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Fr7AE Gas TurbinesDry Low-NOx Combustion System
Operating Challenges in O&G Plants
Atul W. Deshpande RasGasLuis A. Rojas RasGas
V. Venkatachallam RasGasMustapha Chelghoum RasGas
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Executive Summary:
After a planned Shutdown and transfer valvereplacement, Propane unit -GT Fr7AE DLN1-started;
Unit failed to transfer to pre-mix steady stateMode (PMSS) and Trip.
05 Days of online troubleshooting using FishboneDiagram, to determine why the unit couldn
tsustain on PMSS mode after several transfers.
Visual inspection of the internal Combustionsystem reveal hardware damages.
RCFA-PROACT Methodology used to investigateand find the causes of the damages.
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Why DLN1 system on Gas Turbine andHow it works during Startup?
The DLN-1 for FR7AE GT meet Qatar Ministry of environment (MOE)in terms of emission norms (NOx < 25 ppm).
Axial AirCompressor
Airinlet
PowerTurbine
Purge AirFlangeConnection toPurge Valves
Vent
PurgeValve-1
PurgeValve-2
VGC-3
FUELGAS
SRV
VGC-2
VGC-1
PrimaryFuelManifold
Transfer/ PurgeManifold
Secondar y FuelManifold
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Fishbone Diagram for Online Troubleshooting
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Combustion Inspection Findings
Carbone DepositsOn Primary andSecondary Nozzles
ThermalDamage
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Combustion Inspection Findings:Combustion Liner No 5: Major damage
Liner #5 CrackedCircumferentially
Material MeltedDown Insidethe Liners.
Liners LateralCracks
Liner CapsDeformation
Loss of Material
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Combustion Inspection Findings:Combustion Liner No 4: Major damage
Liner #4 CrackedCircumferentially
Missing PieceNear Hula Seal Cracks and
LateralMovement
3 Liner CapsDeformedDownward
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Root Cause Failure Analysis RCFAEvent Diagram:
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Investigations..1Control System Trends.
Fuel gas Pressure Fluctuations before the event
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Investigations ..2Control System Event Trends during transfer
Spike in Compressor Pressure &Exhaust temperature
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Investigations..3Purge Air Connection on Wrapper
Side View of Wrapper
Purge AirConnectionTo Wrapper
2
4
3
5
EndView
Gas
Air
Liner DamageArea
Purge Air Connection on Wrapper Close to combustion can #4&5
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Investigations..4Purge Valve installation
Same SAP number Normally closeactuator & Normally Open actuator
Ball closes opposite toseat leaving wide gap
in closed condition
Closing opposite to seat/Incorrect SAP material number
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Investigations..5Fuel Gas System.
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Selexol draineddaily
53 - C010
SELEXOL Absorber
LC
53 - V010
SELEXOL KO DRUM
Unit 53 Battery Limit
93 - V121
FG MIXING DRUM
EFG FFF
93 - E122
~50 C
~42 C
FG scrubber& strainer skid
56 - Y004
FG Valve Skid(56 - Y002)
Gas Turbine (56 - KT004)
FG scrubber& strainer skid
56 - Y003
FG Valve Skid(56 - Y001)
Gas Turbine (56 - KT001)
LeanSELEXOL
solvent
Rich
LC LC
53 - V010
SELEXOL KO DRUM
Unit 53 Battery Limit
93 - V121
FG MIXING DRUM
EFG FFF
93 - E122
~50 C
~42 C
FG Filters 56 - Y004
FG Valve Skid(56 - Y002)
Gas Turbine (56 - KT004)
FG Filters
56 - Y003
FG Valve Skid(56 - Y001)
Gas Turbine (56 - KT001)
LeanSELEXOL
solvent
RichSELEXOL
solvent
Regen gas fromdehydration unit
(Unit 53)
FFF (duringstartup)
~65 C
~48 kNm3/hr
Excess gas to fuelgas header
~15 kNm3/hr
~15 kNm3/hr
Sour Gas Flare
Fuel gas strainer
Filters Specification 0.3m for solid &
liquid removal, existing 3m for solidonly .
Mixing drum not a knock outdrum (no demister) Upstream demisters noteffective
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RCFALogic Tree (1)
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Hardware damagedue to uncontrolled
combustion
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RCFALogic Tree (suite)
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Main Cause:Backflow of Fuel gas
through purge lineContributing Fact:
Liquid accumulation due toinadequate Filtration and
piping lay out
Main Cause:Backflow of Fuel gas
through purge line
Main Cause:Backflow of Fuel gas
through purge lineContributing Fact:
Liquid accumulation due toinadequate Filtration and
piping lay out
Contributing Fact:Liquid accumulation due to
inadequate Filtration andpiping lay out
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RCFARecommendations
Work Management:
Change SAP material code for the purge valve actuator. Develop Purge Valve Installation Procedure. Time based purge valve replacement.
Engineering Design:
Upgrade purge valves, actuators, solenoid. DLN mode transfer software modification. Upgrade fuel gas filtration system & DLN valve skid layout. Upgrade demisters of Selexol Absorber & mixing drum. Install Combustion Dynamics Monitoring system for allFrame 7 DLN Gas turbines.
All recommendations have been implemented.
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Questions?
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