RAW MATERIALS USED AND THEIR SUPPLIERS

BHARAT HEAVY ELECTRICALS LIMITED

BHOPAL

SUMMER INDUSTRIAL TRAINING

Department: STEAM TURBINE MANUFACTURING (STM)

Under The Guidance Of :

Shri. D.D. Pathak, AGM,STMFrom: 16th May to 11th June 2011Submitted By:

Mohit AssudaniMaulana Azad National Institute Of Technology (MANIT) Bhopal

Mechanical Engineering

Scholar No: 081116052STEAM TURBINE:Asteam turbineis a mechanical device that extractsthermal energyfrom pressurizedsteam, and converts it into rotary motion. Its modern manifestation was invented bySir Charles Parsonsin 1884. It has almost completely replaced thereciprocatingpistonsteam engine(invented byThomas Newcomenand greatly improved byJames Watt) primarily because of its greater thermal efficiency and higherpower-to-weight ratio. Because the turbine generatesrotary 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 ofheat enginethat derives much of its improvement inthermodynamic efficiencythrough the use of multiple stages in the expansion of the steam, which results in a closer approach to the idealreversible process.History

The first device that may be classified as a reaction steam turbine was little more than a toy, the classicAeolipile, described in the 1st century byHero of AlexandriainRoman Egypt.A thousand years later, the first impact steam turbine with practical applications was invented in 1551 byTaqi al-DininOttoman Egypt, who described it as a prime mover for rotating aspit. Similarsmoke jackswere later described byJohn Wilkinsin 1648 andSamuel Pepysin 1660. Another steam turbine device was created by ItalianGiovanni Brancain 1629.

The modern steam turbine was invented in 1884 by the EnglishmanSir Charles Parsons, whose first model was connected to adynamothat 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,George Westinghouse. A number of other variations of turbines have been developed that work effectively with steam. Thede Laval turbine(invented byGustaf de Laval) accelerated the steam to full speed before running it against a turbine blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, considerably less efficient. The Parson's turbine also turned out to be relatively easy to scale-up.Parsonshad the 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 50,000 kW capacity. He knew that the total output from turbo-generators constructed by his firmC._A._Parsons_and_Companyand by their 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 ConditionsThese types include condensing, noncondensing, reheat, extraction and induction.

Noncondensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, anddesalinationfacilities where large amounts of low pressure process steam are available.

Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of aqualitynear 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 into an intermediate pressure section of the turbine and continues its expansion.

Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boilerfeedwater heatersto improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled.

Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

Casing or Shaft ArrangementsThese arrangements include single casing, tandem compound and 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 number of stages. These stages are characterized by how the energy is extracted from them and are known asimpulseorreactionturbines. 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 TurbinesAnimpulse turbinehas fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor 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 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 TurbinesIn thereaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction 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 pressure drop occurs across both the stator and the rotor, with steam 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 Turbine is a tandem compound machine with separate HP,OP 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 control valve combinations.Cross around pipes connect IP and LP cylinders.Connections are provided at several points of the turbine for feedwater extraction purposes.HP TURBINE, BARREL TYPE CASINGThe 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 high thermal stresses.The Inner Casing is axially split and supported so as to be free to move in response of thermal expansion.The Barrel Type casing permits flexibility of operation in the form of short startup times and a high rate of change of load even at initial steam conditions.

IP TURBINEThe IP turbine section is of singleconstruction with horizontal split casings.The inner casing carries the stationary blading.The Reheated steam enters the inner casing from top and bottom.The provision of an Inner Casing confines 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 expansion within the intermediate shell.Guide blade carriers,carrying 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. The IP and LP rotors have a journal b earing each at rear end.The combined journal and thrust bearing incorporates a journal and a thrust bearing which takes up residual thrust from both directions.The Bearing pedestals are anchored to the foundation by means of anchor bolts and are fixed by position,The HP and IP turbines rest with their lateral support horns on the bearing pedestals at the turbine centerline level.

The Axial position of HP and IP casings is fixed at the support brackets on HP-IP bearing pedestals.

The Following components forms the fixed points for the turbine:

1.The HP,IP and LP turbine bearing pedestals

2.The horn supports of the HP and IP turbine at HP-IP Pedestals

3.At the middle of longitudinal girder of the LP Turbine

4.The Thrust Bearing in the HP turbine rear bearing pedestals

CASING EXPANSIONCentring 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 there is 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.

Differential expansion between rotor and casing of the IP turbine results from the difference between the expansion of the shaft assembly, originating from thrust bearing and casing expansion ,which originates from the fixed points on the LP turbine longitudinal beams.SHAFT SEAL and BLADE TIP SEALING

All shaft seals,which seal the steam in the casing against atmosphere,are axial-flow type.They 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 main stop valves are spring action single seated valves,the control valves,also of single seat design ;the control valves;also of single-seat design,have diffusers to reduce pressure losses.

The Ip turbine has 2 reheat stop and control valves.The reheat stop valves are spring action single stop valves.The control valves;also spring loaded ,have diffusers.

The reheat stop and control valves are supported free to move in response tto thermal 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.The linear power frequency droopcharacteristic can be adjusted in fine steps even when the turbine is running

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 SYSTEMA common oil supply system lubricates and cools 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 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:IntroductionA steam turbine is a 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 pistons. This has now been almost totally replaced by the steam turbine 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 used in power stations. The steam turbine derives much of its better thermodynamic efficiency because of the use of multiple stages in the expansion of the steam. This results in a closer approach to the ideal reversible process.Steam turbines are made in a variety of sizes ranging from small 0.75 kW units used as mechanical drives for pumps, compressors and other shaft driven equipment, to 1,500,000kW turbines used to generate electricity.Steam turbines are widely used for marine applications for vessel propulsion systems.In recent times gas turbines , as developed for aerospace applications, are being used more and more in the field of power generation once dominated by steam turbines.

Steam Turbine PrincipleThe steam energy is converted mechanical work by expansion through the turbine. Th expansion takes place through a series of fixed blades (nozzles) and moving blades each row of fixed blades and moving blades is called a stage. The moving blades rotate on the central turbine rotor and the fixed blades are concentrically arranged within the circular turbine casing which is substantially designed to withstand the steam pressure.On large output turbines the duty too large for one turbine and a number of turbine casing/rotor units are combined to achieve the duty.These are generally arranged on a common centre line (tandem mounted) but parallel systems can be used called cross compound systems.

Impulse BladingThe 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.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

Velocity diagram impulse turbine stagez represents the blade speed , Vrrepresents the relative velocity, Vwa& Vwb- represents the tangential component of the absolute steam in and steam out velocitiesThe power developed per stage = Tangential force on blade x blade Reaction BladingThe reaction blading principle depends on the blade diverting the steam flow and gaining kinetic energy by the reaction. The Catherine wheel (firework) is an example of this principle.FOr this turbine principle the steam pressure drop is divide between the fixed and moving blades.

Velocity diagram reaction turbine stagez represents the blade speed , Vrrepresents the relative velocity, Vwa& Vwb- represents the tangential component of the absolute steam in and steam out velocitiesThe power developed per stage = Tangential force on blade x blade speed.

Power /stage= (Vw a - Vwb).z/1000 kW per kg/s of steam

The blade speed z is limited by the mechanical design and material constraints of the blades.Rankine Cycle

The Rankine cycle is a steam cycle for a steam plant operating under the best theoretical conditions for most efficient operation.This is an ideal imaginary cycle against which all other real steam working cycles can be compared.The theoretic cycle can be considered with 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 water). The feed pump will add no energy to the water. The chimney gases would be at the same pressure 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 expansion (h2) this being isentropic (reversible 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).

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

Although the theoretical best efficiency for any cycle is the Carnot Cycle the Rankine cycle provides a more practical ideal cycle for the comparision of steam power cycles ( and similar cycles ). The efficiencies of working steam plant are determined by use of the Rankine cycle by use of the relative efficiency or efficiency ratio as below:The various energy streams flowing in a simple steam turbine system as indicated in the diagram below. It is clear that the working fluid is in a closed circuit apart from the free surface of the hot well.Every time the working fluid flows at a uniform rate around the circuit it experiences a series of processes making up a thermodynamic cycle.The complete plant is enclosed in an outer boundary and the working 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 streams and crossing the boundaries.This allows energy equations to be developed for the individual units and the whole plant...When the turbine system is operating under steady state conditions the law of conservation of energy dictates that the energy per unit mass of working agent ** entering any system boundary must be equal to the rate of energy leaving the system boundary.**It is acceptable to consider rates per unit mass or unit time whichever is most convenient

Steady Flow Energy Equations

Boiler

The energy streams entering and leaving the boiler unit are as follows:

F + A + hd= h1+ G + hlb hence F + A = G + h1- hd+ hlbTurbine

The energy streams entering and leaving the boiler unit are as follows:

h1= T + h2+ hlthence0 = T - h1+ h2+ hltCondenser Unit

The energy streams entering and leaving the boiler unit are as follows:

Wi+ h2= Wo+ hw+ hlc hence Wi= Wo+ hw- h2+ hlc

Feed Water System

The energy streams entering and leaving the Feed Water System are as follows:

hw+ de+ df= hd+ hlfhencede+ df= - hw+ hd+ 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 - (de+ df)- the energy leaving the exhaust [G - A] using the air temperature as the datum.-the energy gained by the water circulating through the condenser [Wo- Wi]- the energy gained by the atmosphere surrounding the planthl

The overall thermal efficiency of a steam turbine plant can be represented by the ratio of the net mechanical energy available to the energy within the fuel supplied. as indicated in the expressions below...

Turbine Vapour Cycle on T-h DiagramSteam cycle on Temp - Enthalpy DiagramThis cycle shows the stages of operation in a turbine plant. The enthalpy reduction in the turbine is represented by A -> B . The reversible process for an ideal isentropic (reversible adiabetic) is represented by A->B'. This enthalpy loss would be (hg1- h2) in the reversible case this would be (hg1- h2s).The heat loss by heat transfer in the condenser is shown as B->C and results in a loss of enthalpy of (h2- hf2) or in the idealised reversible process it is shown by B'-> C with a loss of enthalpy of (h2s- hf2).The work done on the water in extracting it from the condenser and feeding it to the boiler during adiabetic compression C-> D is (hd- hf2) = length MThe energy added to the working agent by heat transfer across the heat transfer surfaces in the boiler is (hg1- hd) which is approx.( hg1- hf2)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)

Horizontal Boring Machine:

No. 20/A/2111

Spindle diameter: 127mm

Fending head:1524 mm

Width of table =1524 mm

Maximum dia of boring bar = 158.80 mm

Feeds=129- 38 mm

Morando Boring Machine

No: 20/A/2012

Speed :1.5- 200 rpm

Feed: .5-2000 mm/minCentre Height: 770 mm

Distance between centres :6000 mm

On Swing Bed: 1520 mm

Max Weight on Centre= 30 Tons

Max Weight on face plate= 60 Tons

Richard Vertical Boring and Turning Machine

No : 20/A/11

Speed : .48- 13 rpm

Feed: .501 102.51 mm/min

Dia: 4877 mm

Max Turning Diameter: 4955 mm