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Gas TurbinePrepared by: Ayaz Ahmed

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CONTENTS INTRODUCTION OPERATION PRINCIPAL & THERMODYNAMIC CYCLE INTRODUCTION TO GE GAS TURBINES AT FATIMA LAYOUT OF TURBINE & GENERATOR MAIN COMPONENTS & THEIR WORKING

STARTING EQUIPMENT AIR INLET EQUIPMENT AIR COMPRESSOR VARIABLE INLET GUIDE VANES COMBUSTION SECTION TURBINE EXHAUST SECTION GENERATOR

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TURBINE AUXILARY SYSTEMS & THEIR WORKING GAS FUEL SYSTEM LUBE OIL/ HYDRAULIC OIL SYSTEM COOLING & SEALING AIR SYSTEM ATOMIZING AIR SYSTEM COOLING WTER SYSTEM

FACTORS AFFECTING PERFORMANCE OF GAS TURBINE

OPERATION PRACTICES & TURBINE MONITORING

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PRIME MOVERS Gas Turbine Steam Turbine I.C. Engine Electric Motor Expansion Turbine

Comparison Thermal efficiency of G.T. ~25- 32% whereas in I.C. Engine ~35-45%. For the same power output, larger size Engine required as compared to

G.T. Maintenance cost at I.C. Engine is much higher than G.T. Thermal efficiency of Steam Turbine ~70-80 %. Steam turbine requires installation of Boiler, condenser, pumps etc. so

initial capital investment becomes higher. Motors becomes un-economical at higher power output because of

in-efficient conversion of energy into electric power. Expansion Turbines used to recover waste energy from process. These

supplement the main prime mover.

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GAS TURBINE APPLICATIONS Gas Turbine developments in early nineties. G. T. available in wide power range ( 7 KW-300 MW )

Applications. Stationary applications

As a Prime mover for; Compressors Large Pumps Electric Generators

Mobile Applications Aircraft field Marine propulsion

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GAS TURBINE OPERATING PRINCIPLE Conversion of Chemical Energy of fuel to Mechanical

Energy. Air Compressor/Turbine mounted on single shaft are brought to

speed by diesel engine. Air Compressor draws atmospheric air & increases its pressure. High pressure air flows to combustion chamber where fuel

admitted under pressure. Spark ignites fuel/air mixture initially. Hot gases at high pressure expand thru Turbine wheels. Rotor spins and produces shaft output. Part of the shaft output is used internally by air compressor, the

remaining output available for driven unit. Gas Turbine Flow Diagram

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G E TURBINES AT FATIMA (O&U Plant) No. of Gas turbine Units at Fatima : 02 Gas Turbine make : General Electric

Data Summary

Gas Turbine model series : MS-5001 PA: Single Shaft Unit

Gas Turbine application : Generator Drive Base out put : 26.3 MW Operation cycle : Simple Shaft speed : 5100 rpm Air inlet temp. : 43°C Exhaust temp. (On Gas fuel) : 507 °C Atmospheric Pressure : 0.99 bar

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Compressor Section Compressor type : Axial Flow (Horizontal Split

Casing) No. of compressor stages : 17 Inlet Guide Vanes : Variable Pressure Ratio : 10.5 : 1

Turbine Section No. of Turbine Stages : 2

Combustion Section Combustors : 10 ( multiple combustors, reverse flow design) Chamber Arrangement : Concentrically (located

around the compressor)

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Fuel nozzle : Pressure atomizing 1 per chamber Spark plugs : 02, Electrical type, spring injected,

self retracting Flame detectors : 04, ultra-violet type

Starting system Starting device : Diesel Engine

Reduction Gear Shaft speed ratio : 5100/1500 rpm

Generator Type : air cooled open ventilate Rating : 26,250 kVA, at p.f. 0,80 Rpm : 1500 Volts : 11000 volts Frequency : 50 Hz.

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LAYOUT OF TURBINE & GENERATOR

EXHAUST PLENUM

TURBINE COMPARTMENT

AIR INLET

PLENUMACCESSORY COMPARTMENT

LOAD GEAR COUPLING

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MAIN COMPONENTS & THEIR WORKING

STARTING EQUIPMENT Diesel Engine make : DEUTZ (TYPE: TBB 616 V8) Engine Power : 450 KW Engine rpm : 2100 Cranking or rotation of Gas turbine Shaft By Diesel Engine. Diesel Engine transmits rotating speed through torque converter

& Jaw clutch to accessory gear. Main functions of Starting Device

Supply high torque at zero speed to breakaway the turbine. Drive the unfired Gas Turbine to Firing Speed (18% or 1000 rpm) Assist the Fired Gas turbine to self sustaining speed after which

starting device is declutched from Gas Turbine.

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STARTING SYSTEM COMPONENTS Diesel Engine Hydraulic torque converter Assembly Hydraulic Ratchet system Starting Jaw clutch

ENGINE OPERATION With start signal , Ratchet Pump starts , Starting Clutch

engaged, & Diesel Engine starting DC motor energized. Engine at idle speed (600 rpm) for two minutes warm up period.

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At the end of warm-up period, Engine governor set at maximum

speed (2100 rpm) until Turbine shaft starts rotation.

Engine speed set between idle & maximum ( 1800 rpm , governor

speed).

Turbine correct firing speed (1000 rpm of Turbine shaft) is

achieved. Engine speed remains at 1800 rpm while Gas Turbine

warm-up period is completed.

At 50% of unit speed (2800-2900rpm) Gas Turbine becomes self

sustaining & overtakes diesel Engine. Diesel Engine returns to

idle speed & idles for 05 minutes cool down period & then stops.

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RATCHETINGRatcheting is slow turning of gas turbine shaft. Ratcheting Required:

During the cool down period of gas turbine to avoid Shaft BOW. During the start-up to help diesel Engine for Gas turbine’s shaft

break away from zero speed. In ratcheting Turbine shaft rotates 47 degrees in 10 seconds after

every 03 minutes. A small DC-motor (125V) rotates the shaft through Hydraulic self

sequencing valve assembly. Ratchet mechanism de-energized when the G.T shaft break-away

achieved.

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AIR INLET EQUIPMENT (Filter House) Gas turbine kind of air breathing machine. Design consumption of Air at our Gas turbine is 103 kg/sec at

430C & 0.983 bar corresponding Air/fuel ratio of 40. Performance of Gas turbine very sensitive to the quality of

Air & affected through: Fouling of compressor Blades Erosion of compressor/Turbine Blades

Fouling reduces the efficiency of the axial compressor by ingestion of substances which adhere to surface e.g., oil vapors & smoke.

Erosion results due to hard particles in air such as sand & mineral dust etc. These particles when hit on the blades, cut away as small portion of metal thus causing serious damage to machine.

Filtration of Air upto 10 micron size before entering axial compressor.

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Filter House consists of three stage filter assembly: Inlet screens & Inertial separators Pre-Filters (Primary Filters) High Efficiency filters (secondary filters)

Inlet screens Screens/weather hoods at upstream of inertial separators to avoid

entry of birds, leaves, twigs papers etc. Pre-Filters (Primary Filters)

Pre-filters can be installed immediately upstream of high efficiency filters.

Pre-filters extend the useful life of high efficiency filters. These are layer type & directly attached to high efficiency filters. Generally replaced when P across the filter house reaches 12 cm wc.

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High Efficiency Filters (Secondary Filters) Made with special paper fabric & have efficiency of 99.7% particles removal. Large particles remove by sieve-like action where as smaller ones adhere to

fabric. Normal life is about 6 months. Inlet ducting & silencing

An air inlet duct connects the Filter House to air inlet plenum at compressor suction.

Silencing provided in the duct by the use of acoustically perforated sheets. Silencing baffles eliminate typical compressor tone.

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AIR COMPRESSOR 17 stage axial compressor with inlet variable guide vanes. Compressed air exits through compressor discharge casing to the

combustion chambers. Air also extracted from the compressor for turbine cooling & bearing oil

sealing. Compressor divided into four portions:

Inlet section Forward section Aft section Discharge section

FIG. (Comp/Turbine Rotor assembly) FIG. (Compressor Casing Lower half)

Inlet section The inlet section directs air flow from Filter House into compressor blading. This section contains variable inlet guide vanes assembly, the No. 1

bearing assembly & Low pressure air seals. Variable inlet guide vanes (IGV) permit fast, smooth acceleration of Gas

turbine without compressor surge.

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IGV operated through hydraulic system & rotate through a large ring gear &

multiple small pinion gears. At start up of Gas turbine IGV’s are set at 43̊ position & when Turbine

accelerates to 95% speed they turn to 85̊ position. When turbine stops vanes rotated to 43̊ at once.

FIG. (Guide Vanes Pinion gear ring) Aft Section

This is at down stream of inlet section & contains the stator Blading for stages 4 through 9.

Bleed air from the 4th rotor stage (between 3rd & 4th stator stage) used for cooling of turbine shell & supports.

Discharge Section This section down stream of the aft section, contains the stator blading for

the stages 10 through 16 & exit guide vanes stages 1& 2. This section provides the mounting surface for combustion chambers.

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COMBUSTION SECTION Components of Combustion section

Combustion chambers Fuel Nozzles Spark plugs Flame detectors Transition pieces

Combustion Chambers (Diagrams) Ten combustion chambers arranged concentrically around the axial flow

compressor & bolted to compressor discharge section bulkhead. Combustion Air supplied directly from the discharge of axial flow

compressor to combustion chambers. Fuel fed into the chamber through the fuel nozzles that extend into each

chamber’s liner cap. Combustion chamber outer casing bolted to compressor discharge. Combustion takes place in inner liner. Chambers called as reverse flow type.

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Spark Plugs Combustion of fuel & air mixture initialed by spark plugs. Spark plugs installed in two of combustion chambers & receive

power from the ignition transformers. The chambers without spark plugs (08 chambers) fired with flame

from the fired chambers through interconnected cross-fired tubes. Flame Detectors

Four ultra-violet type flame detectors provided on the combustion chambers opposite to those having spark-plugs.

They detect the presence of ultra-violet radiation which is emitted by a hydrocarbon flame. The detectors provide a signal when the radiation is sensed for approx. 0.2 sec.

On failure of both flame detectors Gas Turbine trips. Flame sight ports on individual chambers. Flame detectors ensure combustion in other 08 chambers thru

cross-fired tubes.

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TURBINE SECTION High temperature gases from combustion section converted to shaft

horsepower. Power required to drive load package & compressor provided by the two-

stage turbine rotor. Turbine components

First stage nozzles First stage Buckets & wheel Second stage nozzles Second stage Buckets & wheel

FIG. (1st & 2nd Stage Wheels & Nozzles) Combustion gases at about 800 °C expand through two stages of

Turbine. Expansion takes place in fixed nozzles of both stages. Nozzles convert heat & pressure energy into high velocity or kinetic

energy and direct this energy to buckets/rotating blades. Rotating blades convert kinetic energy into useful shaft horse power.

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Temperature limitation on turbine wheels due to metallurgy. Cooling of turbine parts (stationery nozzles, rotary blades, turbine shaft

& supports) with air drawn through compressor from different stages. Turbine’s 1st Stage buckets are hollow & have cooling holes in the

buckets. Cooling of wheel space area with compressor air. Use of seals between nozzles & rotating buckets to restrict the hot gases

from leaking into the wheel space. Operation of turbine with excessive wheel space temperatures can cause

failure of rotor studs connecting the turbine wheels. Exhaust Section

Turbine exhaust gases discharged thru diffuser into the exhaust plenum at temperature of about 507̊ C.

FIG. (Turbine Wheels, Exhaust Hood & Deflector)

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Generator Principle

Conversion of mechanical energy into electrical energy. When magnetic field is cut by conductor, voltage is

produced in the conductor.The higher the strength of magnetic field, the higher would be the voltage produced in the conductor.

Generator having two parts: 1. Stator 2. Rotor Stator has 3-phase armature winding (stamping insulated with

paper) In star connection. Rotor contains field winding which develops electromagnet. Field excitation (Rotor magnetization) initially obtained thru

battery & then thru Static Excitation System.

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Fuel Gas System Gas Stop/Speed ratio valve (SRV) This valve is operated thru hydraulic cylinder & has two functions; Stop Function

Tight shut-off of fuel gas achieved by hydraulic oil drainage thru SOV (20FG).

Speed ratio Function Regulated inlet pressure to upstream of control valve. Pressure at downstream of stop/speed ratio valve maintained at 14.0

kg/cm.2 Electro-hydraulic servo ( 90 SR ) gives position control. Input to electro-hydraulic servo ( 90 SR ) is the speed signal & downstream

pressure signal ( 96 FG ). Actual position of valve sensed thru LVDT (liner variable differential

transformer,96 SR ). LVDT installed on stem provides feedback signal to speedtronic.

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Gas Control Valve (GCV) Gas control valve provides the final precise metering of fuel gas flow to gas

turbine. It regulates gas pressure of 8-10kg/cm2 to fuel nozzles. Speed tronic control gives its output signal called VCE to the electro-hydraulic

servo (65 GC). This servo adjusts the hydraulic pressure to the piston of gas control valve.

Two LVDT’s (96 GC-1/2) provided at the stem of gas control valve give position feedback to the speed tronic control.

VCE signal by the control circuit is compared with the position feed back signal by LVDT’s. If the two signals do not match an “error” signal is generated and acts to reposition the valve until the VCE & feed back signals match.

Fuel Gas Vent valve (20 VG) Solenoid operated valve (20 VG) vents the gas from the piping in-between gas

stop/speed ratio valve & Gas control valve. This solenoid is energized & vent valve closes when start signal is given to turbine,

it will remain closed until turbine is shutdown. It provides block-n-bleed arrangement while gas turbine is shutdown.

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LUBE OIL / HYDRAULIC OIL SYSTEM Closed loop forced oil lubrication system.

Lube oil Tank Integral part of the turbine base in the area under accessory section. Capacity of the system (tank & other components) is 9000 litres. Lube oil feed piping is contained within the lube oil tank or drain headers

to avoid safety risk in case of leakage. Three lube oil pumps

The main lube oil pump is positive displacement type mounted in & driven by accessory gear.

The auxiliary lube oil pump is a submerged centrifugal pump driven by 380V AC motor.

The emergency lube oil pump is a submerged centrifugal pump driven by 110 V DC motor.

Lube Oil Securities High lube Oil Temperature alarm at 75 °C High lube Oil Temperature Trip of turbine at 80 °C

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Cooling & Sealing Air System Different Turbine parts to be cooled;

First & second stage turbine wheel forward & aft faces. First & second stage nozzles Turbine shell Turbine supports Combustor’s casing , liners, transition Pieces.

Cooling air obtained from the compressor at following locations; Fourth stage Extraction Air. Tenth Stage Extraction Air. Compressor High Pressure Seal Leakage. Compressor Discharge Air.

FIG (Schematic cooling sealing air)

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Fourth stage extraction air Portion of shell surrounding the first & second stage nozzles Aft surface of second stage turbine wheel Supports which are in the exhaust gas hot path

Tenth stage extraction air Main part goes through bleed valves to exhaust plenum Second part for cooling of 1st. & second stage nozzles Third part routed to bearing’s seals through dirt separator

Compressor high pressure seal air leakage Cooling for first stage wheel & discharged to exhaust hot gas path

Compressor discharge air Cooling of aft surface of first stage turbine wheel forward surface

of second stage turbine wheel 1st stage nozzle ring & partitions

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FACTORS AFFECTING PERFORMANCE OF GAS TURBINE

Performance of Gas Turbine affected by: Atmospheric Pressure

With pressure reduction, Specific weight of air reduces which reduces power output.

For the same power output fuel consumption increases. For every 100 mm wc pressure reduction efficiency reduces by ~ 1 %.

Ambient Temperature Increase in ambient temperature also reduces specific weight of air which

reduces power output. For every 10 ̊C increase in ambient temperature efficiency reduces by ~ 1 %.

∆P Across Filter House Increase in ∆P across filter house reduces Turbine efficiency.

Humidity in Air Humid air tends to clog filters & increases ∆P across filters.

Load At higher load Turbine efficiency improves & vice versa.

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Cap cowl assyCross fire tube collar Dilution holes

Spring Hula skirtSecondary/Mixing airLiner stop

Fuel Nozzle inlet

Primary air holes

Louvers

Vortex generator

FUEL NOZZLE Temperature inducedMaterial failure Primary Air Inlet

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1. Crossfire Tube

2. Atomizing Air Inlet Pipe

3. Oil Fuel Inlet Pipe

4. Dual Fuel Nozzle

5. Sighting Port

6. Gas Fuel Inlet Pipe

DUAL FUEL NOZZLE

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B - Atomizing Air

C - Gas Fuel

A - Liquid FuelFuel Nozzle Body

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