GAS TURBINE

PRINCIPLE :-- Fluid is drawn into the compressor and after compression passes to a combustion chamber. Energy is supplied in the combustion chamber by spraying fuel into the fluid stream, and the resulting hot gases expand through turbine. In our case working fluid is atmospheric air.

Gas turbine operates on the principle of Brayton cycle.

TURBINE

COMPRESSOR

COMBUSTIONCHAMBER

COOLING

TEMP

ENTROPY

PRESSURE

VOLUME

COMBUSTIONCHAMBER

TURBINECOMPRESSOR

COOLING

BRAYTON CYCLE

1

2 3

4

1

2

3

4

CC

GD

AIRIN

D-DIESEL ENGINECC-COMBUSTION CHEMBERG-GENERATOR

TURBINECOMPRESSOR

FUEL

EXHAUST

GAS TURBINE

BLOCK DIAGRAM OF GAS TURBINE

DIESELENGINE

ACC.GEAR

MAINCOMP.

TURBINE

BOOSTERCOMPRESSOR

TORQUE CONVERTOR RATCHET

JAWCLUTCH

ATOM.AIRCOMP.

FUELPUMP

MOP MHOP

AIR FILTERFUEL

COMBUSTION CHAMBER

GENERATOR EXITOR

BYPASSSTACK

DIVERTOR DAMPER

HRSG

FUNCTIONS OF VARIOUS MAJOR COMPONENTS

DIESEL ENGINE: --- It is required to supply a high torque at the time of starting to drive the turbine upto the firing speed and then fire turbine to reach self sustaining speed. It also drives the start up compressor till the main compressor comes into the service.

TORQUE CONVERTOR:--- It is used to provide the required torque and speed for the

cranking of the turbine.

RATCHET:---- The ratcheting system is provided for rotating the shaft either before

start up or after the shutdown of the machine.

JAW CLUTCH:--- The function of jaw clutch is to engage/disengage diesel engine to gas turbine.

ACCESSORY GEAR BOX:----

Accessory gear box performs the following multiple functions.

1) To drive the various accessories at their designed speed and required

torque.

2) To connect and disconnect the tubine from the starting device.

3) To trip the turbine mechanically through over speed bolt mechanism.

VARIOUS COMPONENT DRIVEN BY ACCESSORY GEAR BOX ARE.

A) Main Hydraulic Oil Pump (MHOP).

B) Main Lube Oil Pump (MOP).

C) Main Atomising Air Compressor.

D) Fuel Oil Pump.

AIR INLET SYSTEM:---- It is required to provide clean air to the compressor from the atmosphere. The atmospheric air passes through a set of filter element and then to the inlet plenum of the main air

compressor.

MAIN AIR COMPRESSOR:--- Compressor is axial flow type with 17 stages. The compressor suction recieves clean air from the air

inlet system. The compressed air is used in GT for

the various purposes as described below.

A) Combustion of fuel in combustion chamber.

B) Cooling of various turbine parts.

C) Sealing of oil in bearings.

D) Purging of air filters.

INLET GUIDE VANES(IGV):---It is located at the after end of inlet casing. The position of these vanes controls the quantity of

compressed air flow. Vanes are actuated by a

hydraulic cylinder connected to the control ring

that turn the individual pinion gears mounted at

the end of each vane.

COMBUSTION SECTION:--- The combustion system is reverse flow type. The high

pressure air from the compressor reverses its path in the

transition pieces and then move to the annular spaces

that surround each of ten combustion chambers.

EACH COMBUSTION CHAMBER HAS THE FOLLOWING MAIN PARTS:----

a) Nozzle Flow Sleeve

b) Liner

c) Transition Piece

d) Cross Fire Tube

e) Spark Plug (2 nos.)

f) Flame Detectors(2nos.)

FUNCTIONSOF VARIOUS PARTS

A) TRANSITION PIECES:--- It directs the hot gases from the liner to turbine nozzle.

B) NOZZLE:--- It disperses and mixes the fuel with proper amount of combustion air.

C) CROSS FIRE TUBE:--- A passage to propagate the flame from one combustion

chamber to another after the initiation of fire by spark plug.

D) COOLING OF LINER WALL:--- A film of main compressor discharges air shields

the liner wall from the hot combustion gases.

E) COMBUSTION CHAMBER:--- In the combustion chamber, hot combustion gases

from the reaction zone passes to the dilution zone where additional amount of air is mixed to bring the temp. of hot gases to desired level.

F) SPARK PLUG:--- Combustion is initiated by the spark plugs provided in two

combustion chambers when the firing command is given by the

Mark - V. The spark plug operates at the voltage of 11 KV & this high voltage is supplied by ignition transformer.

G) ULTRA VIOLET FLAME DETECTOR:---During the starting sequence, it is essential that indication of

presence or absence of flame in the combustion chambers be transmitted to the Mark-V. The two nos. flame detectors are

provided in combustion chamber no. 7 & 8 to meet the purpose.

H) FUEL NOZZLES:--- Each combustion chamber has one nozzle & each nozzle has four

inlets for Natural Gas, liquid fuel, Purge air & atomising air. The liquid is atomised by means of atomising air. The swirl tip in the nozzle imparts a swirl in the combustion air for complete combustion and resulting in the smoke free operation of the

unit.

TURBINE:--- The turbine has two stages. Turbine section is the area in which heat

heat energy in the form of pressurised hot gases produced by the

compressor and combustion sections is converted into the mechanical

energy. The main parts and features of turbine are described below.

A) COOLING OF BUCKETS:--- As the first stage bucket are the first to encounter the extremely hot gases, hence longitudinal holes are provided in these buckets for cooling as air is passes through holes.

B) TURBINE ROTOR COOLING:--- Rotor cooling is done by means of a positive flow of cool air radially outward through a space between the wheel and the buckets, then

through the stator and finally in to the main gas stream area which is called wheel space.

C) FIRST STAGE WHEEL SPACE COOLING:--- The forward wheel space cooling is done by compressor discharge air which is leaking through the labyrinth. This air discharges in to the main gas stream. The aft wheel space is cooled by 2nd stage nozzle cooling air.

D) SECOND STAGE WITH SPACE COOLING:--- Forward wheel space is cooled by leakage from Ist stage aft wheel

space through the inter stage labyrinth. Aft wheel space is cooled by air from the internal extraction system. This air enters the wheel space through slots in the forward face of the spacer.

SPECIFICATION OF GAS TURBINE AIR COMPRESS0R

1. NO OF STAGES : 17

2. TYPE : AXIAL FLOW

3. CASING SPLIT : HORIZONTAL

4. COMPRESSION RATIO : 1:10.3

5. RATED SPEED : 5100 RPM

6. EXTRACTION : 4th, 10th & 17th STAGE FOR COOLING,

SEALING & AIR FILTER, PULSE CLEANIG.

TURBINE

1. NO OF STAGES : 2

2. TYPE : IMPULSE

3. CASING SPLIT : HORIZONTAL

4. MINIMUM CONTINUOUS

SPEED : 4896 RPM

5. IGNITION SPEED : 940 RPM

6. SELF SUSTAING SPEED : 2640 RPM

7. MECHANICAL TRIP SPEED : 5737 ± 50

8. ELECTRICAL TRIP SPEED : 5610 +30

COMBUSTION SYSTEM

1. TYPE : REVERSE FLOW

2. NO OF COMBUSTER : 10

3. NO OF FUEL NOZZLE/

COMBUSTERS : 1

4. TYPE OF IGNITORS : AUTOMATIC RETRACTING TYPE

5. NO OF IGNITORS : 2

6. NO OF FLAME DETECTORS : 2

7. TYPE OF FLAME DETECTORS : ULTRA VIOLATE

8. FIRING TEMP. AT BASE LOAD : 963°C AT TRAILING EDGE OF 1st

STAGE NOZZLE.

9. FIRING TEMP. AT PEAK LOAD : 996°C.

ISO OUTPUT WITH NG : 26.3 MW

IS0 OUTPUT WITH DISTILLATE : 25.8 MW

HSD & NAPTHA : FUEL FOR GT & HRGS.

HEAT RATE WITH NG : 3021.5 KCAL/KWH

HEAT RATE WITH DISTILLATE : 3041.5 KCAL/KWH

USED HEAT ENERGY

REJECTED

ENTROPY CHART

HEAT ENERGY

ENTROPY

TEMPERATURE

EFFECT OF INCREASED

BACK PRESSURE

EFFECT OF INCREASED

BACK PRESSURE

USED HEAT

ENERGY

REJECTEDHEAT ENERGY

TEMPERATURE

ENTROPY

EFFECT OF INCREASED STEAM

TEMPERATURE & PRESSURE

TEMPERATURE

ENTROPY

USED HEAT

ENERGY

REJECTED

HEAT ENERGY

EFFECT OF REHEAT ON

CYCLE EFFICIENCY

TEMPERATURE

ENTROPY

USED

HEAT ENERGY

ADDITIONAL HEAT

INPUT IN THE REHEATER

REJECTED

HEAT ENERGY

TEMPERATURE

ENTROPY

1

2

3

4

GAS TURBINE CYCLE

USED HEAT

ENERGY

REJECTED HEAT ENERGY

TEMPERATURE

ENTROPY

1

2

3

4

USED HEAT

ENERGY

REJECTED HEAT ENERGY

GAS TURBINE & HRSG

COMBINE CYCLE

SLN0 GAS TURBINE STEAM TURBINE

1 EFFICIENCY SIMPLE CYCLE = 29% TURBINE CYCLE=30%

CO-GENERATION= 85%

2 GESTATION PERIOD LOW(18 MONTHS) HIGH (30 MONTHS)

3 LIFE AROUND 10 YRS. THEN 20 TO 25 YRS.

REQUIRES MAJOR MAINT.

4 MAINTENANCE COST HIGH LOW

5 OPERATION COST LOW HIGH

6 STARTING TIME LESS( 12 TO 15 MIN) MORE ( 1 TO 2 HRS. )

7 GOVERNOR MICROPROCESSOR BASED HYDRAULIC

8 AUXILIARIES/UTILITY LOW HIGH

9 EMISSION ( Nox, Sox ) LOW HIGH

COMPARISON OF GT & STG

GAS TURBINE TRIPPING PARAMETERS UNITS

1 LUBE OIL HEADER PRESSURE LOW 0.7 kg/cm2

2 LUBE OIL HEADER TEMPERATURE HIGH 78 degree C

3 BEARING VIBRATION HIGH 25.4 mm/sec

4 EXHAUST GAS TEMPERATURE HIGH TTRBXB + 22

5 EXHAUST DUCT PRESSURE HIGH 12" WC

6 INLET DUCT PRESSURE 8" WC

7 FUEL GAS PRESSURE LOW 13 bar

8 TURBINE OVERSPEED 110%

9 TRIP OIL PRESSURE LOW 1.3 kg/cm2

10 FLAME FAILURE

11 LOSS OF FUEL

P