TL;DR
High combustion dynamics come from fuel-air ratio instability in the combustion can. Verify fuel nozzle pilot split, check for blocked nozzles, and compare fuel heating value to the turbine control system's expected value.
What you might see
- combustion dynamics pressure amplitude above alarm threshold
- increased combustor liner and transition piece wear rate
- audible rumbling from the turbine enclosure
- DCS alarm for high combustion dynamics on one or more cans
Likely causes
Fuel heating value deviation from the control system calibration point causing lean blow-out oscillations
Blocked or worn fuel nozzle creating a lean zone in one combustion can
Combustor liner damage altering the acoustic properties of the can
Pilot fuel split set outside the recommended operating window for the current load and ambient
Required tools
- DCS combustion dynamics monitoring screen
- Fuel gas chromatograph or heating value analyzer
- Borescope
Safety first
- Never adjust fuel pilot split outside the OEM-specified range. Aggressive changes risk flameout or hot-section over-temperature.
- All combustor hardware inspections require the turbine to be offline, cooled, and locked out.
Procedure
- 1
Identify which combustion cans have the highest dynamics readings from the DCS dynamics monitoring system.[1]
- 2
Check the fuel gas composition and heating value against the turbine control system's reference value. Heating value deviations above 2% from the calibrated value can shift combustion stability.
- 3
Verify pilot fuel split parameters in the control system are within the OEM's recommended range for the current ambient temperature and load.
Warning: Do not make fuel split adjustments beyond the OEM-approved trim range without OEM engineering review. Incorrect adjustments can create flameout or over-temperature conditions. - 4
At the next available outage, borescope the highest-dynamics cans for liner cracking, worn premix swirlers, or nozzle damage.
- 5
Inspect and flow-test the fuel nozzles from the highest-dynamics cans for plugging or wear.
- 6
Replace any cracked liner sections or damaged transition pieces per the OEM's run/repair limits.
- 7
After repairs, re-run the turbine and verify dynamics readings have returned to the normal operating range.
Sources
GE Vernova GE 7HA.02 / 7F.05 Gas Turbine (Heavy / Aero) general technical documentation, GE Vernova
Gas turbine combustion dynamics management, fuel-air ratio control, general power generation references (general)
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