BHEL Bhopal STM Training Report

BHARAT HEAVY ELECTRICALS LIMITED

BHOPAL SUMMER INDUSTRIAL TRAINING Department: STEAM TURBINE MANUFACTURING (STM)

Under The Guidance Of : Shri. D.D. Pathak, AGM,STM From: 16th May to 11th June 2011

Submitted By: Mohit Assudani Maulana Azad National Institute Of Technology (MANIT) Bhopal Mechanical Engineering Scholar No: 081116052

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STEAM TURBINE: A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884. It has almost completely replaced the reciprocating piston steam engine (in (inven vented ted by Thom Thomas as Newc Newcom omen en and greatly improved by James Watt) Watt) primarily because of its greater thermal efficiency and higher powe higher power-tor-to-weigh weightt ratio. ratio. Beca Becaus use e the the turb turbin ine e gene genera rate tes s rotary motion, motion, it is particularly suited to be used to drive an electrical generator – about 80% of all electricity generation in the world is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its its impr improv ovem emen entt in thermodynamic thermodynamic efficiency thro throug ugh h the the use use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible process. process .

History The first device that may be classified as a reaction steam turbine was little more than than a toy, toy, the the clas classi sic c Aeolipile Aeolipile, desc descri ribe bed d in the the 1st 1st cent centur ury y by Hero Hero of Alexandria Alexandria in Roman Roman Egypt Egypt.. A thou thousa sand nd year years s late later, r, the the firs firstt impa impact ct stea steam m turbine with practical applications was invented in 1551 by Taqi al-Din in i n Ottoman Egypt, Egypt , who described it as a prime mover for rotating a spit. spit. Similar smoke Similar smoke jacks were later described by John Wilkins in 1648 and Samuel Pepys in 1660. Another steam turbine turbine device device was created by by Italian Giovanni Branca in 1629. The modern steam turbine was invented in 1884 by the Englishman Sir Charles Parsons, Parsons , whose first model was connected to a dynamo that generated 7.5 kW of electricity. Parson's steam turbine, making cheap and plentiful electricity possible and revolutionising marine transport and naval warfare, the world would never be the same again.. His patent was licensed and the turbine scaled-up shortly after by an American, American, George Westinghouse. Westinghouse . A number of other variations of turbines have have been been deve develo lop ped that that work work effe effect ctiv ivel ely y with ith stea steam. m. The The de Lav Laval









satisfaction of seeing his invention adopted for all major world power stations. The size of his generators had increased from his first 7.5 kW set up to units of 50,00 50,000 0 kW capac capacity ity.. He knew knew that that the total total output output from from turbo turbo-ge -gene nerat rators ors constructed constructed by his firm C._A._Parsons_and_Company and by their licensees, licensees, for land purposes alone, had exceeded thirty million horse-power.. Within Parson's lifetime the generating capacity of a unit was scaled-up by about 10,000 times.

Types Steam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines .

Steam Supply and Exhaust Conditions These These types types includ include e conden condensi sing, ng, nonco noncond ndens ensing ing,, rehea reheat, t, extra extracti ction on and and induction. Noncond Noncond

ing

backpre backpre

turbines turbines

most widely

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Condensing Condensing turbines are most commonly found in electrical electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser. Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back back into into an inter intermed mediat iate e press pressur ure e sectio section n of the the turbi turbine ne and conti continue nues s its expansion. Extracting type turbines are common in all applications. In an extracting type turbin turbine, e, steam steam is relea released sed from from vario various us stag stages es of the turbi turbine, ne, and and used used for industrial process needs or sent to boiler feedwater heaters to improve overall cycl cycle e effi effici cien ency cy.. Extr Extrac acti tion on flow flows s may may be cont contro roll lled ed with with a valv valve, e, or left left uncontrolled. Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

Casing or Shaft Arrangements These These arra arrange ngeme ments nts includ include e singl single e casin casing, g, tande tandem m compo compoun und d and and cross cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.









Turbine Efficiency

Schematic diagram outlining the difference between an impulse and a reaction turbine

To maximize turbine efficiency, the steam is expanded, generating work, in a numbe numberr of stages stages.. These These stages stages are chara charact cteri erize zed d by how how the the energ energy y is extr extrac acte ted d from from them them and are are know known n as impulse or reaction turbines turbines.. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.









Impulse Turbines An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain contain significant kinetic kinetic energy, which the rotor blades, blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage. As the steam flows through the nozzle its pressure pressure falls from steam chest pressure to condenser pressure (or atmosphere pressure). Due to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss".

Reaction Turbines In the react reaction ion turbin turbine, e, the the rotor rotor blad blades es thems themselv elves es are arra arrange nged d to form form conver convergen gentt nozz nozzles les.. This This type type of turbin turbine e makes makes use use of the the react reactio ion n force force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pres pressu sure re drop drop occu occurs rs acro across ss both both the the stat stator or and and the the roto rotor, r, with with stea steam m accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.











Steam Turbine: DESCRIPTION: Construction, STEAM FLOW The The Turb Turbine ine is a tandem tandem compo compoun und d machin machine e with with sepa separat rate e HP,O HP,OP P and and LP sections.The HP section being a single flow cylinder abd IP and LP sections double flow cylinders.The Turbine Rotors and the generator rotors are connected by rigid couplings. The HP turbine is throttle controlled.The Initial steam is admitted ahead of the blading via 2 main stop and control valve combinations.A swing check valve is installed in the line leading from HP turbine exhaust to the reheater to prevent hot steam from reheater flowing back into HP turbine. The Steam coming from reheater is passed to the IP turbine via 2 reheat stop and and cont contro roll valv valve e comb combin inat atio ions ns.C .Cro ross ss arou around nd pipe pipes s conn connec ectt IP and and LP cylinders.Connec cylinders.Connections tions are provided provided at several points of the turbine for feedwater feedwater extraction purposes.

HP TURBINE, BARREL TYPE CASING The outer casing of the HP turbine is of the barrel type and has neither an axial nor radial flange.This prevents mass concentration which would have caused









IP TURBINE

The IP turbine section is of singleconstruction with horizontal split casings.The inner casing carries the stationary blading.The Reheated steam enters the inner casing casing from top and bottom.The bottom.The provision provision of an Inner Inner Casing Casing confine confines s high steam inlet conditions to the admission section of this casing.

LP TURBINE

The Casing of double-flow LP cylinder is of three shell design.The shells are horizontally split and are of rigid welded construction.The innermost shell,which carries the first rows of stationary blades ,is supported so as to allow thermal expan expansio sion n withi within n the the interm intermed ediat iate e shell shell.G .Guid uide e blad blade e carri carrier ers,c s,carr arryin ying g the stationary blade rows are also attached to the intermediate shell .

BEARINGS The HP rotor is supported on two bearings,a journal bearing at its front end,and a combined journal and thrust bearing immediately next to the coupling to the IP rotor. rotor. The IP and and LP rotors rotors have a journ journal al b earin earing g each each at rear rear end.T end.The he combined journal and thrust bearing incorporates a journal and a thrust bearing which takes up residual thrust from both directions.









3.At the middle of longitudinal girder of the LP Turbine 4.The Thrust Bearing in the HP turbine rear bearing pedestals

CASING EXPANSION Centring of LP outer casing is provided by guides which run in recesses in the foundation cross beam. Axial movement of casings is unrestrained. Hence,when Hence,when there is temperature temperature rise,the outer casing of the HP turbine expand from their from their fixed points towards front pedestals.Casing of IP Turbine expand from its fixed point towards the generator. LP Casing expands from its fixed point at front end ,towards the generator.

Rotor Expansion The Hp turbine rotor expands from the thrust bearing towards the front bearing pedestal of the HP turbine and the Ip turbine Rotor from the thrust bearing towards the generator. The LP turbine rotor is displaced towards the generatorby the expansion of the shaft assembly ,originating from the thrust bearing.

DIFFERENTIAL EXPANSION Differential expansion between rotors and casings results from the difference between the expansion of rotor and casing originating from the HP-IP pedestal.









SHAFT SEAL and BLADE TIP SEALING All shaft seals,which seals,which seal the steam in the casing against atmosphere,are atmosphere,are axialflow type.They consists consists of a large number of thin seal strips which,in the HP and Ip turbines are caulked alternately into grooves in the shafts and the surrounding seal rings.

VALVES The HP turbine is fitted with2 main stop and control valves.The valves.The main stop valves are spring spring action action single single seated seated valves,t valves,the he control control valves,also valves,also of single single seat design design ;the control control valves;a valves;also lso of single-s single-seat eat design, design,have have diffuse diffusers rs to reduce reduce pressure losses. The Ip turbine has 2 reheat stop and control valves.The reheat stop valves are spring spring action action single single stop valves.T valves.The he control control valves; valves;also also spring spring loaded loaded ,have ,have diffusers. The reheat stop and control control valves are are supported supported free to move in response response tto thermal expansion expansion on the foundation cover plate below the operating floor and in front of the turbine generator unit.

TURBINE CONTROL SYSTEM The Turbine has an electrohydraulic control system.An electric system measures spped and output and controls them by controlling the control valve hydraulically via an electrohydraulic converter.









TURBINE MONITORING SYSTEM In addition to measuring and display instruments for pressure,temperatures,valve lifts and speed ,the monitoring system also includes following parameters : 1.Rotor expansion measured at the rear bearing pedestal of LP turbine. 2.Axial Shift measured at the HP-IP pedestal 3.Bearing pedestal vibration 4.Shaft vibration measured at all turbine bearings.

OIL SUPPLY SYSTEM A common oil supply system lubricates lubricates and cools the bearings.The bearings.The main oil pump is driven by the turbine shaft and draws oil from the main oil tank.Auxiliary oil pumps maintain the oil supply on start-up and shutdown, during turning gear operation and when the main oil supply is faulted. A jack oil pump forces high pressure pressure oil under the shaft journals to prevent boundary lubrication during turning gear operation.The Lubricating and cooling oil is passed through oil coolers before entering the bearings.











Working Of A STEAM TURBINE: Introduction A steam turbine is a mechanical mechanical device that converts thermal energy in pressurised steam into useful mechanical work. The original steam engine which largely powered the industrial revolution in the UK was based on reciprocating pisto pistons. ns. This This has has now now been been almost almost total totally ly repla replaced ced by the steam steam turbin turbine e because the steam turbine has a higher thermodynamic efficiency and a lower power-to-weight ratio and the steam turbine is ideal for the very large power configurations configurations used used in power stations. stations. The steam steam turbine derives derives much of its better thermodynamic efficiency because of the use of multiple stages in the expansion expansion of the steam. steam. This results results in a closer approach approach to to the ideal reversible reversible process. Steam turbines are made in a variety of sizes ranging from small 0.75 kW units used used as mechan mechanic ical al drive drives s for for pumps pumps,, compr compress essors ors and and other other shaft shaft drive driven n equipment, to 1,500,000kW turbines used used to generate electricity. Steam turbines are widely used for marine applications applications for vessel vessel propulsion systems. systems. In recent times gas turbines , as developed for aerospace applications, are being used more more and and more more in the field of power power gener generat ation ion once once domin dominat ated ed by steam steam turbines.









arranged on a common centre line (tandem mounted) but parallel systems can be used called cross compound systems.

Impulse Blading The impulse blading principle is that the steam is directed at the blades and the impact of the steam on the blades drives them round. The day to day example of this principle is the pelton wheel.ref Turbines. Turbines . In this type of turbine the whole of the stage pressure drop takes place in the fixed blade (nozzle) and the steam jet acts on the moving blade by impinging on the blades.

Blades of an impulse turbine









Reaction Blading The reaction blading principle depends on the blade diverting the steam flow and gaining gaining kinetic kinetic energy energy by the reaction. reaction. The Catherin Catherine e wheel (firewor (firework) k) is an example of this principle. principle. FOr this turbine principle principle the steam pressure drop is divide between the fixed and moving blades.

Velocity diagram reaction turbine stage









Rankine Cycle The Rankine cycle is a steam cycle for a steam plant operating under the best theoreti theoretical cal conditi conditions ons for most most efficien efficientt operati operation. on. This is an ideal ideal imagina imaginary ry cycle cycle agai against nst which which all other other real real steam steam work working ing cycle cycles s can can be compa compare red. d. The theoretic cycle can be considered considered with reference reference to the figure below. There will no losses of energy by radiation, leakage of steam, or frictional losses in the mechanical componets. The condenser cooling will condense the steam to water with only sensible heat (saturated (saturated water). water). The feed pump will will add no energy to the the wate water. r. The The chim chimne ney y gase gases s woul would d be at the the same same pres pressu sure re as the atmosphere. Within the turbine the work done would be equal to the energy entering the turbine as steam (h1) minus the energy leaving the turbine as steam after perfect expansio expansion n (h2) this being isentrop isentropic ic (reversib (reversible le adiabatic adiabatic)) i.e. (h1- h2). The energy supplied by the steam by heat transfer from the combustion and flue gases in the furnace to the water and steam in the boiler will be the difference in the enthalpy of the steam leaving the boiler and the water entering the boiler = (h1 - h3).









The ratio output work / Input by heat transfer is the thermal efficiency of the Rankine cycle and is expressed as

Although the theoretical theoretical best efficiency efficiency for any cycle is the Carnot Cycle the Rankine cycle provides a more practical ideal cycle for the comparision of steam power cycles cycles ( and similar similar cycles ). The efficiencies efficiencies of working working steam steam plant are determined by use of the Rankine cycle by use of the relative efficiency or efficiency ratio as below: The The variou various s energ energy y stream streams s flowin flowing g in a simple simple steam steam turbi turbine ne syste system m as indicated in in the diagram diagram below. below. It is clear that that the working working fluid is in a closed closed circuit circuit apart from the free free surface surface of the hot well. Every Every time the working working fluid fluid flows at a uniform rate around the circuit it experiences a series of processes making up a thermodynamic cycle. The The comple complete te plant plant is enclo enclosed sed in an oute outerr boun bounda dary ry and the the worki working ng fluid fluid crosses inner boundaries (control surfaces).. The inner boundaries defines a flow process. The various identifiers represent the various energy flows per unit mass flowing along the steady-flow steady-flow streams and crossing crossing the boundaries. This allows energy energy



















Feed Water System

The energy streams entering and leaving the Feed Water System are as follows: h w + d e + d f = h d + hl f hence d e + d f = - h w + h d + hl

The four equations on the right can be arranged to give the energy equation for the whole turbine system enclosed by the outer boundary That is ..per unit mass the of working agent (water) the energy of the fuel (F) is equal to the sum of - the mechanical energy available from the turbine less that used to drive the pumps (T - (d e+ d f )









The work done on the water in extracting it from the condenser and feeding it to the boiler during adiabetic compression C-> D is (h d - h f2 ) = length M The energy added to the working agent by heat transfer across the heat transfer surfaces in the boiler is (h g1 - h d ) which is approx.( h g1 - h f2 ) The Rankine efficiency of the Rankine Cycle AB'CDEA is

The efficiency of the Real Cycle is









Following were Some of the machines used for the manufacturing of the steam turbine parts Craven Lathe machine

No .20/A/30 Speed : .5-51 rpm Distance from the centre : 7620 mm Maximum swing over 1676 mm Head stock Face Plate diameter : 1524 mm Face Plate gripping Capacity: 203-1270mm Load :90 tons (stades)

BHEL Bhopal STM Training Report

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