Presentation on theme: "PRESENTATION ON CONSTRUCTIONAL FEATURES OF 57.02MW STEAM TURBINE AT AES KELANITISSA BY G.SRIDHAR DEPUTY MANAGER/BHEL."— Presentation transcript:
PRESENTATION ON CONSTRUCTIONAL FEATURES OF 57.02MW STEAM TURBINE AT AES KELANITISSA BY G.SRIDHAR DEPUTY MANAGER/BHEL
STEAM TURBINE Single shaft non-reheat type reaction Turbine 1 st stage is an impulse stage Steam enters the turbine from the valves through the inter-connecting piping to the HP stages 17 HP stages After the doing work in the HP stages, the steam makes its way to the IP stages The IP stages are housed in Guide Blade Carriers(GBCs) 1, 2, 3 & 4
GBC-1 consists of 13 stages GBC-2 consists of 8 stages GBC-3 consists of 4 stages GBC-4 consists of 4 stages The last 4 stages are housed in the Exhaust Hood and are called the LP stages. A very important part of the rotor is the Balance Piston Disc/Drum which balances a major part of the thrust that is caused by impingement of steam on to the blades. The residual thrust is absorbed by the Thrust Bearing.
The HP and IP stages of the Turbine are separated by the Intermediate Gland The rotor is fixed at the thrust bearing and the expansion takes place towards the Generator. The casing is fixed at the Exhaust hood and expands towards the front bearing pedestal The front bearing housing rests on the bearing pedestal and slides on graphite studded packers along with the casing. The rotor rests on bearings in the front and rear bearing pedestals and resembles a simply supported beam.
In between the 2 bearing pedestals and the casings are the front and the rear glands. Gland steam for sealing the motive steam from coming out of the casing is supplied to these glands. The exhaust hood is provided with 2 nos. of explosion/bursting diaphragms which will operate when the exhaust hood pressure increases beyond a certain limit. The diaphragm is made of lead. On either side of the Turbine are the Main Steam Stop and Control Valves with servomotors. Steam from the Boiler enters the valves through a nozzle provided at the bottom of the valves. The valves house the strainer which prevents foreign particles from entering the Turbine.
From the valves, the steam is led to the Turbine through the Inter-connecting piping/Steam transfer piping. Looking from the Turbine towards the Generator, all that is in front, is front and that at the rear, the rear. Similarly the left and the right. The valves are fixed at the rear end in the axial direction and at one of the resting palms in the transverse direction thus enabling expansion of the valve towards the front and away from the Turbine laterally. The rear set of thrust pads are the active pads.
Mounted on the front bearing pedestal is the Main Oil Pump which is driven by the Turbine shaft. This pump comes into operation after the Turbine has attained 95% of rated speed. Till then the AOP shall be in operation. The front portion of the Turbine rotor is also equipped with a toothed wheel for sensing speed and a overspeed testing eccentric pin. The overspeed trip lever is lifted by the eccentric pin when the machine overspeeds, there by causing draining of oil and immediate closure of stop valves.
The Rear Bearing pedestal houses the rear bearing and the Turning/Barring Gear assembly. The coupling portion of the Turbine rotor is assembled with 1 stage of impulse blades on to which oil will impinge when the Turning Gear valve is opened. This will result in rotation of the rotor. For this the rotor has to be lifted on jacking oil by 0.07 to 0.10mm. Unlike the front bearing housing, the rear bearing housing does not slide. The rear bearing pedestal is also the house of the Turbine-Generator coupling.
The Steam Turbine is equipped with the following auxiliaries: a.Main Oil Tank b.Auxiliary Oil Pump-tank mounted c.Emergency Oil Pump-tank mounted d.Duplex Oil Filter e.Oil Coolers f.Oil Centrifuge g.AC & DC Jacking Oil Pumps h.CEPs, BFPs, Deaerator etc.
Sequence of Steam Turbine Erection 1.Mark the longitudinal and transverse center lines on the TG deck/verify the center lines marked by the civil agency. 2.The foundation shall be checked for dimensional accuracy by a measuring tape within a tolerance of +2mm. 3.Before the foundation is cast, check the location of inserts, pockets etc. The foundation bolt sleeves shall be checked for verticality and shall not deviate by more than 3mm along the entire height of the sleeve. The sleeves shall then be locked firmly to the reinforcement rods to arrest any movement during casting.
Care shall be taken to cast the entire deck in one stretch spanning 24 to 36 hours. The dimensional and verticality check shall be repeated after casting to check for any deviations during casting. After the minimum curing time of the deck has elapsed, its ready for erection. All dimensional checks shall be carried out with respect to the longitudinal axis of the Turbine and the Condenser center line. All areas where secondary grout is to be poured or where primary packers are to be grouted shall be roughly chipped. This is important for adhesion between the primary and the secondary grout.
A bench mark for reference elevation of the TG center line shall be transferred from the Boiler/any reference which the civil agency has marked. The elevation of all components of the Steam Turbine – Generator shall be set w.r.t this bench mark. Mark location of packers for placement of the Turbine Front and Rear pedestals, Exhaust hood base plate, the Generator sole plate and the Exciter sole plates. Place, align, set elevation and level the packers and grout with quick setting non-shrink cement. Cure the grout for as long as the manufacturer of the cement recommends. Packers shall be so placed to allow for provision of shims for adjustment.
48 hours after the packers have been grouted, they are ready for loading of the equipment. Place the Exhaust hood sole plates, the Turbine front and the Rear Bearing pedestals. All the above shall be aligned w.r.t the longitudinal and transverse axes of the Turbine. The elevations of the parting planes of the bearing pedestals shall be set w.r.t to the bench mark made earlier and shall correspond to the machine center line. Place the exhaust hood lower half on the sole plates. Bolt the lower half of the Outer Casing with the Exhaust hood lower half, while taking care to match the joint. The joint shall be checked on either side with a dial gauge. The outer casing bottom half rests on jack screws on the FBP.
A piano wire is then stretched from a temporary structure in front of the front bearing pedestal to a structure beyond the rear bearing pedestal at the same elevation as that of the machine centerline and shall hence forth be regarded as the longitudinal centerline of the machine. The seal bore of the pedestals and the front & rear portion of the casing shall be aligned w.r.t to the piano wire to an accuracy of 0.10mm. Place the top half of the outer casing and the exhaust hood and bolt the two together. This assembly cannot be made later as there is no space to tighten the bolts of the vertical joint. Remove the top half of the casing and place it on a level surface at a convenient location.
Level the rotor on the lifting beam and place the rotor on bearings. Clamp dial gauges to the rotor and achieve centering values of at the Turbine front and rear seal bore, at the front gland portion and the bellow location of the casing as has been recorded at works. Insert exhaust hood radial keys. Remove the rotor and place it back on the stands. Insert eccentric pin assemblies of the BP Gland, Inner casing and GBCs. Place the lower halves of BP Gland, Inner casing and all Guide Blade Carriers.
Set the gaps at the parting planes and the elevation of the parting planes of the BP Gland, Inner Casing and GBCs w.r.t the outer casing as given in the test bed protocols/shop quality records. Place the rotor now and check flow path clearances. The flow path clearances will be very nearly the same as recorded in the shop quality records. Check axial float of the rotor without the thrust bearing and record. Place the top halves of the BP Gland, Inner Casing and GBCs and check top clearances by lead wire or by float as is applicable.
Place the outer casing top half and carryout a mock box up. Lock the hexagonal screws of the eccentric pins in this position. Remove the top halves of all the assemblies and the rotor. Assemble the rotor simulation thermoelement and the 1 st stage pressure piping on the Inner Casing. Remove the bottom halves of the BP Gland, Inner Casing and all GBCs. Fix a date for final box-up and carryout complete cleaning of the bottom half of the casing.
Place the bottom halves of the BP Gland, Inner Casing and all GBCs. The rotor shall now be lifted with the axial compensator(bellow) assembled and placed in position. Restricted entry to the area may be allowed and it may be ensured that all personnel working on the Turbine have emptied pockets. Once the rotor is placed in position, the box-up shall be completed with no interruptions at least until the top halves of the BP Gland, Inner Casing and all GBCs are placed.
Place the top halves of the BP Gland, Inner Casing and all GBCs. Apply Steam Jointing Paste at the parting plane. The usually recommended pastes are BIRKOSIT or STAG-B Heat tighten the Inner casing parting plane bolts. Tighten all other parting plane bolts as mentioned in the bolt tightening protocol. It is important to follow the sequence of tightening as given in the drawing. Remove all vertical dowel pins from the BP Gland, Inner Casing and all GBCs. Tack weld those nuts which have not been heat tightened.
Place the outer casing top half and tighten the parting plane bolts. This completes box-up. Until this point, the entire weight of the front portion of the casing had been transferred to the front bearing pedestal vide jacking screws. Now, transfer the load of the casing from the jack screws to the load bearing screw and pad assembly in the FBP. Release the jack screw. Recheck centering of the Turbine casing w.r.t after transferring of load and in case of change, re-center the casing to the original values. Fill a sand-cement mixture into the foundation bolt sleeves, carryout shuttering and grout the Front Bearing pedestal, the Exhaust hood sole plate and the Rear Bearing Pedestal with quick setting cement.
48 hrs after grouting, tighten all foundation bolts of the Turbine FBP, EH and RBP to required values mentioned in the drawing. Align Generator rotor with the Turbine rotor. A misalignment of +0.02mm radially and axially is permissible. Record free runouts of the Turbine and Generator rotors at the journals and the coupling. Couple the Turbine and Generator rotors using the 4 auxiliary coupling bolts supplied and achieve runouts, the same or with minor variation of free runout. Ream and Hone the coupling bolt holes and machine the bolts so as to have a clearance of 0.02mm between the bolt and the hole. Stretch the coupling bolts to the required value and record coupled runout again.
While Reaming and Honning of the Turbine-Generator coupling is in progress, Inter-connecting pipes between valves and Turbine can be installed. The Main Steam Inlet Insert is inserted through the outer casing into an opening in the inner casing. The insert is kept in position by ring nuts which are threaded on to the outer casing. Leakage of steam from the inner casing to the outer casing is sealed by the U-sealing ring. The inter-connecting pipes are supported by dampers and supports extending from the valve block. After welding and stress relieving of the inter-connecting pipes is completed, the centering of the casing w.r.t the rotor shall be checked.
TURBOGENERATOR The Turbogenerator supplied for this project is of Air cooled type. 5 coolers have been supplied, of which 1 shall be spare. The Generator Stator rests on sole plates which are welded at site to form an assembly. The Generator rotor rests on 2 bearings, much like the Turbine rotor. The air gap of the Generator is adjusted by shims provided underneath the bearing pedestals. The air gap is set and the bearing pedestals are dowelled.
For alignment of the Generator rotor with the Turbine rotor, the Turbine rotor is assumed to be the reference rotor. The entire Turbogenerator assembly is moved left/right and top/bottom to achieve the desired alignment. While carrying out the radial and axial alignment, care shall be taken to fix the axial position of the stator by measuring the axial clearances at various locations. The Generator rotor has 2 sets of fan blades, one each on the front and rear sides. These fan suck air and discharge them into the stator for cooling of the windings.
The radial and axial clearances of the fan blades rings and the end shields shall be maintained as per drawing. After alignment of Turbine-Generator rotors, alignment of Exciter rotor with Generator rotor shall be done. The Exciter rotor shall be axially aligned and swing check carried out. The swing check values for this Exciter shall be = 0.05mm. After the alignment and swing check of Exciter the axial and radial clearances of the Main Exciter and the PMG shall be maintained as per drawing. In this condition, the Generator and the Exciter can be boxed-up. The rotor, all along until now required rotation for alignment, coupling, swing check, etc. Since rotation of the rotor will not be required any longer, the “ZERO” position of the rotor can be set and released for Turbovisory work.
The “Zero” position of the rotor is that position of rotor about which, the float on either side of the thrust bearing is equal i.e; the rotor has been set at mid float. It is this position of the rotor w.r.t which the Differential expansion probe and the axial shift probe are set. While Turbovisory works are on, thermal clearances on holding down bolts at various locations are to be made as per drawings. On completion of Turbovisory works in the pedestals, the bearing pedestals can be boxed-up. The machine is now ready for Turning Gear operation. Set rotor lift of 0.07 to 0.10mm by adjusting jacking oil pressure in each bearing and put the machine on Turning Gear. The machine is now set to receive steam.