GAS TURBINE (PG-9171E)
CONTENTS PAGE NO1.1 PROCESS DESCRIPTION 02
1.1.1 GENERAL DETAILS 02
1.1.2 GAS TURBNE CRITERIA 02
1.1.3 CAPTIVE POWER PLANT 03
1.1.4 GAS TURBINE COMBINED CYCLE & COGENERATION 03
1.1.5 GAS TURBINE FUNCTIONAL DESCRIPTION 04
1.2 GAS TURBINE CONSTRUCTION FEATURES 05
1.2.1 COMPRESSOR 05
1.2.2 COMBUSTION SYSTEM 08
1.2.3 TURBINE 11
1.2.4 EXHAUST FRAME & DIFFUSER 18
1.3 GAS TURBINE EQUIPMENT DATA 23
1.4 GAS TURBINE CONTROLS 26
1.5 GAS TURBINE OPERATING SYSTEMS 31
1.5.1 LUBE OIL SYSTEM 31
1.5.2 COOLING WATER SYSTEM 36
1.5.3 FUEL OIL SYSTEM 38
1.5.4 ATOMIZING AIR SYSTEM 42
1.5.5 FUEL PURGING SYSTEM ( LIQUID & GAS FUEL) 45
1.5.6 GAS FUEL SYSTEM 47
1.5.7 HYDRAULIC OIL SYSTEM 49
1.5.8 TRIP OIL SYSTEM 50
1.5.9 COOLING & SEALING AIR SYSTEM 51
1.5.10 STARTING SYSTEM 54
1.5.11 FIRE PROTECTION SYSTEM 56
1.5.12 HAZARDOUS GAS DETECTION SYSTEM 58
1.5.13 HEATING & VENTILATION SYSTEM 58
1.5.14 WARREN PUMP & LUBRICATION SYSTEM 59
1.5.15 INLET AIR FILTERATION SYSTEM 60
1.5.16 WATER WASH (ON LINE/OFF LINE) SYSTEM 60
1.6 GAS TURBINE FUELS 63
1.7 START-UP/SHUTDOWN SEQUENCE ON GAS FUEL 71
1.8 START UP SEQUENCE ON LIQUID FUEL 74
1.9 GAS TURBINE INSTRUMENTATION/PROTECTION SYSTEM 79
1.10 GAS TURBINE GENERATOR 84
1.11 GENERATOR PROTECTIONS 89
GAS TURBINE (PG-9171E)
1.1 PROCESS DESCRIPTION :1.1.1 GENERAL DETAILS
Gas Turbine is a Modern Power generating equipment.
It takes the air from atmosphere compresses it to sufficiently high pressure , same pressurized air is then utilized for combustion , which takes place by in combustion chamber by addition of fuel , there by hot combustion products are generated which are expanded in the turbine where Heat energy of hot combustion products is converted in to mechanical energy of shaft which in turn utilized for generating power in Generator.
Compression is carried out by Axial Flow compressor , Heat addition is done by Fuel in combustion chambers , Expansion of hot combustible gases is carried out in Turbine and Burnt Gases are exhausted to atmosphere or utilized for steam generation in GTs. All of these four processes are carried out in Only one Factory assembled Unit which is called Gas Turbine. Drawing shows the Typical Brayton cycle and also shows the components of Gas Turbine. Gas Turbine operates on Brayton Cycle. Brayton cycle is having divided in four segments namely Compression, Heat addition, Expansion and Exhaust.
Process is explained in following diagram on T-S curve.
1.1.2 GAS TURBINE CRITERIA
Gas Turbine had a following advantages
Capital cost is less .
Fewer auxiliaries.
Less erection time.
Less area.
Higher thermal efficiency when operated in combined cycle mode.
Quick start.
Fuel flexibility ( Liquid / Gas )
Very compact system.
Black start facility.
GAS TURBINE (PG-9171E)
No/Less environmental Hazards. Control reliability.
1.1.3 CAPTIVE POWER PLANT
Captive power plant has 6 Gas Turbines each is having a capacity of 126 MW.
All Gas Turbines are Frame -9E machines of GE France make and Mark-VI controlled. Frame-PG 9171 E PG- Packaged Generator 9- Frame 9 17- 17 * 10,000 HP 1- Single shaft E- Machine series
ISO conditions = 1.01325 Bar atm pressure( MSL) = 15 oC
= 60 % RH
ISO rating of Frame - 9171 Gas Turbine = 126 MW
1.1.4 COMBINED CYCLE OR CO-GEN MODE
Graph 1.1 ( c ) and will explain the suitability of Gas Turbine based combined cycle power plants over conventional steam turbine based power plant , nuclear power plants etc.
In modern days Gas Turbine Based power plants are becoming more and more popular mainly because of it's higher efficiency, Reliability, Quick response.
In the modern Power Plants Gas Turbine Exhaust is connected to Heat Recovery Steam Generator where the steam is generated from hot gases and Steam is utilized for running the Steam Turbine such system is known as combined cycle power plants and where steam is utilized for various processes such system is called as Co-generation system
Normally combined cycle power plant efficiency is around 48-50 % and co-generation system efficiency is around 80 % depending up on application.
Reliance Petroleum Limited at Jamnagar has combination of these both combined cycle and co-generation system.
Reliance Petroleum Limited has 756 MW captive power plant , which we can call a Combined Cycle Power Plant consists of
6 x 126 MW Frame-9E (GE France) supplied by GE Energy Products France
GAS TURBINE (PG-9171E)
Gas Turbine operates on Brayton Cycle and Steam Turbine works on Rankine cycle , In combined cycle both these cycles are combined hence such power plants are called combined cycle power plant.
Typical combined cycle diagram is explained in drawing. (figure 1.C)
1.1.5 GAS TURBINE FUNCTIONAL DESCRIPTION:
When the turbine starting system is actuated and the clutch is engaged, ambient air is drawn through the inlet plenum assembly, filtered, then compressed in the 17th stage,
axial flow compressor. For pulsation protection during start-up, the 11th stage
extraction
valves are open and the variable inlet guide vanes are in the closed position.
When the speed relay corresponding to 95 per cent speed actuates, the 11th
stage extraction bleed valves close automatically and the variable inlet guide vane actuator energizes to open the inlet guide vanes (I.G.V.) to the normal turbine operating position.
Compressed air from the compressor flows into the annular space surrounding the
four-teen combustion chambers, from which it flows into the spaces between the outer
combos-tion casings and the combuscombos-tion liners. The fuel nozzles introduce the fuel into each of the fourteen combustion chambers where it mixes with the combustion air and is ignited by both (or one, which is sufficient) of the two spark plugs.
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GAS TURBINE (PG-9171E)
At the instant one or both of the two spark plugs equipped combustion chambers is ignited, the remaining combustion chambers are also ignited by crossfire tubes that connect the reaction zones of the combustion chambers. After the turbine rotor approximates operating speed, combustion chamber pressure causes the spark plugs to retract to remove their electrodes from the hot flame zone. The hot gases from the combustion chambers expand into the fourteen separate transition pieces attached to the aft end of the combustion chamber liners and flow towards the three stage turbine section of the machine. Each stage consists of a row of fixed nozzles followed by a row of rotatable turbine buckets. In each nozzle row, the kinetic energy of the jet is increased, with an associated pressure drop, and in each following row of moving buckets, a portion of the kinetic energy of the jet is absorbed as useful work on the turbine rotor. After passing through the 3rd stage buckets, the exhaust gases are directed into the exhaust hood and diffuser which contains a series of turning vanes to turn the gases from the axial direction to a radial direction, thereby minimizing exhaust hood losses. Then, the gases pass into the exhaust plenum ...
The resultant shaft rotation is used to turn the generator rotor, and drive certain accessories.
1.2 GAS TURBINE CONSTRUCTION FEATURES
Gas Turbine mainly divided in Three sections…
Compressor
Combustion system
Turbine
1.2.1 COMPRESSOR Introduction :
The axial flow compressor is consisting compressor rotor and the enclosing casing. The compressor casing consisting of Inlet Guide Vanes , 17 stages of rotor and stator balding , and 2 exit guide vanes.
In the compressor air is compressed in stages by series of alternate rotor and stator airfoil-shaped blades. The rotor blade supply the force needed to compress the air in each stage and stator blade guides the air so that it enters the following rotor stage at proper angle. The compressed air exits through the compressor discharge casing to the combustion chambers.
Air is extracted from the compressor for turbine cooling, bearing sealing and during start-up pulsation control.
Minimum clearance between the rotor and stator blade gives the best performance, all parts are to be assembled very carefully.
Compressor Rotor
The compressor rotor is an assembly of 15 individual wheels , 2 stub shaft , through bolts, and compressor rotor blades. The first stage blades are mounted on the wheel portion of the forward stub-shaft.
GAS TURBINE (PG-9171E)
Each wheel and wheel portion of each stub-shaft has slots broached around its periphery : rotor blades are inserted into these slots and they are in axial position by stacking at each end of slot.
The seventeenth stage wheel has long extension as a flow passage for turbine cooling air that is extracted from compressor between the sixteenth and seventeenth-stage wheels. The air is used to cool:
1, 1st and 2nd stage buckets
2, 2nd stage Aft & 3rd stage forward rotor wheel space
3,Also maintains turbine rotor at Compressor Discharge Temperature(355oC)
4, 1st stage wheel space is cooled by air passes through high pressure pacing seal at aft end of compressor rotor
The forward stub shaft is machined to provide the active and inactive thrust faces and journal for No.1 bearing , as well as the sealing surfaces for the No.1 bearing oil seals and the compressor low air pressure seal.
Stages 5,6.7 & 8 compressor rotor blades are coated with specialized material to avoid corrosion due to moisture formation at this region
Extraction air for rotor & wheel space cooling
Aft stub shaft 17th stage
compressor rotor blade
17th stage Compressor rotor
Specially coated rotor blades
GAS TURBINE (PG-9171E)
Compressor Stator:
The stator of compressor is mainly consists of Three major sections
Inlet Casing
Forward Compressor Casing
Aft compressor Casing
Compressor discharge casing.
These sections, in conjunction with the Turbine shell and exhaust frame form the primary structure of Gas Turbine. They support the rotor at bearing points and constitute the outer wall of gas path. The casing bore is maintained to close tolerances with respect to rotor blade tips for maximum efficiency
Inlet casing (8 struts)
Compressor discharge casing 11 to 17 th compressor stages, exit guide vanes & support for no:02 bearing
Aft compressor casing (5-10 compressor stages) Forward Compressor casing (4 compressor stages)
Location of Combustion Chambers (14 nos)
Fwd leg support
Turbine Aft Leg Support water cooled
Compressor stator wheel tie bolts
GAS TURBINE (PG-9171E)
are held in place with locking keys. In stages 5 through 17 , the stator blades and exit guide vanes are inserted directly into circumferential grooves in casing. Locking are used as with the blade ring design.
1.2.2 COMBUSTION SYSTEM Introduction :
The combustion system is the reverse flow type which includes 14 combustion chambers having the components like:
Combustion Liners
Flow sleeves
Transition pieces
Cross fire Tubes
Flame detectors
Fuel Nozzles
Spark plugs
Hot gases generated from burning the fuel in combustion chambers , are used to drive the Turbine. The photograph shows out side look of combustion system.
Compressor stator blades Compressor stator
Speed pick ups probe for turbine speed measurement (total 6 nos) 3- used for normal speed measure 3- used for overspeed measurement
Bearing no:01 Eliptical Journal Loaded thrust bearing Unloaded thrust bearing
GAS TURBINE (PG-9171E)
In reverse flow system high pressure air from compressor discharge is directed around the transition pieces and into the annular spaces that surrounds each of 14 combustion liners.
Compressor discharge air which surrounds the liner , flows radially inward through small holes in liner wall and impinges against rings that brazed to liner wall. This air then flows right toward the liner discharge end and forms a film of air that shields the liner wall from the hot combustion gases.
Fuel is supplied to each combustion chamber through a nozzle that functions to disperse and mix the fuel with proper amount of combustion air.
Combustion chambers
Discharge air from axial flow compressor enters the combustion chambers from the cavity at the center of the unit. The air flows upstream along the outside of combustion liner towards liner cap. This air enters the combustion chamber reaction zone through the fuel nozzle swirl tip and through metering holes in both the cap and liner.
The hot combustion gases from the reaction zone passes through a thermal soaking zone and then in to dilution zone where additional air is mixed with the combustion gases. Metering holes in dilution zone allow the correct amount of air to
enter and cool the gases to the desired temperature. Along the length of the combustion liner and in the liner cap are openings whose function is to provide a film
of air for cooling the walls of the liner and cap. The transition pieces direct the hot gases from the liners to the Turbine noz
Location of spark plugs Location of flame detectors Location of flame detectors
GAS TURBINE (PG-9171E)
Spark plugs
Combustion is initiated by means of the discharge from two high voltage , retractable electrode spark-plugs installed in adjacent combustion chambers. These spring -injected and pressure retracted plugs receive their energy from ignition transformers. At the time of firing , a spark at one or both of these plugs ignites the combustion gases
in the chamber , the gases the remaining chambers are ignited by cross-fire through the tubes that interconnect the reaction zones of remaining chambers. As rotor speed increases, chambers pressure causes the spark plugs to retract and the electrodes are removed from the combustion zones.(spark plug locations at CC: 13 & 14)
Ultraviolet flame detectors
During the starting sequence , it is essential that an indication of the absence of flame to be transmitted to control system. For this reason , a flame monitoring
Transition pieces attached to first stage nozzle Transition Piece Combustion Liner
GAS TURBINE (PG-9171E)
system is used consisting of four sensors which are installed on tow adjustment combustion chambers and an electronic amplifier which is mounted in the Turbine control panel.
The ultraviolet flame sensor consists of flame sensor , containing a gas filled detector. The Gas within this flame sensor detector is sensitive to the presence of ultraviolet radiation which is emitted by a hydrocarbon flame. A DC voltage , supplied by amplifier, is impressed across the detector terminals. If flame is present , the ionization of gas in the detector allows conduction in the circuit which activates the electronics to give an output defining flame. Conversely , the absence of flame will generate an opposite output defining " No flame ".
The four flame detectors are located in the combustion chamber No 4 , 5 , 10 , 11 out of total 14 combustion chambers.
Fuel nozzles
Each combustion chamber is equipped with a fuel nozzle that emits a metered amount of fuel into the combustion liner. Gases fuel is admitted directly into each chamber through metering holes located at the outer edge of the swirl plate. When liquid fuel is used , it is atomized in the nozzle swirl chamber by means of high pressure air. The atomized fuel/air mixture is then sprayed into the combustion zone. Action of the swirl tip imparts a swirl to the combustion air with the result of more complete combustion and essentially smoke free operation of the unit.
Crossfire tubes
The 14 combustion chambers are interconnected by means of cross fire tubes , these crossfire tubes propagate the flame to other combustion chambers.
1.2.3 TURBINE
The three stage turbine section is the area in which energy in the form of high energy , pressurized gas produced by compressor and combustion section is converted in to mechanical energy.
Rotor
The turbine rotor assembly consists of two wheel shafts: the first, second, and third-stage turbine wheels with buckets; and two turbine spacers. Concentricity
GAS TURBINE (PG-9171E)
control is achieved with mating rabbets on the turbine wheels, wheel shafts, and spacers. The wheels are held together with through bolts, Selective positioning of rotor members is performed to minimize balance corrections.
The forward wheel shaft extends from the first-stage turbine wheel to the aft flange of the compressor rotor assembly. The journal for the no 02 bearing is a part of
the wheel shaft.
The aft wheel shaft connects from the third-stage turbine wheel to the load coupling. It includes no 03-bearing journal.
Spacers between the first and second, and between the second and third-stage turbine wheels determine the axial position of the individual wheels. These spacers carry the diaphragm sealing bands. The spacer forward face includes radial slots for cooling air passages. The 1-2 spacer also has radial slots for cooling air passages on the aft face.
Turbine rotor must be cooled to maintain reasonable operating temperatures and, therefore, assure a longer turbine service life.
Cooling is accomplished by means of a positive flow of cool air radially outward through a space between the turbine wheel with buckets and the stator, into the main gas stream. This area is called the wheel space.
The turbine rotor is cooled by means of a positive flow of relatively cool( relative to hot gas path air) air extracted from the compressor. Air extracted through the rotor, ahead of the compressor 17th stage, is used for cooling the 1st and 2nd
stage buckets and the 2nd stage aft and 3rd stage forward rotor wheel spaces. This air
also maintains the turbine wheels, turbine spacers, and wheel shaft at approximately compressor discharge temperature to assure low steady state thermal gradients thus ensuring long wheel life.
The first stage forward wheel space is cooled by air that passes through the high pressure packing seal at the aft end compressor rotor. The 1st stage aft and 2nd
stage forward wheel spaces are cooled by compressor discharge air that passes through the stage-1 shrouds and then radially inward through the stage-2 nozzle vanes. The 3rd aft wheel space cooled by cooling air that exits from the exhaust
GAS TURBINE (PG-9171E)
Buckets
The turbine buckets increase in size from the first stage to the third stage. Because of the pressure reduction resulting from energy conversion in each stage , an increased annulus area is required to accommodate the gas flow . The first stage buckets are the first rotating surfaces encountered by extremely hot gases leaving the first stage nozzle. Each first stage bucket contains a series of longitudinal air passages for bucket cooling. The holes are shaped and sized to obtain optimum cooling of airfoil with the minimum of compressor extraction.
Like the first-stage buckets, the second-stage buckets are cooled by span wise air passages the length for the air-foil. Since the lower temperatures surrounding the bucket shanks do not require shank cooling, the second-stage cooling holes are fed by a plenum cast into the bucket shank. Span wise holes provide cooling air to the airfoil at a higher pressure than a design with shank holes. This increases the cooling effectiveness in the airfoil so airfoil cooling is accomplished with minimum penalty to the thermodynamic cycle
The third stage buckets are not internally air cooled; the tips of these buckets, like the second-stage buckets, are enclosed by a shroud which is a part of the tip seal. The shrouds interlock from bucket to bucket to provide vibration damping.
Turbine Rotor Turbine first stage rotating buckets
Turbine second stage rotating blades
Turbine third stage rotating blades
GAS TURBINE (PG-9171E)
STATOR Turbine shell :
The turbine shell controls the axial and radial positions of the shrouds and nozzles. It deter-mines turbine clearances and the relative positions of the nozzles to the turbine buckets.This positioning is critical to gas turbine performance.
Hot gases contained by the turbine shell are a source of heat flow into the shell. To control the shell diameter, it is important that the shell design reduces the heat flow into the shelland limits its temperature. Heat flow limitations incorporate insulation, cooling, and multi-layered structures. The external surface of the shell incorporates cooling air passages.Flow through these passages is generated by an off base cooling fan.
Structurally, the shell forward flange is bolted to flanges at the aft end of the compressor discharge casing and combustion wrapper. The shell aft flange is bolted to the forward flange of the exhaust frame. Trunnions cast onto the sides of the shell are used with similar trunnions on the forward compressor casing to lift the gas turbine when it is separated fromits base.
Turbine 1st stage rotating
buckets with cooling holes
Bucket trailing edge Bucket leading edge
Turbine 2nd stg nozzle
Turbine 3rd stage
GAS TURBINE (PG-9171E)
Turbine nozzles :
In the turbine section, there are three stages of stationary nozzles which direct the high velocity flow of the expanded hot combustion gas against the turbine buckets, causing the rotor to rotate. Because of the high pressure drop across these nozzles, there are seals at both the inside diameters and the outside diameters to prevent loss of system energy by leakage. Since these nozzles operate in the hot combustion gas flow, they are subjected to thermal stresses in addition to gas pressure loadings.
First stage nozzle :
The first stage nozzle receives the hot combustion gases from the combustion system via the transition pieces. The transition pieces are sealed to both the outer and inner sidewalls on the entrance side of the nozzle, so minimizing leakage of compressor discharge air into the nozzles. The 18 cast nozzle segments, each with two partitions (or airfoils) are contained by a horizontally split retaining ring which is center-line supported to the turbine shell on lugs at the sides and guided by pins at the top and bottom vertical center-lines. This permits radial growth of the retaining ring, resulting from changes in temperature while the ring remains centered in the shell.
The aft outer diameter of the retaining ring is loaded against the forward face of the first stage turbine shroud and acts as the air seal to prevent leakage of compressor discharge air between the nozzle and shell. On the inner sidewall, the nozzle is sealed by direct bearing of the nozzle inner load rail against the first-stage nozzle support ring bolted to the compressor discharge casing. The nozzle is prevented from moving forward by four lugs welded to the aft outside diameter of the retaining ring at 45 degrees from vertical and horizontal centerlines. These lugs fit in a groove machined in the turbine shell just forward of the first stage shroud T-hook. By moving the horizontal joint support block and the bottom centerline guide pine, the lower half of the nozzle can be rolled out with the turbine rotor in place.
Turbine first stage nozzle 18 cast nozzles (18*2)= 36
GAS TURBINE (PG-9171E)
Second stage nozzle :
Combustion gas exiting from the first stage buckets is again expanded and redirected against the second stage turbine buckets by the second stage nozzle.
The second stage nozzle is made of 16 cast segments, each with three partitions (or air-foils). The male hooks on the entrance and exit sides of the sidewall fit into female grooves on the aft side of the first stage shrouds and on the forward side of the second stage shrouds to maintain the nozzle concentric with the turbine shell and rotor. This close fitting tongue-and-groove fit between nozzle and shrouds acts as an outside diameter air seal.The nozzle segments are held in a circumferential position by radial pins from the shell into axial slots in the nozzle outer sidewall. The second stage nozzle partitions are cooled with compressor discharge air.
Third stage nozzle
:The third stage nozzle receives the hot gas as it leaves the second stage buckets, increases its velocity by pressure drop and directs this flow against the third stage buckets.
The nozzle consists of 16 cast segments, each with four partitions (or airfoils). It is held at the outer sidewall forward and aft sides in grooves in the turbine shrouds in a manner identical to that used on the second stage nozzle. The third stage nozzle is circumferentially positioned by radial pins from the shell.
The turbine shell and the exhaust frame complete the major portion of the Gas Turbine stator structure. The turbine nozzles , shrouds , No-3 bearing and turbine exhaust diffuser are internally supported from these components.
The turbine shell controls the axial and radial positions of the shrouds and nozzles. Resultantly, it controls turbine clearances and relative positions of the nozzles to the turbine buckets. This positioning is critical to the gas turbine performance.
Hot gases contained by turbine shell are the source of heat flow into the shell. To control the shell diameter , it is important to reduce the heat flow into shell by design and to cool it to limit it's temperature. Heat flow limitations incorporate insulation , cooling, and multi-layered structures. The cylindrical portion of shell is cooled by fifth stage air flowing axially through the shell and out through holes in the aft vertical flange into the exhaust frame. The air is then used for further cooling of exhaust frame and third stage aft wheel space
Structurally , the shell forward flange is bolted to the bulk head at the aft end of compressor discharge casing. The shell aft flange is bolted to the exhaust frame cast onto sides of shell are used to aid in lifting the gas turbine when it is separated from its base , should this ever by necessary.
Diaphragms :
Attached to the inside diameters of both the second and third stage nozzle segments are the nozzle diaphragms These diaphragms prevent air leakage past the inner sidewall of the nozzles and the turbine rotor. The high/low, labyrinth-type seal teeth are machined into the inside diameter of the diaphragm. They mate with opposing sealing lands on the turbine rotor. Minimal radial clearance between
GAS TURBINE (PG-9171E)
stationary parts (diaphragm and nozzles) and the moving rotor are essential for maintaining low interstage leakage ; this results in higher turbine efficiency.
Shrouds :
Unlike the compressor balding, the turbine bucket tips do not run directly against an integral machined surface of the casing but against annular curved segments called turbine
shrouds .
The primary function of the shrouds is to provide a cylindrical surface for minimizing tip clearance leakage.
The secondary function is to provide a high thermal resistance between the hot gases and the comparatively cool shell. By accomplishing this function, the shell cooling load is drastically reduced, the shell diameter is controlled, the shell roundness is maintained, and important turbine clearances are assured. The shroud segments are maintained in the circumferential position by radial pins from the shell. Joints between shroud segments are sealed by interconnecting tongues and grooves.
Stage2 nozzle 16*3=48 3rd stg nozzle 16*4=64 2nd stage shroud 3rd stage diaphragm 2nd stage Diaphragm 1st stage bucket
1st stg aft outer wheelspace
1st stage
GAS TURBINE (PG-9171E)
1.2.4 EXHAUST FRAME AND DIFFUSER
The exhaust frame assembly (figure here after) consists of the exhaust frame and the exhaust diffuser. The exhaust frame is bolted to the aft flange of the turbine shell.
Structurally, the frame consists of an outer cylinder and inner cylinder interconnected by ten radial struts. On the inner gas path surfaces of the two cylinders are attached the inner and outer diffusers. The no.3 bearing is supported from the inner cylinder.
The exhaust diffuser, located at the extreme aft end of the gas turbine, bolts to, and is supported by, the exhaust frame. The exhaust frame is a fabricated assembly consisting of an inner cylinder and an outer divergent cylinder that flairs at the exit end at a right angle to the turbine centerline. At the exit end of the diffuser between the two cylinders are five turning vanes mounted at the bend. Gases exhausted from the third turbine stage enter the diffuser where velocity is reduced by diffusion and pressure is recovered. At the exit of the diffuser, turning vanes direct the gases into the exhaust plenum. Exhaust frame radial struts cross the exhaust gas stream. These struts position the inner cylinder and n0.3 bearing in relation to the outer casing of the gas turbine. The struts must be maintained at a uniform temperature in order to control the center position of the rotor in relation to the stator. This temperature stabilization is accomplished by protecting the struts from exhaust gases with a metal fairing fabricated into the diffuser and then forcing cooling air into this space around the struts.
Turbine shell cooling air enters the space between the exhaust frame and the diffuser and flows in two directions. The air flows in one direction into the turbine shell cooling annulus and also down through the space between the struts and the airfoil fairings surrounding the struts and subsequently into the load shaft tunnel and turbine third-stage aft wheelspace.
GAS TURBINE (PG-9171E)
Outer cylinder Inner cylinder
Exhaust Frame Air Foil strut Exhaust Frame
GAS TURBINE (PG-9171E)
DESIGN INPUT DATAA. COMBUSTION TURBINE GENERATOR INPUT DATA
Cycle description Combined Cycle with Cogeneration
I. Combustion Turbine
a. Nominal Output Rating, MW 116 b. Type of Combustion Turbine: PG9171E
Compression Ratio 12.65 Gas/12.61 Liquid
1) heavy frame / aeroderivative Heavy frame c. Type of inlet air filter Self-cleaning, pulse type e. Material of Individual Inlet Air Filter Elements Synthetic
f. CTG location (indoors/outdoors) Outdoors h. Diluent Injection (for NOx control) Water
i. Diluent filter rating (microns)
j. Injection for power augmentation N/A k. Inlet cooling type N/A
Effectiveness
N/Al. Stack (diameter / height) 30 M Height m. Fuel Gas Conditioning Equipment
n. Liquid fuel filter rating (microns) To be specified by Seller o. Number of water wash skid(s) 2
p. Type of water wash skid (fixed or portable) Fixed q. Starting system type Motor (1.1 MW) s. Required purge flow (percentage of ISO base
load flow) 8 percent per NFPA 85 t. Lubrication oil system filter rating (microns) 10
u. Lift oil system filter rating (microns) v. Hydraulic oil system filter rating (microns)
II. Generator
a. Type of gen. cooling
air) TEWAC
b. Generator Design Standard (ANSI / IEC) IEC
c. Type of Excitation System (static / brush less) Brush less, feed from generator terminals
GAS TURBINE (PG-9171E)
(at rated voltage) 47.5 Hz to 52.5 Hz f. Generator power factor range 0.8 Lag to 0.95 Lead g. Generator rated terminal voltage 14.5 KV h. Generator surge capacitor rating (if applicable)
i. Generator lightning arrestor MCOV
j. Generator minimum short circuit ratio 0.56 k. Generator Phase Sequence
l. Neutral bus grounding resistor assembly rating Transformer with resistor m. Generator line side connection
1) Bus duct (isophase/ non-segregated phase) Iso-phase 2) Mounting location (top, side, bottom)
3) Current transformer accuracy (class) n. Generator neutral side
1) Mounting location (top, side, bottom) 2) Current transformer accuracy (class)
o. Generator excitation system response time Exciter response to be of the High Initial Type, at rated full load
condition Less than 0.1 seconds p. Governor regulation adjustable range 4% - 10% q. System fault contribution
(for power system stabilizer)
r. Generator excitation minimum response ratio 2.0 static
s. Generator shaft voltage monitoring
b. Bently-Nevada Vibration System (3300/3500) 3500 c. Gauges and indicators – system of units
(English, SI, or both) SI d. Gas Fuel Meter
1) Type (orifice, turbine, ultrasonic) 2) Accuracy
3) Calibration
e. Liquid Fuel Flow Meter
1) Type Coriolis meter 2) Accuracy
GAS TURBINE (PG-9171E)
3) Calibration
IV. Auxiliaries
a. Common lube oil/control oil system acceptable
(yes/no) Common lube oil system
V. Miscellaneous
c. Thermal insulation design criteria
1) Maximum surface temperature 60°C 2) Ambient Temperature
3) Wind Velocity
VII. Noise Guarantee
a. Guaranteed Noise Level (sound pressure level), dBA referenced to 20μPa, measured at a
distance of 1 m at a height of 2 m 85dBA
1.3 EQUIPMENT DATA GAS TURBINE DESIGN DATA
CUSTOMER : Reliance Petroleum Limited
SITE : Jamnagar Export Refinery Project
UNIT(S) NUMBER(S) :
TYPE : PG 9171 E
GAS TURBINE APPLICATION : GENERATOR DRIVE
CYCLE : SIMPLE
TYPE OF OPERATION : BASE
ALTITUDE : Sea level
COMPRESSOR : STAGES : 17 SPEED : 3000 R.P.M.
TURBINE : STAGES : 3 SPEED : 3000 R.P.M.
DESCRIPTIVE GUIDE
GAS TURBINE EQUIPMENT DATA SUMMARY COMPRESSOR SECTION
Number of compressor stages : Seventeen (17)
Compressor type : Axial Flow, Heavy duty Casing split : Horizontal, Flange Inlet guide vanes type : Modulated
TURBINE SECTION
Number of turbine stages : Three(3) single shaft Casing splits : Horizontal
Nozzles : Fixed Area
COMBUSTION SECTION
Type : Fourteen (14) multiple combustors, reverse flow
GAS TURBINE (PG-9171E)
Fuel nozzles : One ( I ) per combustion chamber
Spark plugs : Two (2), electrode type. Spring-injected self-retracting
Flame detectors : Four (4) Ultra Violet Type BEARING ASSEMBLIES
Quantity : Three
Lubrication : Pressure lubricated No I bearing assembly (located in
inlet casing assembly) : Active and inactive thrust and journal, all contained
in one assembly
Journal : Elliptical
Active thrust : Tilting pad, self-equalizing
Inactive thrust : Tapered land
No 2 bearing assembly (located in the
compressor discharge casing) : Elliptical journal
No 3 bearing assembly (located in the
exhaust frame) : Journal, Tilting pad
STARTING SYSTEM
Starting device : Electrical starting motor
Torque converter : Hydraulic with adjustor drive
FUEL SYSTEM
Operating type : Natural gas + distillate fuel
Fuel control signal : SPEEDTRONIC MARK-VI control system
Fuel pump : Accessory gear-driven. Continuous output screw type Pump
Flow divider (starting motor) : Circular, free wheeling, 14 elements
Fuel oil stop valve : Electro-hydraulic servo-control
Fuel oil filter(s) (H.P.) : Two (2), full flow, HP strainer
GAS TURBINE (PG-9171E)
LUBRICATION SYSTEMLubricant : Petroleum base Total capacity : 12,491 liters (approx.)
Main lube pump : Shaft-driven, integral with accessory gear
Auxiliary lube pump : A.C. motor-driven, vertical, submerged, centrifugal type
Emergency lube pump : D.C. motor-driven, vertical, submerged, centrifugal type
Heat exchanger(s)
Type :Oil heat to fresh water Quantity : Two (2) in parallel
Filter(s)
Type : Full flow with transfer valve Quantity : Two (2)
Cartridge type : Five micron filtration pleated paper
HYDRAULIC SUPPLY SYSTEM
Main hydraulic supply pump : Accessory gear-driven, variable positive displacement, axial piston
Auxiliary hydraulic supply pump : Driven by electric motor 88 HQ.
COOLING WATER SYSTEM (in closed loop)
Pumps : Two (2) water pumps located on the water skid
outside of the G.T. building
ATOMIZING AIR SYSTEM
Main compressor : Accessory geardriven centrifugal
Starting (booster) compressor : Axial flow, positive displacement, belt driven
by an
electric motor
Air precooler : Air-to-water heat exchanger
PROTECTION : over temperature, vibration, flame detection Nox control system : DM water injection method
GAS TURBINE (PG-9171E)
Expected Operating Parameters: (on Natural Gas fuel)TNH FSR TNR GCV FLOW GCV outlet pr % % % mm NM3/hr barag Firing 12 19.8 ---- 8.8 1649 ---Warm up 16 9.5 ---- 4.2 809.16 ---FSNL 100 15.7 100 7 9399.44 9.7841 Base Load 100 63.2 103.66 28.1 36400.5 17.3977
Expected Operating Parameters: (on Liquid fuel)
TNH FSR TNR Flow divider speed FLOW Fuel Injection pr % % % Hz L/min Barg
Firing 15 19.8 ---- 33 17.2 ---No Load 100 14.5 100 240 126.2 17.2 Base Load 100 69.3 104 2277 603.3 37
1.4 GAS TURBINE CONTROLS BASIC CONTROL PHILOSOPHY
The Gas Turbine has a number of control and protection system designed for reliable and safe operation of Gas Turbine.
Control of Turbine is done mainly by start-up , speed , acceleration , synchronization and temperature control.
The figure explains the means of fuel control in relation to fuel command signal sensors monitor the turbine speed , temperature and compressor discharge pressure to
No: 02 bearing Combustion chamber Total# 14 nos. Crossfire tube location No:03 bearing
GAS TURBINE (PG-9171E)
determine the operating condition of Gas turbine. When it is necessary for turbine control to alter the turbine operating conditions because of changes in load or ambient conditions , it is performed by modulating the fuel flow
to turbine. e.g. if exhaust temperature starts exceeding it's permissible value for given operating conditions temperature control circuit will cause a reduction in fuel supply and limit the exhaust temperature.
Gas Turbine control system is designed to monitor the critical parameters which are : Temperature , Vibrations , speed , Flame , Fuel flow etc.
SPEEDTRONIC DESIGN
The SPEEDTRONIC system is microcomputer based system which provides analog as well as digital signals require to control and protect the turbine.
Operating conditions are sensed and utilized as feedback signal to SPEEDTRONIC control system. There are three major control loops --Start-up , Speed and Temperature which may be in control during turbine operation. The output of this control loops is connected to minimum select circuit.
The minimum value select circuit connects the speed , temperature and start-up control output signals to the FSR controller. The lowest voltage output of control loops is allowed to pass the gate to fuel control system as controlling FSR ( Fuel Stroke Reference ) voltage. FSR is the command signal for fuel. Switching between the control modes of speed , temperature and start-up control takes place without any discontinuity.
FSR CONTROL
START-UP CONTROL
BASICS :
14 HR - Zero Speed
14 HM - Minimum firing speed
14 HC - Self sustaining speed
14 HA - Accelerating Speed
14 HS - Full Speed ( 95 % )
SPEED CONTROL
The speed control system is designed to control the speed and load of turbine operating in response to actual speed signal and speed reference. While on speed control the control mode will be " Droop Speed "
GAS TURBINE (PG-9171E)
DROOP OPERATIONThe speed control software will change FSR in proportion to the difference
between the actual turbine speed and speed reference ( TNR ). Once the generator
breakers are closed on power grid , speed is held relatively constant at synchronous speed , the fuel flow in excess of that necessary to maintain full speed no load , will result not in increased speed but , in increased power produced by generator. The speed control loop is acting as a load control loop and the speed reference is a convenient control of desired load on turbine generator unit.
The speed control is proportional and it changes FSR in proportion to the difference between the actual turbine speed and speed reference. Thus any change in frequency will also cause proportional change in load. This proportionality is adjustable to desired regulation which is called DROOP.
When entire grid system will overload the grid frequency will reduce and FSR will increase in proportion to droop
settings. If all units have the same droop setting all units will share a load increase equally. Load sharing is the main advantage of this method of droop control.
If 4 % droop is selected , only 1 % change in speed will produce a change in fuel flow equivalent to 25 % of rated load.
Normally 4 % droop is selected and set point is calibrated such that 104 % set point will generate a speed reference which will produce FSR resulting in Base Load at design ambient temperature.
See Droop v/s FSR graph
Constant Settable Droop :
This method of load control is applied where FSR is not predictable as a function of the gas turbine power output.
This means , When the gas turbine fuel heating value is varying due to changes in fuel composition or fuel is switched between different combustion system this type of load control method is normally adopted.
Constant settable droop is an inner speed control loop and outer megawatt control loop. The inner speed control loop is a proportional plus integral control whose mission is to make turbine speed TNH match the speed reference command TNRL. The outer megawatt loop formulates the droop governor response by creating a speed bias as function of unit power output. When turbine speed is held fixed by electrical grid , the turbine fuel consumption ( FSR ) and megawatt output is modified ( Constantly set ) such that TNRL reference speed command is made equal the turbine speed TNH.
GAS TURBINE (PG-9171E)
TEMPERATURE CONTROLGas Turbine Firing temperature is determined by the measured parameters of exhaust temperature and CPD or exhaust temperature and fuel consumption ( FSR ). The temperature control reference program calculates the exhaust temperature control set point based on CPD and other control constants. The algorithm also calculates another set point based on FSR and its set of control constants.
CPD bais :
When ever CPD increases beyond pre-determined value , the compressor discharge temperature will also increases hence firing temperature will also increase , Now due to metallurgical limitations , firing temperature will not be permitted to increase beyond certain limits hence to control firing temperature CPD bias will reduce the exhaust temperature control set point and thereby reducing firing temperature.
FSR bias:
Fuel flow to combustion chamber will not be allowed to increase more than predetermined value , hence depending up the quality of fuel ( HSD , Kerosene , Naphtha , Gas ) and calorific value fuel , Fuel flow to the combustion chamber is limited to certain value ( FSR ) , In case fuel flow ( FSR ) increases beyond this limit , the firing temperature is going rise,hence to limit the firing temperature , temperature control set point is reduced to keep acceptable firing temperature.
Normally this will come in line when CPD signal fails or drastic change in fuel quality.
The CPD bias TTK()_C corner and CPD bias TTK()_S slop with the CPD data determines the CPD bias exhaust temperature set point
The FSR bias TTK()_K corner and FSR bias TTK()_M slop with the FSR data determines the FSR bias exhaust temperature set point.
The temperature-control-bias program also selects the TTK()_I Isothermal set point.
The program selects the minimum of the three set points CPD bias , FSR bias and
Isothermal set point for the final exhaust temperature control reference.
During the normal operation of Gas Turbine with Gas or light fuel , this selection results in CPD bias control with an Isothermal limit.
The CPD bias set point is compared with FSR bias set point and alarm occurs when CPD bias set point is higher than the FSR bias set point.
During the normal operation of Gas Turbine with heavy fuel , this selection results in FSR bias control with an Isothermal limit.
The FSR bias set point is compared with CPD bias set point and alarm occurs when FSR bias set point is higher than the CPD bias set point.
GAS TURBINE (PG-9171E)
Temperature reference is reduced if compressor discharge pressure signal is less than a calculated operating speed minimum. This failure is alarmed " CPD signal low ". This failure reduces the FSR bias , to permit the operation at rated firing temperature. Temperature control reference is increased or decreased manually , but this will not affect over temperature trip and alarm set point.
The temperature control fuel stroke reference algorithm compares the exhaust temperature control set point with the measured gas turbine exhaust temperature as obtained from T.C. mounted in the exhaust plenum. These signals are accessed by RST as well as by C.
TTXC is the average temperature
TTXM is the median temperature.
temp cont temp control1
INLET GUIDE VANE AND EXHAUST TEMPERATURE CONTROL.
During the normal start-up , the inlet guide vanes are held in the full closed position until the proper temperature corrected speed is reached , at which time IGV begin to open. During the Full Speed No Load or Less than 20 % load operation the IGV will remain minimum Full open position. The compressor bleed valves , which must operate in conjunction with the guide vanes to maintain compressor surge margin , will close when generator breaker is closed.
When the IGV temperature control is not activated and IGV is in a simple cycle mode , the guide vanes are held at the minimum full speed angle until the simple cycle IGV exhaust temperature set point is reached. This temperature control set point is programmed in the software at approximately ( 371 deg C )
Wherever GT is installed at the exhaust of Gas Turbine which require exhaust temperature control by inlet guide vanes , the guide vanes are held at the minimum full speed angle until combined cycle IGV exhaust temperature set point is reached. The IGV temperature control set point is programmed at a value slightly lower than the BASE temperature control set point , with the CPD bias. The dark line traces a typical exhaust temperature pattern as the gas turbine output changes.
Point "A" is the operating point at the end of the start-up with IGV positioned at the minimum full speed angle. As output increases , the IGV is held at this minimum angle until IGV temperature control set point is reached Point "B". Now between point "B" and point "C" IGV is opened to maintain setpoint temperature as output is further increased. At point "C" IGV is at it's full open position and upon further increase in output the turbine will reach to its Base temperature set point limit "D".
The trace of exhaust temperature for IGV in simple cycle mode , from point A* to B' to C' to D for full speed no load to full load.
GAS TURBINE (PG-9171E)
1.5 GAS TURBINE OPERATING SYSTEMS:Lube oil Schematic:
1.5.1 Lube Oil system: Schematic:
The lubrication system produces cooled, filtered oil for the bearing of the GT and the Generator. The lubricating provisions for the turbine, generator, torque converter and accessory gear box are incorporated in a common lubrication system which includes a main lubrication oil pump, full size auxiliary lube oil pump driven by AC motor, an emergency lube oil pump driven by a DC motor and oil tank with an oil-to-water heat exchanger, filters, a bearing header pressure regulator and a pressure relief valve
The lube oil is supplied by the main lubrication oil pump (shaft driven from accessory gear) during normal stage operation of the unit or by the auxiliary AC motor driven pump during startup, turning, slowing-down and cooling periods, or by the DC motor driven pump which backs up the AC pump in some cases. These pumps are located
GAS TURBINE (PG-9171E)
pressure gauges are supplied by control, indication and protection of the lube oil system.
LUBRICATING OIL PUMPS:
Lubrication to the bearing header is supplied by three lube pumps :
1. The main lube supply pump is a positive displacement type pump mounted in and driven by the accessory gear
2. The auxiliary lube supply pump is a submerged centrifugal pump driven by an A.C motor.
3. The emergency lube supply pump is a submerged centrifugal pump driven by a D.C motor
Main lube pump:
The main lube pump is built into the inboard wall of the lower half casing of the accessory
gear. A splined quill shaft drives it from the lower drive gear. The output pressure to the lubrication system is limited by a back-pressure valve to maintain system pressure.
Auxiliary Lube oil pump:
The auxiliary lube pump is a submerged centrifugal type pump driven by an A.C. motor.
It provides lubricant pressure during start-up and shut-down of the gas turbine when the
main pump cannot supply sufficient pressure for safe operation. Operation of this pump
is as follows :
A low lube oil pressure alarm transmitter (96 controls the auxiliary lube pump
QA-1). This low pressure level alarm causes the auxiliary pump to run under low lube oil pressure conditions as is the case during start-up or shut down of the gas turbine when the main pump, driven by the accessory drive device, does not supply sufficient pressure. At turbine start-up, the A.C. pump starts automatically when the master control switch on the turbine control panel is turned to the START position.
The auxiliary pump continues to operate until the turbine reaches approximately 95 per
cent of operational speed.
At this point, the auxiliary (cool down) lube pump shuts down and system pressure is supplied by the shaftdriven, main lube pump. During the turbine starting sequence, the pump starts when the start signal is given. The control circuit is through the pressure level of pressure transmitter 96 QA-I. The pump will run until the turbine operating speed is reached (operating speed relay 14 HS picks up), even though the lube oil header is at rated pressure and the discharge pressure level (96 QA-1) is above alarm level setting.
When the turbine is on the shut-down sequence, this pressure transmitter will signal for
the auxiliary pump to start running when the lube oil header pressure falls to the point at which pressure level alarm setting is reached.
GAS TURBINE (PG-9171E)
Emergency Lube Oil Pump:
The emergency lube pump is a D.C., motor-driven pump, of the submerged centrifugal
type. This pump supplies lube oil to the main bearing header during an emergency
shut-down in the event the auxiliary pump has been forced out of service because of loss of A.C. power, or for other reasons. It operates as follows :
This pump is started automatically by the action of pressure transmitter 96 QA-2 whenever the lube pressure in the main bearing header falls below the pressure switch setting. If the auxiliary lube oil pump should resume operation, the emergency pump will be stopped by a pressure transmitter (96 QA-2) when the header pressure exceeds the
alarm setting in speedtronic.
If the auxiliary pump fail during the shut-down sequence, because of an A.C.
power failure or any other cause, the emergency lube pump will be started automatically
by the action of low lube oil pressure transmitter 96 QA-2 and continue to run until the
turbine shaft comes to rest.
Pressure regulation:
Two regulating valves are used to control lubrication system pressure. A backpressure Relief valve, VR-1, limits the positive displacement main pump discharge header
pres-sure and relieves excess fluid to the lube reservoir. The lube prespres-sure in the bearing Header is maintained at approximately 25 psig (i.e. 1.75 bar) by the diaphragm operated
Regulating valve, VPR-2. This valve has an orifice which permits 80 per cent flow. The
Diaphragm valve is operated by sensing fluid pressure in the bearing header.
Pressure and temperature protective devices:
The condition of low lubricating fluid pressure is detected by a pressure switch and transmitters that open after a decrease of line pressure to a specified value and trips the unit. Pressure switch 63 QT-2A and transmitter 96 QH-1 which are installed in the lubricant feed piping on the generator side signal an alarm if the lubricant pressure drops to an unacceptable level. Likewise, thermocouples LT-TH-lA,-I B,
LT-TH-ZA,-2B and LT_TH3A,3B are installed in the lubricating fluid header piping and
cause an alarm to sound and the unit to trip should the temperature of the lubricant to the bearings exceed a preset limit. The settings in speedtronic for the thermocouples are such that an alarm is actuated if any one of the thermocouples detects low
GAS TURBINE (PG-9171E)
This unit has a SPEEDTRONIC control system. Before the unit is tripped by either high
temperature (LT-TH-lA,-l B, LTPTH-2A,-2B and LTpTH3A,-3B), or low pressure (96 QA-1, 63 QT-2A and 96 QH-I), the cause for the trip has to be sensed by two of the three measuring devices. This ”voting logic” is to prevent a trip due to a malfunctioning
sensor.
Provisions are made for checking lube flow to the main turbine and generator bearings
by means of oil sights and thermocouples.
Other temperature measuring and/or protective devices:
There are thermocouples that can be checked by means of the T.C. selector on the gas turbine control panel : LT-TH-IA,-l B, LTPTH-2A,-2B and LT_TH3A,3B for the L.O. turbine header, LT-BI D for bearing no 1 L.O. drain, LT-B2D for bearing no 2 L.O. drain
and LT-B3D for bearing no 3 L.O. drain. LT-G1D for the L.O. system bearing no 4 (generator), LT-G2D for the L.O. system bearing no 5 (generator). LT-BT1 D for the no.
1 thrust bearing drain.
Lube fluid heat exchanger
:The heat exchanger system is required to dissipate the heat absorbed by the lubricating
fluid and to maintain the fluid at the proper bearing header temperature. This is accomplished by circulating cooling water through the cooling tubes of the heat Exchanger as the lubricant flows over the tubes. Cooling water flow through the heat Exchanger is controlled by temperature sensitive flow regulator valve VTR 1, that maintains the correct bearing temperature.
The lube fluid heat exchanger system uses a fluid-to-water cooler of the shell and tube bundle design. There is two heat exchangers, flange mounted in the lube reservoir in
a horizontal position. A U-tube bundle extends into the center of the shell through which the cooling water is passed. The lube fluid flows in and out of the shell; passing over the cooling tubes of the tube bundle. Cooling water connections are made at the external steel bonnet that bolts to the shell-mounting flange through the tube sheet that supports the tubes of the tube bundle.
Main lube filtering system:
Filtration of all lube oil is accomplished by a 5 micron, pleated paper filter installed in the lube system just after the lube oil heat exchanger.
Two (duplex) filters are used with a transfer valve installed between the filters to direct oil flow through either filter and into the lube oil header.The duplex filters arranged side by side, are installed on the tank and connected into the pump discharge header through a manual transfer valve. Only one filter will be in service at a time, thus cleaning, inspection, and maintenance of the second one can be performed without interrupting oil flow or shutting the gas turbine down. By means of the
GAS TURBINE (PG-9171E)
manually operated, worm-driven transfer valve, one filter can be put into service as the second is taken out, without interrupting the oil flow to the main tube oil header.
Filters should be changed when the differential pressure transmitter 96 QQ-1 indicates a differential pressure of 15 psig (i.e. about 1.03 bar)
ACCESSORY GEAR BOX :
The gears are lubricated by the lube oil from the lube oil header only.
These gear box contains various gears which reduces / raises speed as per the requirement of various shaft driven drives. Prominent among them were Main oil pump ( MOP ), Main Hydraulic oil pump ( MHOP ), Main atomizing air compressor.
Speed of shaft#01 in RPM # 3000 RPM (Driving shaft)
Speed of shaft#02 in RPM # 3424.2 RPM (Pinion Shaft)
Speed of shaft#03A in RPM # 1554.2 RPM (Warren fuel oil pump)
Speed of shaft#03B in RPM # 6607.2 RPM ( Main Atomizing air
compressor)
Speed of shaft#04 in RPM # 1421.9 RPM (Main Lube oil pump)
MIST ELIMINATOR
The main function of mist eliminator is to remove the oil vapor and to maintain the negative pressure at the tank to avoid the pressurization of tank and preventing the lube oil leakage from tank.
The lube comes along with the vapor is filtered and diverted back to tank and oil vapor is thrown out to the atmosphere. Normally tank pressure is to be maintained around 50 mmwc below the atmospheric pressure.
Accessory Gear Box internal view Main fuel pump
Main Lube pump
Main Hydraulic pump Main shaft
GAS TURBINE (PG-9171E)
1.5.2 COOLING WATER SYSTEM:
CW system Schematic:
3.5.1. GENERAL
The cooling water system is a pressurized, closed system, designed to accommodate the heat dissipation requirements of the turbine, the lubrication system, the atomizing air system, the turbine support legs and the flame detectors.
The cooling water system circulates water as a cooling medium to maintain the lubricating oil at acceptable lubrication system temperature levels and to cool several turbine components.
The system normally operates at a slightly positive pressure, which results when the liquid in the system expands with the increase in temperature during operation.
During operation the coolant is supplied by the owner’s cooling system and circulates through the chosen lube oil, atomizing air heat exchangers and the turbine support legs (in parallel with the other two systems of heat exchangers). After absorbing the heat rejected by these items, the coolant flows through the owner’s water cooling system where it is cooled.
GAS TURBINE (PG-9171E)
Flow regulating valves:
The coolant circuit for the lube oil and atomizing air heat exchangers each have a tempera-ture actuated 3-way valve (VTR 1 and VTR 2-1, respectively) installed in the coolant inlet line to the heat exchangers.
These type valves, which control coolant flow to the heat exchanger, have a manually operated device which can override the thermal element. The manual override device should be used only when the valve’s thermal element is inoperative but machine operation is required. Atomizing air compressor inlet and lube oil feed header temperatures are sensed by the bulb associated with each valve which controls the flow of coolant through the heat exchanger and maintains the air and lube oil temperatures at predetermined values. The valves automatically control flow of the medium passing through them (coolant) to the heat exchanger by responding to temperature changes affecting the bulb. The bulb contains a thermal-sensitive liquid which vaporizes when heated. Pressure thus generated in the bulb is transmitted through the capillary tube to the bellows, which positions the valve disc to control the flow of coolant through the heat exchanger. The valve is closed during turbine startup, and will start to open as the sensed fluid temperature approaches the control setting.
Valve VTR 2-1 in the coolant line to the atomizing air heat exchanger has a small bypass orifice drilled into the valve body to assure that the cooler is ”flooded” at all times.
At the inlet of each cooling water circuit (lube oil heat exchanger circuit, atomizing air heat exchanger circuit and turbine support legs circuit), an orifice allows water flow rate calibration to the circuit concerned.
The flame detector mounts are cooled to extend the life of the flame detectors. The coolant jackets on the flame detector mounts provide a thermal break in heat conduction from the combustion can housing to the flame detector instrument.
Temperature, pressure measuring and/or protective devices:
Thermocouples, WT-TL-1,-2 at turbine support legs outlet and WT-TD, located at GT cooling system outlet, give a GT cooling water temperature indication.
Thermocouple, WT-OCD at outlet of GT lube oil heat exchanger, give a GT
Temperature regulating valve
GAS TURBINE (PG-9171E)
1.5.3 FUEL OIL SYSTEM:
Liquid fuel Schematic:
The liquid fuel (distillate oil) system pumps and distributes fuel as supplied from the fuel forwarding system, to the fourteen fuel nozzles of the combustion system. The fuel system filters the fuel and divides the fuel flow into 14 equal parts for distribution to the combustion chambers at the required pressure and flow rates.
Controlling the position of the fuel pump bypass valve VC3 regulates the amount of fuel input to the turbine combustion system by varying the amount of bypassed fuel.
o Fuel oil strainer.
o Fuel oil stop valve VSI . o Liquid fuel pump PFI.
o Fuel pump discharge relief valve VR4. o Fuel bypass valve VC3.
o Flow divider or fuel distributor FDI o High-pressure fuel filters FF2-1,-2. o Fuel line check valves.
GAS TURBINE (PG-9171E)
o Fuel nozzle assemblies.o False start drain valves.
Control devices also associated with the fuel system include :
the liquid fuel pressure transmitter 96 FL-2, servo valve 65 FP that controls the fuel bypass valve, fuel pump clutch solenoid 20 CF-1, and permissive limit switches 33 FL-1 and -2 and trip relay valve VH 4 in the fuel oil stop valve trip control circuits.
Functional description of the fuel oil system:
Low fuel oil strainer
Fuel oil at low pressure from the fuel forwarding system, flows through a low pressure oil filter and fuel stop valve prior to entering the fuel pump. The type strainer housing contains a filter screen to remove any extraneous particulate residue left in the fuelnlines after installation. The strainer screen is to be removed after the initial 600 hours
of operation and the strainer housing must be cleaned and flushed upon removal of the screen prior to placing the turbine into service. Clean fuel is normally supplied to the turbine system ; however, during this initial period the low-pressure fuel strainer prevents contaminants from entering the fuel oil stop valve and the fuel pump, thereby preventing possible damage or improper functioning of these components.
Fuel Oil Stop Valve:
The fuel oil stop valve VSI is an emergency valve operated from the protection sys-tem used to shut off the supply of fuel to the turbine during normal or emergency shut downs. This stop valve is a special-purpose, hydraulically operated, two-position (open and closed) valve with a venturi disc and valve seat. When the turbine is shut down in the normal sequence, or by emergency trip operation, the fuel oil stop valve will fully close within a 0.5-second total elapsed time.
During normal operation of the turbine the stop valve is held open by high pressure
hydraulic oil (OH) that passes through a hydraulic trip relay (dump) valve VH4. This dump valve located between the hydraulic supply and the stop valve hydraulic cylinder, is hydraulically operated by trip oil (OLT) from the trip oil system. When the trip oil pressure is low (as in the case of normal or emergency shut-down), the dump valve spring shifts the valve spool to a position which dumps high pressure hydraulic oil (OH) in the stop valve actuating cylinder to the lube oil reservoir. The closing spring in the stop valve assembly then overcomes the oil pressure and closes the valve.
Fuel Oil Pump:
The fuel pump PFI is a positive displacement continuous output screw type pump
with two sets of opposed screws. The integral shaft screws are end mounted in roller bearings that are oil lubricated. The bearings and timing gears are supplied with lube oil from the main lube oil header and are sealed off from the fuel oil pumping chamber
GAS TURBINE (PG-9171E)
The pump is driven directly from the turbine driven accessory gear ; therefore, fuel
pump speed is directly proportional to turbine speed. The fuel pump discharge flow at any given turbine speed is greater than the turbine combustion requirements at that speed.
Liquid fuel pressure transmitter 96 FL-2 indicates that inlet fuel pressure is established. It is used as a permissive to energize the fuel pump clutch solenoid 20 CF-I. In case of loss of pressure while the turbine is running, 96 FL-2 will trip the turbine. An alarm 71 FP-1 or a trip 71 FP-2 are activated when appears a seal leakage on the main fuel pump.
Fuel pump discharge relief valve VR4
The fuel pump discharge relief valve, VR4, is located in a loop between the discharge and inlet of the pump. The valve prevents the fuel oil pressure from getting high
enough to rupture any lines in the event of a flow divider malfunction or freeze up. This valve is set to operate in the range of 1200 to 1300 psi and relieves back into the inlet pipe.
Fuel bypass valve
High pressure flow from the pump is modulated by the servocontrolled bypass valve assembly (VC3). Components of this assembly include the bypass valve body,
elec-trohydraulic servovalve 65 FP, and the hydraulic cylinder. This bypass valve is connected between the inlet and discharge sides of the fuel oil pump and meters the flow of fuel to the turbine by subtracting excess fuel delivered by the pump and bypassing it back to the pump inlet.
Servovalve 65 FP controls the bypass valve position according to the difference
Requirement and the sensed fuel flow. If the fuel requirement exceeds the actual oil flow, the bypass valve closes to increase the net oil flow to the turbine. The servo valve uses high pressure hydraulic oil (OH) (cleansed of contaminants by a metal filter FH3) to actuate the hydraulic cylinder and thus position the bypass valve.
High pressure fuel filters:
Fuel oil pump discharge pressure passes through the secondary (high pressure) fuel
filter FF 2-1 as it flows from the fuel pump to the flow divider. This full flow, high pressure filter helps to assure that contaminants and pipe scale are retained and prevented from entering the flow divider, thereby preventing possible damage or improper
