes
•
•
•
Shroud pin and borescope holes in the turbine shell (case)
Compressor stator hooks
Turbine shell shroud hooks
•
•
Compressor discharge case struts
Inner barrel and inner barrel bolts
•
•
•
Inlet case bearing surfaces and hooks
Inlet case and exhaust frame gibs and trunions
Extraction manifolds (for foreign objects)
Exhaust Diffuser Parts
GE Vernova exhaust diffusers come in either axial or radial
configurations as shown in Figures 25 and 26 below. Both
types of diffusers are composed of a forward and aft
section. Forward diffusers are normally axial diffusers,
Non-Public- Class II (Non Critical) - NLR