26GT 5-8 Compressor and Turbine Design Frame MS 9001 E Prepared by: Fazal-ur-Rehman Babar GT 5-8 27 1. GAS TURBINE DESIGN 1.1 G ENERAL ABOUT G AS T URBINE 5-8 GT 5-8 is a package power plant, as furnished for most installations, is comprised of the single-shaft, simple cycle, heavy duty gas turbine unit driving a generator. Fuel and air are used by the gas turbine unit to produce the shaft horsepower necessary to drive certain accessories, compressor and the generator. The turbine unit is composed of a starting device, support systems, an axial-flow compressor, combustion system components and a three-stage turbine. Both compressor and turbine are directly connected with an in-line, single-shaft rotor supported by three pressure lubricated bearings. The inlet end of the rotor shaft is coupled to an accessory gear having integral shafts that drive the fuel pump, lubrication pump, and other system components. 1.2 G AS T URBINE F UNCTIONAL D ESCRIPTION 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 17 stages of axial-flow compressor. For pulsation protection during start-up, the 11th stage extraction valves are opened and the variable inlet guide vanes are in the closed position. When the speed relay corresponding to 95 % (2850 rpm) speed actuates, the 11th stage extraction bleed valves close automatically and the variable inlet guide vane actuator energizes at 82 % speed to open the inlet guide vanes (I.G.V.) to (57°) the normal turbine operating position. Compressed air from the compressor flows into the annular space surrounding the 14 combustors, from which it flows into the spaces between the outer combustion casing (sleeve) and the combustion liners. The fuel nozzles introduce the fuel into each of the 14 combustors where it mixes with the combustion air and is ignited by both (or one, which is sufficient) of the two spark plugs. At the instant, one or both of the two spark plugs ignite their combustors, the remaining combustors are also ignited by crossfire tubes that connect the reaction zones of the combustors. After the rotor approaches 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 combustors expand into the 14 separate transition pieces attached to the aft end of the combustor 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 rotateable 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 bucket a portion of the kinetic energy of the jet is absorbed as useful work on the turbine rotor. Prepared by: Fazal-ur-Rehman Babar GT 5-8 Selective positioning of the wheels is made during assembly to reduce balance correction. two stub-shafts. air is confined to the space between the rotor and stator blades where it is compressed in stages by a series of alternate rotating and stationary airfoil-shaped blades. the air inlet of the gas turbine is the forward end. parts have to be made and assembled very accurately. the gases pass into the exhaust plenum. The forward and aft ends of each component are determined in like manner with respect to its orientation within the complete unit. Then. Forward stub-shaft is machined to provide the forward and aft thrust faces and the journal for the no. as well as the sealing surfaces for the no. compressor rotor and to drive certain accessories through accessory gear at various speeds. Included within the compressor casing are the inlet guide vanes. the rotor is dynamically balanced to a fine limit. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . Air is extracted from the compressor 5 th stage for bearing sealing and from 11th stage for pulsation control.1 C OMPRESSOR R OTOR The compressor rotor is an assembly of 15 individual wheels. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters in the following rotor stage at the proper angle.1 bearing oil seals and the compressor low-pressure air seals. 2. NOTE: By definition. a speed ring.1 bearing. tie bolts and the compressor rotor blades. the 17 stages of rotor and stator blades and the exit guide vanes. each with an integral wheel. 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. The rotor blades and spacers are inserted into these slots. After assembly.28 After passing through the third stage buckets. The RIGHT and LEFT sides of the turbine or of a particular component are determined by standing forward and looking aft. Each wheel and the wheel portion of each stub-shaft have slots broached around its periphery. The resultant shaft rotation is used to turn the generator rotor. In the compressor. thereby minimizing exhaust hood losses. COMPRESSOR The axial-flow compressor consists of the rotor and the enclosing casing. 2. while the exhaust end is the aft end. The compressed air exits through the compressor discharge casing to the combustion chambers. Since minimum clearance between rotor and stator provides best performance in a compressor. 2.2 Var i a b l e I n l e t G u i d e Van e s ( V I G V ) Variable inlet guide vanes are located at the aft end of the inlet casing. They support the rotor at the bearing points and constitute the outer wall of the gas-path annulus.2. The compressor stator blades are also airfoil shaped and are mounted by similar dovetails into ring segments.29 2. a separate casing that contains the № 1 bearing. in conjunction with the turbine shell and exhaust frame form the primary structure of the gas turbine. The control ring is positioned by a hydraulic actuator and linkage arm assembly.1 I n le t C a s i n g The inlet casing is located at the forward end of the gas turbine. to form both the inner and outer walls of the compressor diffuser and to join the compressor and turbine stators.3 F o r w a r d C a s i n g The forward compressor casing contains the first four compressor stator stages. It contains the final seven compressor stages.2.2. Its prime function is to uniformly direct air into the compressor. 2. Extraction ports in the casing permit removal of 5th and 11th stage compressor air. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . 2. The blades of first eight stages are attached to their wheels by dovetail arrangements. 2. 2.2 C OMPRESSOR S TATOR The stator (casing) area of the compressor section is composed of four major sections: - inlet casing forward compressor casing aft compressor casing compressor discharge casing These sections.4 A f t C a s i n g The aft compressor casing contains the 5th through 10th compressor stages. The position of these vanes has an affect on the quantity of compressor air flow. 2. They also provide support for bearing № 2. This air from 5 th stage is used for cooling and sealing functions and 11th stage air is extracted for starting and shutdown surge and pulsation control. 2. Locking keys also hold them in place. The inlet casing also supports the no. the forward end of the combustion wrapper and the inner support of the first-stage turbine nozzle. Movement of these guide vanes is accomplished by the inlet guide vane control ring that turns individual pinion gears attached to the end of each vane.3 C OMPRESSOR R OTOR B LADES The compressor rotor blades are airfoil shaped and designed to compress air efficiently at synchronous speed.1 bearing housing.2.5 D i s c h a rge C a s in g The compressor discharge casing is the final portion of the compressor section. The stator blades of the last nine stages and two exit guide vanes have a square base dovetail that are inserted directly into circumferential grooves in the casing. It is the longest single casting consists of two cylinders. the compressor is bound to run at speeds below the permissible value. The variable inlet guide vane actuator is a hydraulically actuated assembly having a closed feedback control loop to control the guide vanes angle. 4 . H OW C OMPRESSOR S URGE IS A VOIDED ? For pulsation protection during start up. During startup and shutdown of a gas turbine. 1 C o n t r o l t h r o u g h I n l e t G u i d e Van e s Variable inlet guide vanes (VIGV) are installed on the compressor to provide compressor pulsation protection during start-up and shutdown and also to be used during operation under partial load conditions. the variable inlet guide vanes (VIGV) are in closed position and the 11th stage extraction bleed valves are open. air will have to be blown off at specific parts of the compressor as a result of which the volume flow is matched to the blade case cross-sections. the 11th stage extraction bleed valve close automatically and variable inlet guide vane actuator energises to open the inlet guide vanes (IGV) to the normal turbine operating position. simply because the shape and position of the blades is not conducive to low speed and low flow conditions.4 C OMPRESSOR S URGE Operating speed of the gas turbine is held constant and very little deviation takes place. Since on start-up and shut-down of the gas turbine and under-frequency operation. Such separation will cause the delivery to become unstable. or to the control system pulsation protection limits during the start-up and shut-down sequences. this is. The vanes are automatically positioned within their operating range in response either to the control system exhaust temperature limits for normal loaded operation. The compressor will begin to surge. the air is not smoothly compressed. Speeds less than the permissible range would exert strain on the front stages of the compressor that the result would be separation of the flow at the airfoils. the rotor and stator blades do not deliver a smooth progression of air through the compressor. This is characterised by rapid fluctuations of the compressor discharge pressure combined with heavy vibration of the unit and surging noise in rhythm with the pressure fluctuations with the compressor blades being endangered by the resulting high alternating bending stresses and high temperatures. When the speed relay corresponding to 95 % speed actuates. To achieve a good performance. Figure illustrates the effects of air flow through a gas turbine compressor during a compressor surge. the angle and aerofoil shape of the rotor and stator blades are precisely machined and set in place such that the compression of air through the compressor is smooth and efficient. The blades of the axial compressor are designed to achieve optimum efficiency at the synchronous speed.30 2. 2 . Prepared by: Fazal-ur-Rehman Babar GT 5-8 . This occurs. Pneumatically operated air extraction bleed valves. controlled by a three-way solenoid valve. CAUTION: Under no circumstances should attempts be made to start the turbine if all four extraction bleed valves are not fully opened. -3 and -4 are mounted on the valves to give an indication of valve position. Prepared by: Fazal-ur-Rehman Babar GT 5-8 .4. by means of a continuous blow-down orifice. Eleventh stage air is extracted from the compressor at four flanged connections on the compressor casing. VA 2-1. -3 and -4 to the turbine exhaust plenum. speed and flow characteristics of the gas turbine compressor are such that air must be extracted from the 11th stage and vented to atmosphere to prevent pulsation of the compressor during the acceleration period of the turbine starting sequence and during deceleration of the turbine at shut-down. piston-operated.31 2. -2. 33 CB-1 through -4. Air from compressor discharge is piped to a porous air filter which removes dirt and water from the compressor discharge air. before the air enters solenoid valve 20 CB. the air is piped to the piston housings of the four extraction valves. are used to accomplish the pulsation protection. Each of these connections is piped through a normally open (by spring force). Limit switches. When a turbine shut-down signal is initiated and the generator circuit breaker is opened. Limit switches 33 CB-1. From the solenoid valve. Compressor discharge air controlled by solenoid valve 20 CB is used to close the compressor bleed valves. Serious damage to the compressor blades may occur if all the valves are not opened during the accelerating and decelerating cycle of the gas turbine. 20CB is de-energized and 11th stage air is again discharged into the exhaust plenum to prevent compressor pulsation during the turbine shut-down period. on the valves provide permissive logic in the starting sequence and ensure that the extraction valves are fully opened before the turbine is fired. butterfly valve. 20 CB is de-energized and the 11th stage extraction valves are open allowing 11th stage air to be discharged into the exhaust plenum thereby eliminating the possibility of compressor pulsation. -2. The turbine accelerates to 95% speed and then the 20CB solenoid valve is energized to close the extraction valves and allow normal running operation of the turbine. During turbine start-up.2 S u r ge C o n t r o l t h r o u g h B l e e d Val v e s The pressure. All 14 combustion liners.32 3. This system also includes fuel nozzles. flame detectors and crossfire tubes. High pressure air from the compressor discharge is directed around the transition pieces and into the combustor liners. Hot gases. The hot combustion gases from the reaction zone pass through a thermal soaking zone and then into a dilution zone where additional air is mixed with the combustion gases. generated from burning fuel in the combustors. 1- Combustion Wrapper: The combustion wrapper forms a plenum in which the compressor discharge air flow is directed to the combustors. flow sleeves and transition pieces are identical. The air flows upstream along the outside of the combustion liner toward the liner cap. COMBUSTION SECTION The combustion system is of the reverse-flow type with 14 combustors arranged around the periphery of the compressor discharge casing. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . spark plug ignition system. Transition pieces direct the hot gases from the liners to the turbine nozzles. In turn. through metering holes in both the cap and liner and through combustion holes in the forward half of the liner. are used to drive the turbine. the wrapper is supported by the compressor discharge casing and the turbine shell. Metering holes in the dilution zone allow the correct amount of air to enter and cool the gases to desired temperature. Fuel is supplied to each combustor through a nozzle designed to disperse and mix the fuel with the proper amount of combustion air. Combustor Liner GT 5-8 2- Combustors: Discharge air from the axial-flow compressor flows into each combustion flow sleeve from the combustion wrapper (see figure). Its secondary purpose is to act as a support for the combustor’s assemblies. Combustors are numbered counterclockwise when viewed looking down-stream and starting from the top of the machine. This air enters the combustor’s reaction zone through the fuel nozzle swirl tip. 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 as shown in figure. This air enters the combustion zone through metering holes for proper fuel combustion and through slots to cool the combustor liner. If flame is present.054" (1. The gas within this flame sensor detector is sensitive to the presence of ultraviolet radiation which is emitted by a hydrocarbon flame. a spark at one or both of these plugs ignites the gases in a chamber. Once a flame is established in one combustor. These springinjected and pressure-retracted plugs receive their energy from ignition transformers at 13 KV.000" (0. 12 and 13. a flame monitoring system is used consisting of four sensors which are installed on four combustors no. After the establishment of flame.33 3- Crossfire Tubes: All fourteen combustors are interconnected by means of crossfire tubes. and an electronic amplifier which is mounted in the turbine control panel. the ionization of the gas in the detector allows conduction of current in the circuit which activates the electronics to give an output defining flame. the difference of pressure existing between a fired combustor basket and an unfired one. chamber pressure causes the spark plugs to retract and the electrodes are removed from the combustion zone. shut down the turbine. etc. is impressed across the detector terminals. 4- Spark Plugs: Combustion is initiated by means of the discharge from two high-voltage retractable electrode spark plugs installed in adjacent combustors no. 4. the absence of flame will generate an opposite output defining "no flame". Retaining Nut Lock Plate Insulator Gasket Top Cover Tie Bolt 4.00 mm) Figure CI-40 Spark Plug Assembly 5- Flame Detectors: During the starting sequence. 3. the remaining chambers are ignited by crossfire through the tubes that interconnect the reaction zone of the remaining chambers. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . The ultraviolet flame sensor consists of a flame sensor.37 mm) 0. if voltage is re-established to the sensors defining the loss (or lack) of flame a signal is sent to a relay panel in the turbine electronic control circuitry where auxiliary relays in the turbine firing trip circuit. Conversely. The “Failure to Fire” or “Loss of Flame” is also indicated on the annunciator.01" (0. For this reason. If a loss of flame is sensed by two flame detector sensor. it is essential that an indication of the presence or absence of flame be transmitted to the control system. supplied by the amplifier. containing a gas filled detector. 5 and 11.5" (114 mm) Stroke Terminal Extension Spring Cylinder Piston / Rod Assembly Spark Plug Washers Core Assembly Equal Gaps within 0. A dc voltage. As rotor speed increases. is enough to cause a temporary flame through the crossfire tube which fires the combustor basket unfired. the control circuitry will cause an annunciation only of this condition. At the time of firing.25 mm) 0. starting means circuit. The liquid fuel and atomizing air enter the fuel nozzle assembly through separate connections. in a manner which promotes uniform. they are introduced through separate but concentric passages in the nozzle body. Normally its position is towards sump tank and any leakage of liquid fuel oil goes towards sump tank. VA 17-2 & VA 17-5 Water to washing pit The false start drain valves. Therefore. Purge Air Fuel Gas GCV Gas Control Valve SRV Speed Ratio Valve Combustion Air Gas outlet Purge air VCK-2 Atomizing Air HSD or Furnace Oil VCK-1 Liquid Fuel Drain Liquid Fuel Inlet To Sump Tank Combustion Air Atomizing air Atomizing air is utilized with liquid fuel to assist in the formation of a finely divided spray. turbine area (VA 17-2) and lower part of the turbine exhaust frame (VA 17-3). Prepared by: Fazal-ur-Rehman Babar GT 5-8 . for safety reasons in the event of an unsuccessful start. rapid and complete combustion. these valve are opened at start and closed at about 35-40% speed. Thus. When GT is started. Fuel enters the inner passage. Air pressure from the axial-flow compressor discharge is used to actuate these valves. the valves open as compressor speed drops (compressor discharge pressure is reduced). False start drain valve is a three way valve. Fuel burning process completes within combustor liner zone and flame finishes after the liner. During the turbine shut-down sequence. The transition pieces are sealed to both the outer and inner sidewalls on the entrance side of the nozzle. 7- Transition Pieces Transition pieces direct the hot gases from the liners to the turbine first stage nozzle. Then.34 6- Fuel Nozzles: Each combustor is equipped with a fuel nozzle that emits the metered amount of the required fuel into the combustion liner. From turbine drains Compressor discharge air Oil to sump tank False start drain valves VA 17-1. During turbine washing their position is changed towards washing pit and water goes to washing pit. The fuel nozzle functions to distribute the liquid fuel into the reaction zone of the combustion liner. After completion of washing three way valve’s position is again changed towards sump tank. Atomizing air enters around the fuel nozzle and split fuel into very fine particles. normally open. are closed during start-up when the turbine speed reaches a sufficient value. the accumulation of combustible fuel oil is drained through false start drain valves provided at appropriate low points in the combustion wrapper (VA 17-1). 8- False Start Drain In liquid fuel units. only flue gas enters into the transition piece. In this way fuel ignites easily and burns completely. the first nozzle area is divided into 14 equal areas receiving the hot gas flow. so minimizing leakage of compressor discharge air into the nozzles. In the reactive design. but more important is that. Turbine section components include. 2 bearing is a part of the wheel shaft. Therefore. second and third-stage turbine wheels with buckets. expansion process takes place only through the fixed nozzles. For an impulse turbine less number of stages are required for a given output. GT 5-8) have impulse airfoil shape at the root and progressively reactive airfoil shape at their top (see Figure). therefore. It includes the no. is converted to mechanical energy. TURBINE SECTION The three stage turbine section (Fig-2) is the area in which energy in the form of high pressurized gas. it permits high operating temperature for a given bucket life. produced by the compressor and combustion sections. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . 3 bearing journal. the blade’s foil shape is 50% impulse and 50% reaction. The wheels are held together with through bolts. The aft wheel shaft connects the third-stage turbine wheel to the load coupling.35 4. The turbine buckets in MS 9001 E (3 stages. In a pure impulse turbine. expansion takes place both at fixed nozzles and rotating buckets.1 T URBINE R OTOR The turbine rotor assembly consists of two wheel shafts. two turbine spacers and three bearings. Rotor Blades or Buckets: The turbine buckets increase in size from the first to third-stage. In all heavy duty "General Electric Company" gas turbines high energy "impulse" turbines are used as contrasted with lower energy "reactive" design. the first. The journal for the no. turbine rotor turbine shell nozzles shrouds exhaust frame exhaust diffuser 4. The hot gas mixture coming from the combustion system is guided towards the first stage nozzle through transition pieces which provide an as uniform as possible circumferential hot gas flow distribution to the first stage turbine nozzle. the bucket size must be increased to accommodate the gas flow. Each turbine stage is comprised of a nozzle and the corresponding wheel with its buckets. Flue gas pressure is decreased due to energy conversion in each stage. The forward wheel shaft extends from the first-stage turbine wheel to the aft flange of the compressor rotor assembly. These shrouds interlock from bucket to bucket to provide vibration damping. the tips of these buckets. This is important for the turbine life because of thermal stresses. where kinetic energy is converted to mechanical energy. Air is introduced into each first-stage bucket through a plenum at the base of the bucket dovetail. temperature on turbine first nozzle must not exceed 1004 °C. The third-stage buckets are not internally air cooled. like the second-stage buckets. Since the lower temperatures surrounding the bucket shanks do not require shank cooling.36 Temperature at first stage nozzle is controlled by the gas turbine control system by means of controlling the hot gas temperature in the exhaust casing. are enclosed by a shroud which is a part of the tip seal. At base load operation. the second-stage cooling holes are fed by a plenum cast into the bucket shank. The hot gas stream expands through the first stage nozzle and it leaves with a whirl to attack the first stage turbine wheel. This process is repeated in the other turbine stages. Each first-stage bucket contains a series of longitudinal air passages for bucket cooling. The holes are spaced and sized to obtain optimum cooling of the airfoil with minimum compressor extraction air. Spanwise holes provide cooling air to the airfoil at a higher pressure than a design with shank holes. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . Like the first-stage buckets. This increases the cooling effectiveness in the airfoil so airfoil cooling is accomplished with minimum penalty to the thermodynamic cycle. It flows through cooling holes extending the length of the bucket and exits at the recessed bucket tip. the second-stage buckets are cooled by spanwise air passages the length of the airfoil. Turbine Rotor Cooling: The first-stage buckets are the first rotating surfaces encountered by the extremely hot gases leaving the first-stage nozzle. Hot gases contained by the turbine shell are a source of heat flow into the shell. This area is called the wheel-space. The 3rd aft wheel-space is cooled by cooling air that exits from the exhaust frame cooling circuit. 2.37 The turbine rotor must be cooled to maintain reasonable operating temperatures and. bearing no. into the main gas stream. To control the shell diameter. therefore. Air extracted through the rotor. 14:00 hrs. Flow through these passages is generated by frame blower cooling fans 88 TK 1. Thermocouple No. This air also maintains the turbine wheels. rd Temp 397 °C 3 ST FWD WS OUT TTWS 3F01 366 °C 352 °C 3rd ST FWD WS OUT TTWS 3F02 386 °C rd 360 °C 3 ST FWD WS OUT TTWS 3A01 292 °C 356 °C 3rd ST FWD WS OUT TTWS 3A02 338 °C The turbine rotor is cooled by means of a positive flow of relatively cool air (300 °C. Six thermocouples are at stage-1. assure a longer turbine service life. ahead of the compressor 17th stage. turbine spacers and wheel shaft at approximately compressor discharge temperature to assure low steady state thermal gradients thus ensuring long wheel life. The turbine nozzles. There are 14 thermocouples before and after the nozzles to measure the wheel-space temperature. 05/02/08. Compressor inlet temperature 14 °C and Compressor discharge temperature 330°C. st 1 ST FWD WS IN TTW SIF/1 1st ST FWD WS IN TTW SIF/2 st 1 ST FWD WS OUT TTW SIF01 1st ST FWD WS TTW SIF02 st Temp Thermocouple No. shrouds. Heat flow limitations incorporate insulation.3 and turbine exhaust diffuser are internally supported from these components. is used for cooling the 1st and 2nd stage buckets and the 2nd stage aft and 3rd stage forward rotor wheel spaces. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . 4. This positioning is critical to gas turbine performance. The external surface of the shell incorporates cooling air passages. It determines turbine clearances and the relative positions of the nozzles to the turbine buckets. it is important that shell design reduces the heat flow into shell and limits its temperature. 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. Turbine Shell The turbine shell controls the axial and radial positions of the shrouds and nozzles.2 T URBINE S TATOR The turbine shell and the exhaust frame constitute the major portion of the gas turbine stator structure. four are at stage-2 and four are at stage-3. relative to hot gas path air) extracted from the compressor. dt. The 1st stage aft and 2nd stage forward wheel spaces are cooled by compressor discharge air that passes through the first stage shrouds and then radially inward through the stage 2 nozzle vanes. cooling and multilayered structures. nd 350 °C 2 ST FWD WS OUT TTWS 2F01 391 °C 2nd ST FWD WS OUT TTWS 2F02 nd 341 °C 2 ST AFT WS OUT TTWS 2A01 356 °C 2nd ST AFT WS OUT TTWS 2A02 1 ST FWD WS TTW SIA01 400 °C 1st ST FWD WS OUT TTW SIA02 369 °C Temp Thermocouple No. Following wheel-space reading are taken from log sheet of GT-5. The 1st stage forward wheel-space is cooled by air that passes through the high pressure packing seal at the aft end of the compressor rotor. The transition pieces are sealed to both the outer and inner sidewalls on the entrance side of the nozzle.38 Turbine Nozzles In the turbine section there are three stages of stationary nozzles (see figure). The aft outer diameter of the retaining ring is loaded against the forward face of the firststage turbine shroud and acts as the air seal to prevent leakage of compressor discharge air between the nozzle and shell. The nozzle consists of 16 cast segments. It is held at the outer sidewall forward and aft sides in grooves in the turbine shrouds in a manner Prepared by: Fazal-ur-Rehman Babar GT 5-8 . The nozzle segments are held in a circumferential position by radial pins from the shell into axial slots in the nozzle outer sidewall. resulting from changes in temperature while the ring remains centred in the shell. Second-stage nozzle is cooled with compressor discharge air. 2 airfoils 16 Segments. This close fitting tongue-and-groove fit between nozzle and shrouds acts as an outside diameter air seal. The male hooks on the entrance and exit sides of the outer sidewall fit into female grooves on the aft side of the first-stage shrouds and on the forward side of the second-stage shroud. are contained by a horizontally split retaining ring which is centreline supported to the turbine shell on lugs at the sides and guided by pins at the top and bottom vertical centrelines. Third-Stage Nozzles The third-stage nozzle receives the hot gas as it leaves the second-stage buckets. this minimizes leakage of compressor discharge air into the nozzles. This permits radial growth of the retaining ring. there are seals at both the inside and the outside diameters to prevent loss of system energy by leakage. First-stage nozzle is cooled with compressor discharge air. each with three partitions or airfoils. each with two partitions of airfoils. This nozzle is made of 16 cast segments. increases its velocity by pressure drop. to maintain the nozzle concentric with the turbine shell and rotor. in the hot combustion gas flow. 4 airfoils First-Stage Nozzles The first-stage nozzle receives the hot combustion gases from the combustion system via the transition pieces. Second-Stage Nozzle Combustion air exiting from the first-stage buckets is again expanded and redirected against the second-stage turbine buckets by the second-stage nozzle. which direct the high-velocity flow of the expanded hot combustion gas against the turbine buckets causing the turbine rotor to rotate. Because of the high pressure drop across these nozzles. The 18 cast nozzle segments. they are subjected to thermal stresses in addition to gas pressure loadings. 3 airfoils 16 Segments. 18 Segments. each with four partitions or airfoils. and directs this flow against the third-stage buckets. Since these nozzles operate. Shrouds Unlike the compressor blading. due to which it can take more load. The third-stage nozzle is circumferentially positioned by radial pins from the shell.3 is supported from the inner cylinder. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . To compensate this misalignment bearing no. The exhaust frame assembly consists of the exhaust frame and the exhaust diffuser. the turbine bucket tips do not run directly against an integral machined surface of the casing but against annular curved segments called turbine shrouds. 4. Joints between shroud segments are sealed by interconnecting tongues and grooves. the shell roundness is maintained and important turbine clearances are assured. this results in higher turbine efficiency. the shell cooling load is drastically reduced. when turbine rotor becomes hot then it becomes high. The exhaust frame is bolted to the aft flange of the turbine shell. 4. The shroud segments are maintained in the circumferential position by radial pins from the shell. Diaphragms Attached to the inside diameters of both the second and third-stage nozzle segments are the nozzle diaphragms (see figure at previous page). the shell diameter is controlled. 3 has special arrangement of tilting pads. These diaphragms prevent air leakage past the inner sidewall of the nozzles and the turbine rotor. The turbine shrouds' secondary function is to provide a high thermal resistance between the hot gases and the comparatively cool shell. at normal load the hot gas temperature is still high at about 500 °C for the gas turbines 5-8.3 R OTOR A LIGNMENT Generator rotor is 1. The bearing no.25 mm above than turbine rotor. The high/low. In simple cycle. Minimal radial clearance between stationary parts of diaphragm and nozzles and the moving rotor are essential for maintaining low interstage leakage. The shrouds' primary function is to provide a cylindrical surface for minimizing bucket tip clearance leakage.4 E XHAUST F RAME AND D IFFUSER On exhaust. By accomplishing this function. labyrinth seal teeth are machined into the inside diameter of the diaphragm. exhaust system opens in ambient atmosphere through a duct assembly comprising filter and silencer. the frame consists of an outer cylinder and inner cylinder interconnected by ten radial struts. They mate with opposing sealing lands on the turbine rotor. The inner gas path surfaces of the two cylinders are attached the inner and outer diffusers. After GT start. Structurally.39 identical to that used on the second-stage nozzle. The oil flows through branch lines to an inlet in each bearing housing. All bearings are pressure-lubricated by oil supplied from the main lubricating oil system. 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 wheel-space. BEARINGS The MS 9001 E gas turbine unit 5-8 contain three main journal bearings used to support the compressor-turbine rotor. Bearing metal temperature detectors have been installed on all bearings. the exhaust frame. 5. At the exit of the diffuser. These struts position the inner cylinder and bearing № 3 in relation to the outer casing of the gas turbine. and one in the exhaust frame. Exhaust frame radial struts cross the exhaust gas stream. bolts to. Class Type Vibration Pick-ups 1 Journal Elliptical BB-1 / BB-2 1 Loaded Thrust Self-Aligned (Equalized) 1 Unloaded Thrust Tilting Pad 2 Journal Elliptical BB-3 3 Journal Tilting Pad BB-4 / BB-5 4 Journal BB-7 / BB-8 5 Journal BB-9 Prepared by: Fazal-ur-Rehman Babar GT 5-8 . Turbine shell cooling air enters the space between the exhaust frame and diffuser and flows in two directions. Gases exhausted from the third turbine stage enter the diffuser where velocity is reduced by diffusion and pressure is recovered. BEARINGS No. The struts must be maintained at a uniform temperature in order to control the centre position of the rotor in relation to the stator. turning vanes direct the gases into the exhaust plenum. These bearing assemblies are located in three housings: one at the air inlet.stator axial position.2 into this space around the struts. The exhaust frame is a fabricated assembly consisting of an inner cylinder and an outer divergent cylinder that flares at the exit end at a right angle to the turbine centreline. located at the extreme aft end of the gas turbine. High temperature alarm limit is 130 °C. The unit also includes thrust bearings to maintain the rotorto.40 The exhaust diffuser. and is supported by. 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 from 88 TK 1. At the exit end of the diffuser between the two cylinders are five turning vanes mounted at the bend. one in the compressor discharge casing. Oil Vent Some of the sealing air returns with the oil to the main lubricating oil reservoir and is vented through a lube oil vent.41 Lubrication The three main turbine bearings are pressure-lubricated with oil supplied by the 12. 5. thus eliminating a potential safety hazard. Oil is prevented from escaping along the turbine shaft by labyrinth seals. The upper half of the bearing housing can be removed for bearing liner inspection without the removal of the upper half inlet casing. Labyrinth seals at each end of the housing are pressurized with air extracted from 5th stage of the compressor. A vent pipe takes air from the tank and an air nozzle or venturi sucks air from the lube oil tank. The floating ring seal and a double labyrinth seal at the forward end of the thrust bearing cavity are to contain oil and to limit entrance of air into cavity. The oil seals are designed with two rows of packing and an annular space between them. is run within the lube oil reservoir drain line. (1) (2) (3) active (loaded) thrust bearing inactive (unloaded) thrust bearing journal bearing Additionally. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . where practical. A smooth surface is machined on the shaft and the seals are assembled so that only a small clearance exists between the oil and seal deflector and the shaft. as a protective measure. it flows into an annulus around the bearing liner. it contains a floating ring or shaft seal. or drain channels.540 litres capacity lubricating oil reservoir. These labyrinth packings and oil deflectors (teeth type) are assembled on both sides of the bearing assemblies where oil control is required. Blower fan 88FX-1 provides air to the venturi. The components are keyed to the housing to prevent rotation. When the oil enters the bearing housing inlet. Pressurized sealing air is admitted into this space and prevents lubricating oil from spreading along the shaft. The lower half of the bearing assembly supports the forward stub shaft of the compressor rotor. This procedure is referred to as double piping and its rationale is that in the event of a pipe-line leak.1 B EARING №. From the annulus the oil flows through machined slots in the liner to the bearing surface. labyrinth seals and a housing in which the components are installed. oil will not be lost or sprayed on nearby equipment. Oil Seals Oil on the surface of the turbine shaft is prevented from being spun along the shaft by oi1 seals in each of the three bearing housings. 1 (J OURNAL & T HRUST B EARING ) The № 1 bearing assembly is located in the centre of the inlet casing assembly and contains three bearings. This support includes ledges on the horizontal and an axial key at the bottom centre line. The № 1 bearing assembly is centre-line supported from the inner cylinder of the inlet casing. Oil feed piping. 3 B EARING №. 3 (J OURNAL B EARING WITH T ILTING P ADS ) The № 3 bearing assembly is located at the aft end of the turbine shaft in the centre of the exhaust frame assembly. The № 2 bearing is located in a pressurized space between the compressor and the turbine. they are free to move in two directions. The space between the two other seals is cooled by air extracted from the 5th compressor stage. which make them capable of tolerating both offset and angular shaft misalignment. five labyrinth seals and a bearing housing. These converging passages generate a high-pressure oil film beneath each pad. Air flows through this seal into the drain space of the housing and is vented outside the machine via the inner pipe connecting to the bottom of the housing. The clamping action helps maintain shaft stability. 5. The middle labyrinth prevents the hot air leakage from mixing with the oil.42 5. This drain space vent piping continues to the lubricating oil tank. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . It consists of a tilting pad bearing. Because the pads are point-pivoted. and air leaks through the outer labyrinth at each end of the housing.2 B EARING №. This support includes ledges on the horizontal and an axial key at the bottom centre-line permitting relative growth resulting from temperature differences while the bearing remains centred in the discharge casing. This assembly includes three labyrinth seals at both ends of the housing. 2 (J OURNAL B EARING ) The № 2 bearing assembly is centre-line supported from the inner cylinder of the compressor discharge casing. The mixture of hot air and cool air is vented outside the unit via the outer pipe connected at the top of the bearing housing. The lower half of the bearing assembly supports the forward wheel shaft of the turbine rotor assembly. The individual pads are assembled so that converging passages are created between each pad and the bearing surface. which produces a symmetrical loading or "clamping" effect on the bearing surface. This pin locates the bearing within its housing and serves to prevent the bearing from rotating with the shaft. 415 V. 750 rpm GT 5-8 . 3. Couplings are of two types. The retainer ring serves to locate and support the pads. 6. STARTING SYSTEM Before the gas turbine can be fired and started it must be rotated or cranked by accessory equipment. The coupling is designed to transmit the starting and driving torque of starting motor and turning gear as well as to provide flexibility to accommodate nominal misalignment and axial movement of the turbine rotor relative to the accessory gear box. operating through a torque converter to provide the cranking torque for speed required by the turbine for start-up. 415 V. There are three types of misalignment that is accommodated by the coupling: angular. This is accomplished by an induction motor. hollow coupling connects the turbine rotor shaft to the generator rotor. 7. A bolted flange connection forms the joint at each end of the coupling. Upper half with tilting pads 6. It is a horizontally split member that contains the pad support pins.43 The tilting pad journal bearing comprises two major components pads and a retainer ring. The starting system consists of: Starting motor induction type Torque Converter: Voith Germany Torque Adjusting Motor Turning Gear Motor Prepared by: Fazal-ur-Rehman Babar 88 CR Voith 88 TM 88 TG 1000 kW. The support pins and shims transmit the loads generated at the pad surfaces and are used to set the bearing clearance. An anti rotation pin extends from one edge of the lower half of the rectangular ring. rigid and flexible. parallel and a combination of both. 2820 rpm 30 kW. 6. 2975 rpm 0. Bearing No. adjusting shims.5 kW. COUPLINGS Couplings are used to transmit starting torque from the accessory gear to the gas turbine axial compressor and to transmit shaft horsepower from the turbine to the driven generator.2 A CCESSORY G EAR C OUPLING An oil filled flexible coupling is used to connect the accessory drive to the gas turbine shaft at the compressor end. 6600 V.1 L OAD C OUPLING A rigid. oil feed orifice and oil discharge seals. That means. warm up. Due to great difference of speeds at the beginning of the start up sequence (Cranking motor 2975 rpm. when speed decreases to 99 rpm. These vanes. Control of the torque converter is achieved via a solenoid valve 20 TU-1 and a hydraulically operated dump valve. the torque converter is filled with oil. the torque converter is equipped with a range of variable vanes.44 7. Starting motor is linked to an impeller called pumpwheel. the torque converter motor sets it to 11 turns and a turning motor 88 TG specially provided to rotate the turbine for cooldown purpose starts. The main parts of the torque converter are the impeller driven by the input shaft. the oil transmits the power. extracted from lube oil circuit at 6.9 bar by energizing solenoid valve 20 TU-1. acceleration. admit circulation of certain oil flow corresponding to their position.1 T ORQUE C ONVERTER A motor driven torque adjustor drive 88 TM. Pump-wheel transforms the power of the cranking motor into a manometric lift (i. washing etc. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . The turbine-wheel transforms this manometric lift into a rotating power and transmits it to the turbine shaft. Two seconds after the start up of cranking motor. the turbine wheel which drives the output shaft and the stator which directs fluid from the impeller to the turbine at the correct angle to produce the required output torque. To adjust various speed limits for turning. turbine shaft 120 rpm) torque converter transmits a very high torque to the turbine shaft and thus breaks it away. provides the means for adjusting torque output within specified ranges. The pump-wheel and turbine-wheel do not have any mechanical contact. increase in pressure) of oil. Then speed is increased and turning speed value is about 120 rpm. That means. The turbine shaft is linked to a turbine-wheel. start up. installed in converter housing. automatically operated by the torque adjusting motor or manually by a hand-wheel drive.e. output speed is limited by reducing the output power through variable vanes. After a shut down order. A crank and restart can be initiated at any time below 14 HT speed (at turning gear).45 The torque adjustor drive 88 TM rotates the blades of the impeller. When the impeller blades are fully closed there is no transfer of torque and when blades are fully open maximum torque is transferred. fluid is admitted into the torque converter hydraulic circuit from the lubrication system by the integral valve 20 TU-1 two seconds after the starting motor 88 CR is energized. the internal geometry of the torque converter is adjusted to 3 turns by the torque adjustor drive 88 TM to hold firing speed constant throughout the firing and warm-up cycle. but if does not drained then indication “Torque Converter drain valve trouble” is appeared on the screen and the m/c would take shut down command. The operator turns the operation selector switch 43 of the turbine control panel to position TURNING.1 F u n c ti o n a l De s c r ip ti o n o f Tor q u e C o n ve r t e r 1. Solenoid valve 20 TU-1 is energized and the torque is adjusted to 11 turns allowing to turn the turbine at a speed of about 120 rpm for cool down purposes after shut down. the turning motor 88 TG starts. NOTE: Torque Converter is drained at 60 % speed by opening the 20 TU-1 solenoid valve. The speed decreases a little and at about 99 rpm. Torque converter is readjusted at 11 turns and it allows a turning speed of about 120 rpm. The turbine begins to increase in speed and continues to accelerate until firing speed is attained and relay 14 HM picks up. When the turbine has reached this speed (14 HM setpoint). (about 60 % speed). Start-up In the normal starting sequence. to limit the torque in case of malfunction of the system For high torque limit 7. which effects disconnect. then gives a START order. turning motor 88 TG starts. motor 88 CR is stopped. at the same time cranking motor 88 CR is deenergized. The starting motor 88 CR starts. by deenergizing solenoid valve 20 TU-1. the torque converter hydraulic circuit is drained. When the speed reaches about 120 rpm. Shut-down The shut-down order is given and the turbine speed slows down. 2. Torque converter is adjusted at 22 turns to achieve maximum torque of the starting motor. Readjustment of the converter geometry (torque adjustment) at the end of warm-up allows the torque converter to assist in accelerating the unit up to self sustaining speed.1. The number of turns. 33 TM-1 33 TM-2 33 TM-3 33 TM-4 Adjusted at 6 turns Adjusted at 3 turns Adjusted at 11 turns Adjusted at 22 turns 33 TM-5 Adjusted at 0 turns 33 TM-6 Adjusted at 30 turns Washing speed Minimum firing torque for warm up Turning gear operation To obtain the maximum torque. during accelerating phase upto 60 % speed For minimum torque limit. depends on the operation of limit switch. Six switches are provided for torque adjustment. as it can be seen from the top of torque converter. 3. 20 TU-1 is energized and torque converter is adjusted to 22 turns. When relay 14 HP drops out (at about 99 rpm). At this speed. Turning The turbine is at standstill and all circuits are ready for turning. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . is a gearing assembly.46 8. Accessories driven by the gear include: The main lube oil pump The main hydraulic supply pump The liquid fuel pump and The main atomizing air compressor The speeds and functions of shafts are: Shaft 1: Shaft 2: Shaft 3A: Shaft 3B: Shaft 4: 3000 rpm 3424.2 rpm 6607. Connect and disconnect the turbine by its starting motor. Contained within the gear casing are the gear trains which provide the proper gear reductions to drive the accessory devices at the required speed.2 rpm 1421. ACCESSORY DRIVE The function of the accessory gear in this system is to drive a number of the control components and to provide connection between the starting motor and the gas turbine compressor. with the correct torque values. Location of air ejector Automizing air compressor shaft TURBINE SIDE Main Oil Pump Fuel Pump Driving shaft Mechanical Overspeed Main HP Oil Pump The accessory drive gear.2 rpm 1554. located at the compressor end of the gas turbine. It is permanently coupled to the turbine compressor shaft by a flexible coupling. Its functions are to: Drive accessories of gas turbine at proper speed. In addition it contains the turbine overspeed bolt and trip mechanism.9 rpm Prepared by: Fazal-ur-Rehman Babar Driving shaft A tachometer on turbine side Fuel pump through electromagnetic clutch It drives atomizing air compressor HP hydraulic oil pump on starting motor side and Lube oil pump on turbine side GT 5-8 . The overspeed bolt which actuates the trip upon overspeed is installed in the main shaft. it is divided into various compartments/ enclosures. in the compact integrated gas turbine-generator design. the sequence being broken by the inlet plenum and the exhaust plenum. Doors are kept tightly closed by sturdy latches. Gaskets between panels and framing maintain a weather-tight condition. They are provided with thermal and acoustical insulation and lighted for convenience. 9. Lubrication of the gear is from the turbine’s pressurized bearing header supply. referred to as compartments. there is an in-line sequence of lagged compartments. capable of mechanically dumping the oil in the trip circuits. Inspection and maintenance are facilitated as the door panels allow easy access for station personnel and the removable panels provide greater accessibility for major inspections and overhauling. are those partitioned areas in which specific components of the overall power plant are contained. These compartments are built for all weather conditions and designed for accessibility when performing maintenance. Compartment construction includes removable panels. These compartments are named as: 12345- Accessory compartment Turbine compartment Exhaust compartment Load coupling compartment Generator compartment Prepared by: Fazal-ur-Rehman Babar Exhaust Compartment Load Coupling Compartme nt Generator Compartment Turbine Compartment Accessory Compartment GT 5-8 . COMPARTMENTS / ENCLOSURES Gas Turbine 5-8 is a package type unit. is mounted on the exterior casing of the gear. This device can shut the turbine down when the speed exceeds the design speed. Thus. Gas turbine enclosures. hinged doors and a thermally insulated roof section with welded frame structuring providing the support for these parts.47 A high-pressure turbine overspeed trip. The panels are thermally insulated and held in place with bolts. There is an inlet plenum between the accessory and the turbine compartments and an exhaust plenum between the turbine and generator compartments. Atomizing air system Gas system. starting motor. located within the accessory section. Several of these systems have accessory devices. accessory drive gear Besides being the main link between the starting system drive components and the gas turbine. located on the bottom of the base. starting motor. Four lifting trunnions and supports are provided. Many systems are involved in the operation of the turbine. one near each corner of the base. The interior of the base forms a self-contained. fabricated of steel I-beams and plate. A pressure gauge and switch cabinet located on the left side of the accessory compartment (looking downstream). torque converter. Lubrication system. starting equipment and various accessory equipment devices besides forming the lube storage tank (reservoir). one near each end of the base. the accessory drive gear is the gear reduction unit connected directly to the turbine for driving several of the accessory devices of the gas turbine support systems. or mechanisms. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . The bottom plate of the lube reservoir is positioned at a slight angle that slopes toward two drain pipes and plugs. Turning gear motor.48 10. 10. Liquid fuel system. namely. facilitate its mounting on the site foundation. for lifting the accessory compartment. Fabricated supports and mounting pads are welded to the upper surface of the base for mounting the accessory gear. GENERAL AND ACCESSORY BASE Most of the mechanical and electrical auxiliary equipment necessary for starting and operating the gas turbine is contained within the accessory compartment.1A CCESSORY B ASE The base of the accessory compartment is a structural steel assembly. lube storage reservoir located between the top and bottom plates of the steel beam framework. and other accessory components. A bolted access cover plate is provided at the control compartment end for access to the lube reservoir. It forms a mounting or support platform for the accessory gear. This enclosure and its components are mounted on a separate structural base located forward of the gas turbine compartment. fuel oil pump. contains panel mounted gauges and switches used with the systems mentioned above. On-base portion of the turbine cooling water system Several major components mounted on the accessory base include. Hydraulic system. Finished pads or sole plates. 11. after which there is another expansion joint. Two silencers are installed in series in the duct (the first one for the low frequency noises. before exhaust either to atmosphere. Prepared by: Fazal-ur-Rehman Babar GT 5-8 . followed by sections of parallel baffles silencers. At the exhaust end of the gas turbine. the gases which have been used to power the turbine wheels are redirected to be either released to atmosphere. The silencers are of baffle-type construction to attenuate the high frequency noise in the air inlet. the hot gases reach the diffuser. From these thermocouples turbine spread is measured. The exhaust plenum configuration is that of a box open on a side and welded to an extension of the turbine base. 11. gases produced as the result of combustion in the turbine require specific equipment according to their exhaust to atmosphere or towards heat recovery boilers. The thermocouples send their signals to the gas turbine temperature control and protection system. caused by the rotating compressor blading.1 A IR I NLET S YSTEM The air inlet system is at down-stream of the air filtering installation. On the exhaust plenum wall facing the exhaust diffuser there are 24 thermocouples arranged in circular measure exhaust gas temperature.49 11. A flow path from the exhaust plenum open side to a duct is provided by an extension plenum and an expansion joint. The gas turbine inlet plenum contains the compressor inlet casing. located in the exhaust plenum. Insulation in the plenum fabrication provides thermal and acoustical protection. or towards a heat recovery boiler. upwards or to a recovery boiler. It consists of an air duct.2 E XHAUST G AS S YSTEM In the exhaust section. then a screen system located in an inlet elbow. INLET AND EXHAUST SECTIONS It is necessary to treat incoming atmospheric air before it enters the turbine in order to adapt to the environment and realize the desired machine performance. It is necessary also to attenuate the high frequency noise in the air inlet. and an expansion joint after which air will reach the gas turbine air inlet plenum. caused by the rotating compressor blading. the second one for the high frequency noises). After leaving the exhaust frame. Specially designed equipment is installed to modify the quality of the incoming air to make it suitable for use in the unit. DUTY GAS TURBINE GT 5-8 COMPRESSOR 1 Inlet plenum assembly 2 Inlet casing 3 Magnetic pickup arrangement 4 Thrust bearing 5 No 1 bearing 6 Variable inlet guide vane arrangement 7 Compressor blading 8 Compressor rotor assembly 9 Forward compressor casing 10 After compressor casing 11 Compressor discharge casing 12 Inner compressor discharge casing 13 Turbine forward support 14 Turbine base COMBUSTION 15 Combustion wrapper 16 Fuel nozzle assembly 17 Combustion liner 18 Transition piece 19 Combustion chamber arrangement 20 Spark plug 21 Flame detector TURBINE 22 Turbine casing & shrouds 23 First stage nozzle 24 Second stage nozzle & diaphragm 25 Turbine stage nozzle & diaphragm 26 Turbine rotor assembly - Forward shaft First stage turbine wheel & bucket assembly Second stage turbine wheel & bucket assembly Third stage turbine wheel & bucket assembly Spacer wheels After shaft 27 No 2 bearing 28 No 3 bearing 29 Turbine after supports AIR INLET 50 COMPRESSOR COMBUSTOR TURBINE EXHAUST EXHAUST 30 Exhaust hood 31 Exhaust diffuser 32 Load coupling 33 Turbine vanes 34 Control & regulation thermocouples 35 Exhaust plenum assembly .50 GAS TURBINE MODEL FRAME 9001 E SIMPLE .SHAFT. SINGLE . HEAVY .CYCLE. 51 AIR INLET 51 COMPRESSOR COMBUSTOR TURBINE EXHAUST .