Combustion 6FA

COMBUSTION INSPECTION

Gas Turbine

Unit Data

GT Inspection and schedule

Constructional details of Combustion system

DLN 2, an overview

Combustion and bore scope inspection

Combustion Combustion inspectioninspection

Unit Data

Equipment model PG 6101FA Serial Number 810311Rating 70 Mw

(ISO)Speed 5231 rpmFuel Dual fuelComp Pr. Ratio 14.97:1GT inlet air flow 165 m3/s NOx level 25ppm 6FA


Inspection & Inspection Schedule

a) Running Inspections

Recording of operating data Checking of abnormal conditions/leakages.

b) Special inspections

Bore scope Inspection (34 locations in 6FA) Eddy current probe Inspection.

Variable Inlet Guide Vanes Bushing Inspection

c) Shutdown Inspection

Combustion inspection (8000 EOH/ 450 starts) Hot Gas path Inspection (24000 EOH/ 900 starts)

Major Inspection (48000 EOH/ 2400 Starts)

d) ScheduleCombustion inspection

8000 EOH/ 450 starts Hot Gas path Inspection

24000 EOH/ 900 starts Major Inspection

48000 EOH/ 2400 Starts


Gas Turbine Combustion Explosion view

Compressor discharge casing

Comb casing outer

1ST stage Nozzle

1st stage bucket

Transition Piece

1ST stage Bucket

Shroud

3rd stage bucket

2nd stage bucket

Comb Case

Flow sleeve

Comb Liner


DUAL FUEL NOZZLE CROSS SECTION


6 FA


Combustion Explosion view

Compressor discharge casing

1st Stage

nozzle

Comb casing outer

1ST stage Nozzle

1st stage bucket

Transition Piece

1ST stage Bucket

Shroud

3rd stage bucket

2nd stage bucket

Fuel nozzle & cap assembly

Comb Case

Flow sleeve

Comb Liner


TRANSITION PIECE ARRANGEMENT

Impingement cooling holes


Combustion Technology

The regulatory requirements for low emissions from gas turbine power plants have increased during the past 15 years.

Environmental agencies throughout the world are now requiring even lower rates of emissions of NOx and other pollutants from both new and existing gas turbines.

Traditional methods of reducing NOx emissions from combustion turbines (water and steam injection) –having limitation in reduction level.

Evolution of Dry low nox – Having better control in emission

DLN 1DLN 2 (ABAN)DLN2.6DLN 2.6+


Combustion Technology DLN 2

Burning methodology

a) DIFFUSION

While by injecting fuel into combustion air and firing them simultaneously is called Diffusion combustion

b) LEAN PREMIXED COMBUSTION

Burning technology after mixing fuel with air in advance is called premixed combustion, The term of lean combustion is defined as combustion under a lower fuel concentration to equilibrium. Since the fuel concentration is low in a lean premixed combustion, flame temperature cannot become high. Formation of thermal NOx, which is synthesized in large quantities at a high temperature, is accordingly suppressed. However, lean combustion generally has a problem that tends to become unstable.


DLN2 Fuel Gas nozzle manifolding (Combustion Streams)

Primary Gas (Diffusion 4)Secondary

Gas ( Premix 4)

Tertiary Gas (premix 1) Quaternary Gas

(casing premix) typical 15 place



DLN-2 fuel Four Gas streams (four Manifolds) are:

1) Primary Diffusion passages of four of the fuel nozzles are fed from a

common manifold, called the primary,

Primary fuel – Fuel gas entering through the diffusion gas holes in the swirler assembly of each of the outboard four fuel nozzles

2) Secondary The premixed passages of the same four nozzles are fed from

another internal manifold called the secondary.

Secondary fuel – premix fuel gas entering through the gas metering holes in the fuel gas injector spokes of each of the outboard four fuel nozzles turbine.

DLN - 2.0


3) Tertiary

The pre-mixed passages of the remaining nozzle are supplied by the tertiary fuel system; the diffusion passage of that nozzle is always purged with compressor discharge air and passes no fuel.

Tertiary fuel – premix fuel gas delivered by the metering holes in the fuel gas injector spokes of the inboard fuel nozzle.

4) QuaternaryThe quaternary gas fuel delivery system consists of a nozzle arrangement which penetrates the circumference of the combustion can, porting fuel to casing pegs located radially around the casing.

Quaternary Fuel- Quaternary passages, injects a small amount of fuel into the air stream just up-stream from the fuel nozzle swirlers splitter valve is also modulated to hold a constant tertiary flow split.

DLN - 2.0 Combustion Technology DLN 2


Secondary (premix) injector typical, for 4 nozzle

Primary (diffusion) injector Typical for 4 nozzle

Tertiary (premix) injector Typical for 1 nozzle)

Purge air only Tertiary location

Combustion Modes

DLN - 2.0

DLN- 2.0 Fuel nozzle arrangement


Diffusion gas passage

Water injection

Liquid fuel

Atomizing air

Typical Dual Fuel nozzle arrangement (diffusion)



The DLN-2 combustion system can operate in several different modes.

1) PrimaryFuel, only to the primary side of the four fuel nozzles, diffusion flame. Primary mode is used from ignition to 81% corrected speed.

2) Lean-LeanFuel to the primary (diffusion) fuel nozzles and single tertiary (premixing) fuel nozzle. This mode is used from 81% corrected speed to a pre-selected combustion reference temperature. The percentage of primary fuel flow is modulated throughout the range of operation as a function of combustion reference temperature.

If necessary, lean-lean mode can be operated throughout the entire load range of the turbine. Selecting “lean-lean base on” locks out premix operation and enables the machine to be taken to base load in lean-lean


3) Premix TransferTransition state between lean-lean and premix modes. Throughout this mode, the primary and secondary gas control valves modulate to their final position for the next mode. The premix splitter valve is also modulated to hold a constant tertiary flow split.

4) Piloted PremixFuel is directed to the primary, secondary and tertiary fuel nozzles. This mode exists while operating with temperature control off as an intermediate mode between lean-lean and premix mode.

This mode also exists as a default mode out of premix mode and, in the event that premix operating is not desired, piloted premix can be selected and operated to base load. Primary, secondary and tertiary fuel split are constant during this mode of operation.



5) Pre-Mix Steady State (PMSS)Fuel is directed to the secondary, tertiary and quaternary fuel passages and premixed flame exists in the combustor. The minimum load for premixed operation is set by the combustion reference temperature and IGV position. It typically ranges from 50% with inlet bleed heat on to 65% with inlet bleed heat off.

Mode transition from premix steady state, piloted premix or piloted premix to premix steady state, can occur whenever the combustion reference temperature is greater than 2200 F/1204 C. Optimum emissions are generated in premix mode.

6) Tertiary Full Speed No Load (FSNL)This mode is active when operating above approximately 12.5 % and a load rejection is experienced. . The fuel Split are changed and fuel is directed to the tertiary nozzle only. The fuel system remains in this mode for approximately 60 seconds and then transfers to lean-lean mode.



DLN-2.0 Operating Modes, summary

Gas Fuel Operation:

-Primary (Diff-4) - 4 Primary Tips Only, Ignition Through 81% Speed

-Lean-lean (Diff-4 + Tertiary (1-PM) - 81% Speed Thru Approx 30% Load

-Premix Transfer (Diff 4+Secondary (4-PM) +Tertiary (1-PM)

-Piloted Premix (Diff 4 + Secondary + Tertiary) - 30% to Base If Necessary

-Premix Transfer (Diff 4 + Secondary + Tertiary

-Premix Steady State (Secondary + Tertiary + Quaternary) - 45% to Base

- Quaternary Fuel Injection . Upstream of Fuel Nozzles to Control PM Nozzle Pressure Ratio



Combustion Inspection

Combustion System

The overall function of the combustion system is to supply the heat energy to the gas turbine cycle. This is accomplished by burning fuel mixed with compressor discharge air.

The combustion system is of the reverse-flow type with the combustion chambers arranged around the periphery of the compressor discharge casing (Total 6 Combustion cans)


Relatively a small inspection, required to Inspect / change out the below parts.

• Combustion Liners • Flow Sleeves• Combustion End Covers • Purge valves• Fuel Nozzles • Check Valves• End Caps • Spark Plugs• Transition Pieces • Flame Detectors• Cross Fire Tubes • Flex Hoses

These parts require the most frequent attention, as continued operation with a deteriorated combustion system can result in much shortened life of the downstream parts

It is also inherent in the gas turbine design that these parts are the first to require repair or replacement being exposed to very high temperature.

Therefore, the importance of this inspection in the maintenance program must be emphasized.




To be inspected for

• Foreign Objects• Abnormal Wear• Cracking• Liner cooling hole Plugging• TBC Coating Condition• Oxidation/Corrosion/Erosion• Hot Spots/Burning• Missing Hardware• Clearance Limits


1. Compressor and Turbine 2. Combustion liner3. Combustion liner cap cowl 4. Combustion transition pieces5. Transition piece hardware6. Combustion flow sleeve7. Spark Plug8. Fuel nozzle9. Flame scanner10.Compressor rotor vane

inspection 11.Compressor stator vane12.Inlet Guide vane


Bore scope inspection of following can be done without opening any major parts


Combustion Inspection - findings during May 2006 outage-

ABAN Combustion Inspection findings

Fuel nozzle depositCombustion liner cap cowl - old

Combustion liner New and removed

Combustion liner cap cowl - New



Combustion liner damaged Combustion liner cap cowl cracked


Combustion liner cap crackedCombustion liner damaged


Transition piece

Combustion liner – installed new


Pulse air pipe damaged

Pulse air pipe came out from its position

INSPECTION OF VIGV

R AC KR IN G

O U TERSH AFT

SPAC ER

R O O TO F VAN E

X2

X1

X

M ID SPANO F VAN E

TIPO F VAN E

IN LETG U ID EVAN E

TH R U STW ASH ER

IN N ERSTU BBU SH IN G

BU SH IN G SG EAR

R AC K

INLETCASING

G T500030

INNER STUB CLEARANCE MEASURED LESS VALUE



Combustion 6FA

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Transcript of Combustion 6FA