alstom

Steam Turbines Introduction Brajbhushan MISHRA Steam Turbine Engineering & KWU Business Development

15/05/2008

POWER SERVICE

STEAM TURBINES

Introduction to Steam Turbines

Steam Ste am Turbine Turbiness Introdu Introducti ction on - 31/ 31/07/ 07/200 2008 8-P2 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Energy Conversion Cycle

IGNITION OF COAL/ OIL

CV OF FUEL CONVERTED INTO HEAT ENERGY

BOILER

HEATING OF WATER

HEAT ENERGY CONVERTED INTO STEAM PRESSURE

HEAT EXCHANGER

STEAM PRESSURE CONVERTED

MECH. WORK TO ELECTRIC POWER

INTO MECHANICAL WORK

GENERATOR

Steam Ste am Turbine Turbiness Introdu Introducti ction on - 31/ 31/07/ 07/200 2008 8-P3 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

TURBINE

STEAM TURBINES - Introduction

The Steam Turbine is a Prime-mover in which the Potential Energy (in the form of Heat and Pressure) is transformed into Kinetic Energy and the latter in its turn is transformed into the Mechanical Energy of rotation of turbine shaft.

Steam Turbines Introduction - 31/07/2008 - P 4 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Fundamental Laws INTRODUCTION: The Steam Turbine is governed by following laws: • The law of Conservation of Mass • The law of Conservation of Energy • The law of Conservation of Momentum • Euler’s Turbine Equation


STEAM TURBINES - Earlier “Turbines”

Impulse Turbine built by Giovanni Branca in A.D.1629

Reaction turbine Turbine built by Hero of Alexandria in B.C. 120


STEAM TURBINES - Typical Steam Cycle


STEAM TURBINES - Typical TG arrangement


STEAM TURBINES

Classification of Steam Turbines


STEAM TURBINES - Classification

•

Based on ACTION of steam:

Impulse, Reaction, Combined

•

Based on FLOW DIRECTION of steam :

Axial, Radial, Mixed flows Single flow & Double flow

•

Based on FINAL STATE of steam:

Condensing, Back Pressure

•

Based on CYCLE followed by steam:

Reheat, Regenerative

•

Based on No. of STAGES :

Single stage, Multi stage

•

Based on No. of CYLINDERS/ CASING :


Single & Multi Cylinder Single & Double (inner & outer) casing

STEAM TURBINES - Impulse Turbine

If steam at high pressure is allowed to expand through a stationary nozzle, the result will be a drop in the steam pressure and an increase in steam velocity. In fact, the steam will issue from the nozzle in the form of a high-speed jet. If this high velocity steam is applied to a properly shaped turbine blade, it will change in direction due to the shape of the blade . The effect of this change in direction of the steam flow will be to 1: Shaft 2: Disc 3: Blade

produce an impulse force, on the blade causing it to move. If the blade is attached to the rotor of a turbine, then the rotor will revolve.

4: Nozzle Steam Turbines Introduction - 31/07/2008 - P 11 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Reaction Turbine The principle of a reaction turbine can be explained using a balloon. When the air is released from a blown balloon, it rushes out through the small opening and the balloon will shoot off in the opposite direction. When the balloon is filled with air, the potential energy is stored in the increased air pressure inside. When the air is let escape, it passes through the small opening. This represents a transformation from potential energy to kinetic

energy . The force applied to the air to speed up the balloon is acted upon by a reaction in the opposite direction. This reactive force propels the balloon forward through the air.


STEAM TURBINES - Reaction Turbine A reaction turbine has rows of fixed blades alternating with rows of moving blades. The steam expands first in the stationary or fixed blades where it gains some velocity as it drops in pressure. It then enters the moving blades where its direction of flow is changed thus producing an impulse force on the moving blades. In addition, however, the steam upon passing through the moving blades, again expands and further drops in pressure giving a reaction force to the blades.


STEAM TURBINES - Combined type turbine •

The pure Reaction turbine is not a practical type.

•

Application of Impulse and Reaction principles of operation is a practical approach.

•

Partial pressure drop and hence small increase in velocity takes pace in fixed nozzles.

•

Remaining pressure drop and change of momentum takes place in moving blades.

•

The gross propelling force is the vector sum of the impulse and reaction forces.


STEAM TURBINES - Axial Flow turbine

• Steam flows in a direction parallel to the axis of the turbine.


STEAM TURBINES - Single Flow Axial turbine

Steam Inlet

Steam Expansion

Steam flows in only one direction parallel to the axis of the turbine.


STEAM TURBINES - Double Flow Axial turbine

Steam Inlet

Steam Expansion

Steam flows parallel to the axis of the turbine and in two opposite directions. Axial forces developed due to steam flow are counter balanced.


STEAM TURBINES - Reverse Flow Axial turbine Steam Inlet Steam Expansion Steam Expansion

In this type of turbine, rotors of two cylinders are combined together. Initially steam expands in one cylinder flowing parallel to the turbine axis and then fed back to the entry of another stage with or without reheat. Steam Turbines Introduction - 31/07/2008 - P 18 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Radial Flow turbine

• Steam flows in a direction perpendicular to the axis of the turbine. Steam Turbines Introduction - 31/07/2008 - P 19 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Condensing turbine

Vertically down condensing type

To condenser

Axial condensing To condenser type

• With the condensing turbine, the steam exhausts to the condenser and the latent heat of the steam is transferred to the cooling water. The condensed steam is returned to the boiler as feed-water. Steam Turbines Introduction - 31/07/2008 - P 20 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Back Pressure turbine

• Back-pressure turbines are often used in industrial plants, the turbine acts as a reducing station between boiler and process steam header. The process steam pressure is kept constant and the generator output depends on the demand for process steam. Steam Turbines Introduction - 31/07/2008 - P 21 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Reheat turbine

• In the Reheat cycle, steam at a given initial temperature is partially expanded through the turbine (process C-D) doing some some work, and then is fed back to the boiler, where it is reheated to about original temperature (process D-E). The heated steam is then fed through the remainder of the turbine before being condensed (process E-F). • In a reheat cycle, cycle heat input is increased and hence increase in thermal efficiency. But this increases capital overlay in terms of re-heater pipe-work to, from and within boiler. Steam Turbines Introduction - 31/07/2008 - P 22 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Regenerating turbine

• In the Regenerative cycle, steam steam from different stages stages of turbine are bled and and used for heating the feed water. There will be a small loss of work available from the bled steam not expanding in the turbine; however, this loss is out-weighed by the gain in cycle efficiency.

Steam Turb Turbines ines Intro Introduct duction ion - 31/07 31/07/2008 /2008 - P 23 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Single Stage Turbine

• In a Single Stage Stage turbine, turbine, steam steam is expande expanded d in only one stage. stage. Generall Generallyy these turbines are of Impulse type with exhaust pressure higher than the atmospheric pressure.


STEAM TURBINES - Multi stage Turbine

• In this type type of turbines, turbines, steam steam is allowed allowed to pass pass through through a series of fixed fixed and moving moving blades. Total heat drop in the turbine is the sum of heat drop in each stage. They can be of Back pressure type or Condensing type. Steam Turb Turbines ines Intro Introduct duction ion - 31/07 31/07/2008 /2008 - P 25 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Single Cylinder Turbine

• In a Single cylinder turbine, entire action of steam takes place in only one cylinder. They can be either Single Stage or Multistage turbines.


STEAM TURBINES - Multi Cylinder Turbine

• In this type of turbines, steam is allowed to pass through two or more cylinders. These turbines are of higher capacity and most of the time Re-heat type. Steam Turbines Introduction - 31/07/2008 - P 27 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES

Working Concepts of Steam Turbines


STEAM TURBINES - Compounding Velocity Compounding: This is achieved by alternate rows of fixed blades and moving blades. • The high velocity steam leaving the nozzle passes on to the first stage moving blade suffers a partial velocity drop. • Direction of this steam is then corrected by the next rows of fixed blades and then the same is entered in next row of moving blade where again the velocity reduces partially. • Hence, only part of the velocity of the steam is used up in each row of moving blades.


STEAM TURBINES - Compounding The advantages of velocity compounding are: • System is easy to operate and more reliable. • As nos. of stages are less, initial cost is lower. • Since the total pressure drop takes place only in nozzles and not in the blades, the turbine casing need not be heavily built. Hence, the economy in material cost and less floor space is required.

The dis-advantages of velocity compounding are: • As the steam velocity is too high, frictional losses are also high. • Blade efficiency decreases with increase in number of stages i.e with the increase of the number of rows the power developed in successive rows of blades decreases. Whereas the same space and material are required for each stage, it means, the all the stages are not economically efficient. Steam Turbines Introduction - 31/07/2008 - P 30 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Compounding Pressure Compounding: This is achieved by an alternate rows of nozzles and moving blades. • The steam enters the first row of nozzles where it suffers a partial drop of pr. and in lieu of that its velocity gets increased. • The high velocity steam passes on to the first row of moving blades where its velocity is reduced partially. • Similarly again a pressure drop occurs in second stage nozzle and with increased velocity steam enters in second stage moving blades where again the velocity is reduced . • Thus pressure drop (partial) takes place in successive stages, the increase in velocities are not so high resulting in slow speed rise of turbine.


STEAM TURBINES - Compounding


STEAM TURBINES - Compounding

Pressure - Velocity Compounding: It is a combination of Pressure compounding and Velocity compounding. • Steam is expanded partially in a row of nozzles whereupon its velocity gets increased (due to pressure drop). • This high velocity steam then enters a few rows of velocity compounding whereupon its velocity gets successively reduced. • The velocity of steam is again increased in the subsequent row of nozzles (due to drop in pressure) and then again it is allowed to pass onto another set of velocity compounding that brings about a stage-wise reduction of velocity of the steam.


STEAM TURBINES - Thermal Cycle The efficiency of a thermal power plant can be expressed as the product of efficiencies of its sub-systems: ηthermal .plant = ηboiler (0.30 to 0.40)

(0.75 to 0.90)

ηthermal plant = ηboiler

x ηthermal cycle x ηturbine x ηmechanical x ηgenerator

=

ηthermal cycle =

(0.35 to 0.50)

(0.85 to 0.95)

(0.99 to 0.995)

(0.98 to 0.985)

Energy output (at generator terminal) Energy Input (calorific value of fuel) Energy output (total increase in enthalpy of fluid in boiler) Energy Input (calorific value of fuel) Energy output (energy available for conversion to mech. work) Energy Input (total energy/ enthalpy available in working fluid)


STEAM TURBINES - Thermal Cycle ηturbine internal =

Energy output(total enthalpy of fluid converted in mech work) Energy Input (total energy for conversion to mech work)

ηmechanical =

Energy output (work done at turbine-generator coupling ) Energy Input (total energy of fluid converted into mech work)

ηgenerator

=

Energy output (at generator terminal) Energy Input (work done at turbine - generator coupling )


STEAM TURBINES - Thermal Cycle Typical values of these efficiencies for a modern thermal power plant employing reheat and regenerative feed water heating cycle indicates: • It is evident from the above values of efficiencies that mechanical efficiency of turbine and efficiency of generator are very high (approaching to 1), • Boiler efficiency and internal efficiency of turbine are also fairly good and these are improving continuously. • The thermal cycle efficiency is lowest of all the efficiencies and is governed by the laws of thermodynamics. In order to get highest plant efficiency, it is imperative that thermal cycle efficiency should be as high as possible.


STEAM TURBINES - Thermal Cycle - Phase Transformation Liquid - Vapour Phase of Water :

•

Steam is the vapour phase of water.

•

To effect a change of state from liquid phase to vapour phase, internal energy is required.

•

In boilers, this internal energy is supplied by heat.

•

The heat required to bring about this transformation is called the latent heat of evaporation.

•

Under pressure less than 225 kg/cm2, the latent heat is absorbed by water at constant temperature, called the saturation temperature.

•

The value of latent heat decreases with rising pressure. The saturation temperature normally rises with pressure.


STEAM TURBINES - Thermal Cycle - Phase Transformation Vapour (Superheat) phase. Sp heat ≈0.5 kcal/kg

T E M P

Evaporation phase – absorbs latent heat

Liquid phase. Sp heat ≈ 1 kcal/kg

Enthalpy

♦ The specific heat of water and steam & latent heat changes with

pressure. See next graph. ♦ Evaporation takes place in furnace, boiler bank (where present), evaporation of water in spray type attemperator and at times even in economiser , if economiser is steaming. ♦ Superheat or reheat is heating in vapour phase in Superheater & reheater. ♦ Heating in liquid phase takes place in economiser (where installed). Steam Turbines Introduction - 31/07/2008 - P 38 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Thermal Cycle ( Phase Transformation) Critical point – 225 Kg/cm2g – No evaporation phase.

T E M P

Evaporation phase

Vapour (Superheat) phase.

Pr = Hi Pr = Med

Pr = Low Liquid phase.

Enthalpy

♦

Note that latent heat of evaporation reduces with increasing pressure & vanishes at critical point.


STEAM TURBINES -

Factors Affecting Thermal Cycle Efficiency

Initial Steam Pressure: At constant initial steam temperature : • Increase in initial steam pr. (means increase in saturation temp.of feed water or in mean temp. at which heat is added to the cycle). This will result in increase in thermal efficiency cycle.

However, with increase in initial steam pr. at constant temp. & constant condenser pr., wetness of steam in the last stages of turbine increases, thereby internal efficiency of these stages decreases. Usually 1% moisture increase in steam in a particular stage results in 0.9% to 1.2% decrease in turbine internal efficiency and also the erosion becomes so severe that life of the turbine is endangered.


STEAM TURBINES -

Factors Affecting Thermal Cycle Efficiency

• With increase in initial steam pr., blade height of initial stages decreases (cannot be designed below 25mm due to inefficiency and 3D flow & vortex formation).

With increase in initial pr., shell thickness increases resulting in increased stress and low rate of speeding/ loading.

In light of above considerations, lower initial steam pr. are used for smaller turbines (simple design, quicker start up) and higher steam pr. for larger turbine (higher efficiency).


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency Initial Steam Temperature: The theoretical considerations of thermodynamics it is imperative that: • As initial temp. increase, the thermal cycle efficiency increases. • However, material considerations do restrict the initial steam temp. - upto 4000 C Plain Carbon Steel can be used - upto 4800 C Low Alloy Steel can be used - upto 6000 C Resistant Ferritic/ Martensitic Steel can be used e.g: various grades of Cr-Mo-V(Ni) or Cr-Mo (Ni) ferrite steels .


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency • Hence, the initial steam temp. gives a limiting value of 5650 C (leaving margins for temp. swings).

Further due to frequent failure of boiler tubes (resulting outages) at 565 0 C, most practical (safe) limit for initial steam temp. of 540 0 C is adopted in general.

Above 5400 C temp., austenitic steels could be used, which have higher coefficient of thermal expansion & lower thermal conductivity but due to poor machineability and weldability as compared to ferrite steel, austenitic steel is not preferred.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency Reheat Cycle and Parameters: • Re-heating of steam after it has partially expanded, improves the thermal cycle efficiency by 4 to 5% as a more efficient cycle is added to original cycle. • With the reheat, available heat drop (for conversion to work) increases by approx 12% of unit mass of working fluid, resulting in almost corresponding reduction in mass flow of working fluid for generating same power output. • This results in smaller aux. Equipment (condenser, heaters, CEPs, BFPs) thus resulting in savings in investment. • Re-heating reduces moisture in last stage blades thereby improving turbine internal efficiency.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency • However, re-heating invariably complicates the design of turbine, boiler & their controls. • Thus it involves additional investment in terms of complex design, additional piping & re-heater. • If pressure drop in re-heater is more, almost all the gain in efficiency is offset.

Hence, the steam after partial expansion is usually re-heated to initial steam temp. at pr. 0.15 to 0.30 times initial pr. Absolute increase in thermal cycle and thermal plant efficiency by re-heating is approx. 1.5% to 2%.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency Regenerative Feed Water Heating Cycle: • In regenerative feed water heating part of the bled (extracted) steam after partial expansion in the turbine is used to heat up the feed water going to boiler. • In this process the latent heat of liquidation of bled (extracted) steam is utilised in heating feed water thereby increasing the thermal efficiency (would otherwise been dumped into the condenser).

• Usually feed water is heated to 0.55 to 0.75 times saturation temp. in series of heaters. As a consequence of steam extraction for feed water heating, increased steam flow through turbine is required to generate the same power.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency Usually thermal cycle employing regenerative feed water heating will have 30% higher flow at stop valves and 30% lower flow at turbine exhaust as compared to thermal cycle without regenerative feed water heating.

• This makes regenerative feed water heating even more attractive to the following reasons:

- Increase in steam flow in initial stages of turbine results in increased blades height thus improving internal thermal efficiency of turbine. - Reduced flow at turbine exhaust demands lesser exhaust area, resulting in smaller blades in last stages, which is limiting factor in turbine design.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency Condenser Vacuum: Condenser has triple function in “Rankine Cycle”, • Provide Heat Sink (Phase change of working fluid takes place) • Low Vacuum (heat rejection takes place at low temp./ thermal efficiency) • Preserve/ store working fluid (costly demineralised water) Condenser vacuum is dependent on the cooling water temp. and to some extent to cooling water flow rate. In India, cooling water temp. ranges between 240 C (for snow fed rivers) to 360 C (sea water or river waters in hot season) giving condenser pressure of 0.06 to 0.12 ata. Since, cooling water is usually taken from river, lake or sea whichever is nearby the thermal plant, we don’t have direct control over cooling water temperatures. However, we can install cooling towers at our plants to further cool this available direct cooling water of river, lake or sea and in turn can improve the condenser vacuum.


STEAM TURBINES - Factors Affecting Thermal Cycle Efficiency

Turbine Losses: Losses in turbine can be divided in two groups:

Internal: Frictional loss, loss due to leakage (heat loss), Leaving/ residual losses.

External: Bearing friction losses, Auxiliaries drive power losses, radiation losses.


STEAM TURBINES

Construction of Steam Turbines


STEAM TURBINES - Construction of Turbines


STEAM TURBINES - Construction - Arrangement of blading Arrangement of Fixed and Moving Blades


STEAM TURBINES - Construction Details •

Geometrical construction of Steam turbines vary from designer to designer.

•

In general all steam turbines have the following Assemblies / Components

 Rotor  Casing  Moving blades  Guide Blades / Nozzles/ Diaphragms  Blading Materials  Steam Sealing Arrangement  Bearings & Bearing Pedestals  Control and Stop Valves  Auxiliary systems like Lube oil System, C & I, Gland Seal system, Governing System etc.


STEAM TURBINES

Steam Turbine Rotors


STEAM TURBINES - Rotor configurations •

Different configuration of rotors.

•

Configuration depends on type of Turbine (Impulse or Reaction type), ease of manufacturability, design philosophy applied.

•

A rotor generally has: 

Coupling flanges (Integral or Shrunk on)



Journals



Thrust Collar



Gland seal



Balance Piston



Blades (mounted on Discs or direct mounted)



Discs with Radial and Facial keys



Over-speed Trip assembly



MOP impeller


STEAM TURBINES - Rotor configurations Parts of typical Turbine Rotor Blades mounted on Discs Thrust Collar

Front Gland

Rear Gland

MOP Impeller

Over-speed Trip assembly

Front Journal

Rear Journal Balance Piston

Disc Radial Key


Coupling Flange

STEAM TURBINES - Rotor configurations

 Built-up rotor  Forged disc rotor  Combined rotor  Drum type rotor  Welded rotor


STEAM TURBINES - Rotor configurations Built-up Rotor

Rotors are built up with shrunk on discs. Such rotors are simpler in manufacture, but can operate only at moderate temperatures of steam. At high temperatures of steam, stress relaxation can result in loosening of disc fastening on the rotor. Example for such rotor: 200 MW LP Turbine Rotor of LMZ design


STEAM TURBINES - Rotor configurations Forged Disc Rotor

In Forged disc rotors, the discs and shaft are machined from a single forging, and therefore , loosening of discs on the rotor in turbine operation is improbable. The diameter of the forged rotors is limited, since it is is difficult to make large size forging of sufficiently high quality. Machining of forged rotors is more intricate and time consuming. Example of such rotor: 200 MW HP turbine rotor of LMZ design.


STEAM TURBINES - Rotor configurations Combined Rotor

Combined type of rotors are employed in steam turbines where the temperature of steam can vary within wide range in a single cylinder. Example of such rotor: 200 MW IP turbine rotor of LMZ design.


STEAM TURBINES - Rotor configurations Drum type Rotor

Drum type rotors are used in HP and IP cylinders of reaction type steam turbines. In most of the cases, the rotor is a single forgings. However, in some cases, they are made by welding together a number of small sizes forging. In this type of rotors, blades are mounted on the rotor directly. Example of such rotor: 140 MW HP & IP turbine rotors of CEM design.


STEAM TURBINES - Rotor configurations Welded Rotor

Welded rotors consist of several discs welded together at the peripheral circumference.The rotor portions in this design are forgings of moderate dimensions, which makes it possible to have a homogeneous structure of metal over the volume of a rotor part and improve thermal stability. They are more stiffer and lighter than forged or built-up rotors. Example of such rotor: 500 MW LP turbine rotor of ALSTOM design. Steam Turbines Introduction - 31/07/2008 - P 62 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Couplings •

Couplings are essentially devices for transmitting torque but they may also have to allow relative angular misalignment, transmit axial thrust and ensure axial location or allow relative axial movement. COUPLINGS

FLEXIBLE COUPLINGS

SEMI-FLEXIBLE COUPLINGS


RIGID COUPLINGS

STEAM TURBINES - Flexible Couplings Claw Coupling

• They are capable of absorbing small amounts of angular misalignment as well as axial movement.

Multi-tooth Coupling

• Double flexible couplings can also accommodate eccentricity. • They need continuous lubrication. • Suitable for small to medium size,

Bibby Coupling

light/heavy load.


STEAM TURBINES - Semi-flexible Couplings • These type of couplings Semi-flexible Coupling

allow angular bending only. • They do not require any lubrication. • They consist of a bellow piece having one or more convolutions.


STEAM TURBINES - Couplings Rigid Mono-bloc Coupling

•

Rigid couplings are either integral with shaft forging (mono-bloc) or shrunk on to the shaft.

•

They are used for transmitting high torque.

• Shrunk on Coupling

When using Rigid couplings, shaft alignment must be set to ensure that the coupling bending moment forces are minimised.


STEAM TURBINES - Couplings Coupling Bolt Assembly


STEAM TURBINES

Moving Blades of Steam Turbines


STEAM TURBINES - Moving Blades

• • •

Convert Kinetic Energy and or Heat Energy of steam into Mechanical Work.

•

Size of the moving blades increases from HP turbine to LP turbine to accommodate expanding steam. The length of the last stage blade in LP turbine is a limiting factor for size of the LP turbine and hence the output .

Considered as the “Heart” of the turbine. In an Impulse turbine, no heat drop occurs in moving blades. However, heat drop do occur in the case of Reaction turbine whose extent depends on Degree of reaction.


STEAM TURBINES - Moving Blades Moving Blade Nomenclature

TENON AIRFOIL SECTION

PROFILE LENGTH

E D I S E R U S S E R P

E D I S N O I T C U S

PITCH

ROOT

TANG

NECK


SHOULDER

STEAM TURBINES - Moving Blades Moving Blade Nomenclature


STEAM TURBINES - Moving Blades Classification of Moving Blades

Based on Working Principle

Based on type of Profile

Impulse Blade

Constant Profile

Reaction Blade

Changing Profile

Based on type of Root

Based on type of Shroud

"T" Root

Without Shoulder

With Shoulder

Serrated Root Fork / Finger Root Fir Tree Root

Axial Entry


Separately Shrouded

Right Hand

Integral Shrouded

Left Hand

Free Standing

Stradle Root

Radial Entry

Based on on direction of rotation

STEAM TURBINES - Moving Blades Classification based on Working Principle

•

“Bucket” Shaped Pressure side

•

Constant flow area between two adjacent blades

Impulse Blade Steam Turbines Introduction - 31/07/2008 - P 73 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Reaction Blades

STEAM TURBINES - Moving Blades Classification based on type of Profile

Blades with constant profile Steam Turbines Introduction - 31/07/2008 - P 74 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

Blades with changing profile

STEAM TURBINES - Moving Blades Roots Classification based on type of Root

“T” Root with Shoulder

“T” Root without Shoulder

Straddle Root

Serrated Root Steam Turbines Introduction - 31/07/2008 - P 75 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Moving Blades Roots Classification based on type of Root

Fir Tree Root- Radial Entry

Fork Root

Fir Tree RootAxial Entry Steam Turbines Introduction - 31/07/2008 - P 76 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Moving Blades Roots Classification based on type of Shroud

Blade with separate Shroud

Blade with integral Shroud


Free standing Blade

STEAM TURBINES - Moving Blades Classification based Direction of Rotation

Left hand blade

Right hand blade

CCW direction

CW direction


STEAM TURBINES

Blading Materials


STEAM TURBINES - Blading Materials

• • • • • •

Shrouds Rivet pins Setting Springs Locking Piece Spacers Lacing Wires/ Damping wires


STEAM TURBINES - Blading Materials Shrouds

•

Improves the stage efficiency and the steam flow conditions in the peripheral zone.

• •

Substantially reduces the leakage loss.

•

Shroud band also decreases the bending stresses in blades.

•

Some shroud bands have fins on periphery and or on inlet side to form labyrinth gland with narrow clearances.

•

Shrouds bands are fastened to the blades by upsetting the tenons on the blades.

A shroud band combines blades into packs, thus increasing in blading stiffness.


STEAM TURBINES - Blading Materials Rivets

Rivet Pins

•

Used for locking the blades and or Locking Pieces.

•

They can be of Axial entry type or Radial entry type.

Setting Springs

Setting Spring

•

Used for providing necessary tightness during blading.

•

They are placed below the blades.


STEAM TURBINES - Blading Materials Lock piece

Lock Piece

•

In some cases, a wedge is inserted in the blade entry pocket to complete blading instead of a Lock blade.

•

Generally two Lock pieces are present in diametrically opposite directions

Spacers Spacer

•

Used for maintaining proper gap (pitch) between two adjacent blades.

• •

Generally they are buried in the blade grooves. They can be manufactured with material different than that for blades.


STEAM TURBINES - Blading Materials Lacing wire

Lacing wires

•

They are used to reduce stress due to vibrations in the blade excited by steam flow fluctuations as the blades pass the nozzles.

•

Lacing wires fitted at an anti-node provide a very effective form of dampening. However, the anti-node may exist at different positions for the different types of vibration so a compromise on the position has to be reached.

•

Lacing wires are Brazed to all the blades in the packet or to the last blades in a packet.

•

They can be of solid cylinder or hollow cylinder in shape.


STEAM TURBINES - Blading Materials Damping Wire

Damping wires

•

They are used to reduce stress due to vibrations in the blade excited by steam flow fluctuations as the blades pass the nozzles.

•

A Damping wire which is 'free fitting' is free to move within the holes. Centrifugal force throws the wire to the outside of the hole where frictional effects help dampen the vibration.

•

The disadvantage of damping wires is that heavy fretting can eventually cause the holes to widen to an extent that the rotor has to be rebladed.

•

Generally they are half round in shape.


STEAM TURBINES

Special Stages in a Steam Turbine


STEAM STE AM TURB TURBINES INES - Spe Specia ciall Sta Stages ges Curtis Stage

The nozzles, of of the convergent convergent divergent divergent type, produce produce very high steam kinetic kinetic energy, some of which is absorbed in the first row of moving blades, the remainder being deflected back by the fixed guide blades and used in the second row. Steam Turb Turbines ines Intro Introduct duction ion - 31/07 31/07/2008 /2008 - P 87 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM STE AM TURB TURBINES INES - Spe Specia ciall Sta Stages ges

• • •

Curtis Stage : It is the first stage of blades used in an Impulse or Impulse-reaction turbines. It is an impulse stage with Velocity compounding. Turbines employing Nozzle Governing arrangement, have Curtis Stage as their Regulating stage.

•

Curtis stage stage permits permits the utilisation utilisation of a large large heat drop in the nozzles and and consequently helps in obtaining lower temperature and pressures in the following stages.

•

The use of Curtis stage in an Impulse-Reaction turbine reduces the number of reaction reacti on stages and hence hence construction construction of turbine turbine becomes simple and cheap. cheap.

•

Curtis stage can have either Single row or Double rows of blades. Turbines with high initial pressures are built with double row Curtis stage.


STEAM STE AM TURB TURBINES INES - Spe Specia ciall Sta Stages ges Baumann Stage

In this design the penultimate turbine stage is divided: the steam flow through the outer annular part of the stage is led directly to the condenser, while the inner part flows through the final stage on its way to the condenser. Steam Turb Turbines ines Intro Introduct duction ion - 31/07 31/07/2008 /2008 - P 89 © ALSTOM 2007. All rights reserved. Information Information contained in this document is provided without liability for information information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information information or fitness for any particular purpose. Reproduction, Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Special Stages Baumann Stage :

• •

Baumann stage is incorporated for increasing the power output of the turbine.

• •

The increase in power of a turbine is by a factor of 1.5

•

The two parts of the moving blade in the Baumann stage have different duties, hence there is a discontinuity in the blade profile.

•

Blades in a Baumann stage are complex in nature and thus they are difficult to design and manufacture.

•

These blade do not have good vibration characteristics.

Almost 1/3rd of the entire steam flow is directed through the upper portion of Baumann stage and exhausted directly into the condenser; bypassing the last stage. At the same time, it reduces the efficiency of the turbine for the same exit velocity loss.


STEAM TURBINES

Steam Turbine Casings


STEAM TURBINES - Casings •

Stationary parts with complicated shape often varying in diameter along its length.

•

Turbine casings are pressure vessels supported at each end designed to withstand hoop stresses in transverse plane and are very stiff in longitudinal direction to maintain accurate clearance between stationary and rotating components.

•

They can be of Single Shell design or Double Shell design.

•

Generally split horizontally passing through the turbine axis. Exception being the HP inner casings of KWU design turbines which are vertically split; and HP outer casings of KWU design turbines which are not at all split.

•

Usually top and bottom halves of the casings are held together with the help of fasteners at flanges on the parting plane. Exception to this method of holding together the casing halves is HP Inner casings of ALSTOM design which are fastened with Shrink rings.

•

HP and IP casings are castings of special alloy steels while the LP casings are of fabricated type made with Carbon steel.


STEAM TURBINES - Casings

IP-LP Combined outer casings


STEAM TURBINES - Casings

HP Inner casing

IP Inner casing

LP Inner casing Steam Turbines Introduction - 31/07/2008 - P 94 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Casings IP-LP Combined outer & inner casings


STEAM TURBINES - Casings Parting Plane Fasteners PARTING PLANE FASTENERS

STUDS

DOWEL STUDS

CAP NUTS / NUTS

HP CASING

IP CASING

STUD M140 X 4-T X 810

STUD M100 X 4-T X 690

STUD M140 X 4-T X 710

STUD M100 X 4-T X 705

STUD M48 X 130

STUD M120 X 4-T X 760

STUD M76 X 4-T X 635

STUD M42 X 120

STUD M100 X 4-T X 705

STUD M42 X 120

DOWEL STUD M100 X 4-T X 930

DOWEL STUD M76 X 4-T X 870

CAPNUT M140 X 4

CAPNUT M100 X 4

CAPNUT M120 X 4

CAPNUT M76 X 4

CAPNUT M100 X 4

NUT M 42


LP CASING

NUT M 48 NUT M 42

T U R B I N E T Y P E K -2 0 0 -1 3 0 8

STEAM TURBINES - Casings Shrink Rings

Comparison of Shrink Rings & P/P Fasteners

ALSTOM Features

Customer Benefits

•

Light weight

•

Good behavior during load changes

•

No mass concentration

•

Operational flexibility to grid

•

No casing distortion

•

Horizontal separating flange


requirements •

Easy maintenance,

•

low maintenance costs

STEAM TURBINES

Stationary Blades of Steam Turbines


STEAM TURBINES - Guide blades / Nozzles/ Diaphragms

• • •

Convert Pressure Energy or Heat Energy of steam into Kinetic Energy.

•

In impulse turbine, entire heat drop of the stage happens in the stationary blades. However, in a Reaction turbine, partial heat drop occurs and the extent depends on the Degree of reaction.

•

Nozzles are the stationary blades of first stage; generally the control stage. They experience the highest temperature in the entire turbine. Generally, a large heat drop occurs in the Nozzles.

Static components. They are also called Stationary blades, Nozzle blades. In an Impulse turbine, stationary blades are embedded in Diaphragms. In a Reaction Turbine, individual blades are assembled in the casing or Blade carrier and they are called Guide blades.


STEAM TURBINES- Guide blades / Nozzles/ Diaphragms

• •

• • • •

Guide blades can be un-shrouded, separately shrouded or with integral shrouds. Diaphragms are constructed in any of the following three methods: *

By pinning the Nozzle blades onto a disc

*

By welding the Nozzle blades to outer and inner rims.

*

By sandwich casting the Nozzle blades between outer and inner rims.

Pin type diaphragms are used in small and moderate pressure turbines. Welded Diaphragms are used in High and Intermediate pressure turbines. Cast type diaphragms are used in low pressure and large turbines. Nozzles can be manufactured either by carving out material from a forged plate or by welding nozzle blades with the Nozzle body.



Guide blades with Integral Shroud

Guide blades with Separate Shroud

Un-shrouded Guide blade



Guide blades assembled in inner casing



A typical Diaphragm



Nozzle for Pin type Diaphragm

Pin type Diaphragm


A closer look of Pin type Diaphragm


Welded Type Diaphragm


Typical Cross Section of Welded Type Diaphragm


Cast Type Diaphragm Steam Turbines Introduction - 31/07/2008 - P 106 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.


Nozzle carved out from a plate


Welded type Nozzle

STEAM TURBINES

Steam Sealing


STEAM TURBINES - Steam Sealing

•

For minimizing the steam leakage and for maintaining the peak efficiency Sealing systems are used.

•

Generally Labyrinth seals are used where the shaft passes through the casing end glands and diaphragms.

•

Water sealing system and Carbon ring packing are also used for steam sealing in some designs.

•

Sealing materials are of relatively softer material and assembled concentric with the turbine shaft.

•

Sealing system generally comprises of gland box, leak off manifold, Gland condenser, air ejector and condensate tank.






STEAM TURBINES - Labyrinth Seals INTERMEDIATE GLAND SEALING


STEAM TURBINES - Labyrinth Seals END GLAND SEALING


STEAM TURBINES -

Other types of Sealing

END GLAND SEALING

A wheel forged on the rotor ends runs in a water bath. This water is flung out by centrifugal action. The gland only needs to be small as large pressure drops require little head. The system cannot be used on reversible sets and at reduced revolutions.

This type of gland comprises a number of segmental rings of graphitic carbon. The material is self lubricating. The rings are placed in a suitable housing. The rings are held close together by a spring which wrapped around the gland rings. The rotation of rings is prevented by key sunk into bottom of the gland housing. In some cases, carbon rings are actually in contact with the shaft or sleeve thereon, but in some cases definite radial clearances are maintained.

Water Seal


Carbon Seal

STEAM TURBINES

Bearings and Bearing pedestals


STEAM TURBINES -

Bearings & Bearing Pedestals

PURPOSE Bearing Pedestals The main purpose of bearing pedestals is to support the turbine rotor, via the journal bearings, in a fixed relationship to the cylinders so that gland clearances are maintained in all phases of operation. They also house the Main Oil Pump and some instrumentation.

Journal Bearing The purpose of a journal bearing is to retain the rotor system in its correct radial position, relative to the cylinders, and to provide a low friction support which will withstand static and dynamic loads of shaft rotation, together with the frictional and conducted heat, and to remain free from maintenance except at major outages.


Thrust Bearing The purpose of the turbine thrust bearing is to provide a positive axial location for the turbine rotors relative to the cylinders.

STEAM TURBINES - Bearing Pedestals

FRONT BEARING PEDESTAL Steam Turbines Introduction - 31/07/2008 - P 117 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

THRUST BEARING PEDESTAL

STEAM TURBINES - Bearing Pedestals •

Cast or Fabricated rigid construction.

•

Stiffness achieved with ample usage of ribs and gusset plates.

•

Fabricated construction has the advantage of increased support stiffness, whilst maintaining a compact overall pedestal size with good resistance to impact load.

•

Improved cast material (Spheroidal Graphite Cast) Iron is used for construction.

•

Normally pedestals in LP area are firmly bolted and doweled to the foundations.

•

At high temperature end of turbine, provision is made either for the cylinders to expand at sliding mounting points on top of their pedestals or for pedestal to slide relative to the foundations or both.

•

Pedestals near adjacent to high temperature components of the turbine are frequently protected by radiation shields.


STEA ST EAM M TU TURB RBIN INES ES - Jo Jour urna nall Be Bear arin ings gs •

Horizontally sp split at at cen centtre liline.

•

White Whi te meta metall lini lining ngss used used becau because se of hi high gh load loadin ing g capa capaci city, ty, rel relia iabi bilit lityy and absence of wear due to hydrodynamically generated films of lubricating oil. The white metal surface is either cast into a mild steel liner to form a bearing body or cast directly into the bearing body itself. Two main white metal profiles in common use are Two Lobe (Elliptical) and Three Lobe.

•

Jour Jo urna nall bear bearin ings gs for for tur turbin bines es are are usu usual ally ly for force ce lub lubri rica cated ted an and d have have provision provis ion for admitting admitting Jacking Jacking oil. The oil is continuo continuously usly fed into wedge by frictional drag and leaks away axially towards the brg edges

•

Thee bear Th bearin ings gs are are nor norma mallllyy spher spheric ical ally ly sea seated ted in thei theirr pede pedesta stals ls on on pads under which shims are placed to facilitate precise horizontal and vertical alignment of shaft line.


STEA ST EAM M TU TURB RBIN INES ES - Jo Jour urna nall Be Bear arin ings gs TYPICAL JOURNAL BEARING CONFIGURATIONS


STEA ST EAM M TU TURB RBIN INES ES - Jo Jour urna nall Be Bear arin ings gs TYPICAL CONSTRUCTION OF JOURNAL BEARING


STEAM TURBINES - Thrust Bearings •

Provides positive axial location for rotors relative to the cylinders.

•

It is designed to withstand the unbalanced thrust due to blade reaction and steam pressure acting on unbalanced areas.

•

It is normally located close to the areas where blade/cylinder clearances are minimum and operating temperatures are highest.

•

Although the net thrust on the white metalled pads in the on-load condition is always in one direction, i.e., typically towards generator, a second set of pads, termed “Surge pads”, are incorporated on the integral shaft collar. This is to take care of transient reversal of thrust which occur during load reduction and following a turbine trip.

•

The thrust bearing is generally combined with a journal bearing, housed in spherically machined steel shell.


STEAM TURBINES - Thrust Bearings TYPICAL CONSTRUCTION OF THRUST BEARING


STEAM TURBINES

Steam Chest


STEAM TURBINES - Control & Safety Valves TYPICAL CONTROL VALVE & STOP VALVE ASSEMBLY: STEAM CHEST


STEAM TURBINES - Emergency Stop Valves TYPICAL STOP VALVE ASSEMBLY


STEAM TURBINES - Control / Governor Valves TYPICAL CONTROL VALVE ASSEMBLY


STEAM TURBINES - Stop & Control Valves •

Turbines are equipped with Emergency Stop Valve (ESV) to cut off steam supply during periods of shutdown and to provide prompt interruption of the steam flow in an emergency trip.

•

The Control Valves (CV) provide accurate control of the steam flow entering the turbine, thus controlling the generator load when the machine is synchronised to the grid.

•

Steam chests can be integral with the turbine casings or separate casing connected to turbine casing by flexible pipelines.

•

Usually Steam Strainers are also housed in the steam chest, but sometimes separate casings are used to house steam strainers.

•

ESVs are actuated by servomotor controlled by the protection system. ESV remains either fully opened or fully closed.

•

CVs are operated by the governing system through servomotors to regulate steam supply as required by the load.


STEAM TURBINES -

General Considerations

Balancing: Rotors are dynamically balanced to a very high degree of precision. Anchoring: LP Casing ( heaviest part- min. movement/ expansion) is usually anchored to foundation. This anchoring can be done at front or rear pedestals or at the mid point of LP Casing. Rotors are anchored at thrust bearing w.r.to casing. Catenary of Rotors: Due to weight of rotor sag takes place which is compensated by bearing alignment (coupling flanges made parallel) in the sag shape of rotors also.


STEAM TURBINES

Material Selection in Steam Turbines


STEAM TURBINES - Material Selection •

Steam Turbine components are highly stressed as they operate at elevated temperatures, pressures and high speed.

•

Besides the design requirements metallurgical consideration are of utmost importance in the selection of materials in order to have greater reliability and good service during operation.

•

The metallurgical considerations are

 Alloying elements and their effect on: 

Structure, heat treatment, manufacturability, weldability, fatigue life and creep resistance characteristics.

 The micro-structure stability  Inter crystalline corrosion,  Embrittlement,  Effect of delta ferrite Steam Turbines Introduction - 31/07/2008 - P 131 © ALSTOM 2007. All rights reserved. Information contained in this document is provided without liability for information purposes only and is subject to change without notice. No representation or warranty is given or to be implied as to the completeness of information or fitness for any particular purpose. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.

STEAM TURBINES - Material Selection Criteria for selection of materials depends on •

Physical characteristics

     •

Thermal co-efficient of expansion Thermal conductivity Modulus of Elasticity Poison’s ratio Density

Mechanical properties

      

Hot yield strength Creep & rupture strength Stress relaxation properties Cyclic loading behaviour Fracture Toughness Rate of crack growth Resistance to scaling


STEAM TURBINES - Physical Characteristics of Materials • At elevated temp. thermal conductivity is important for quick dissipation/ absorption of heat thus minimising thermal stresses. • Thermal co-efficient of expansion (elongation/ diff.temp.) and the modulus of elasticity (stress/strain) are important because these play an important role in inducting thermal stresses and ensuring the design clearance and their minimum values are favorable. • Poisons ratio : Ratio between the value of transverse compression and longitudinal elongation within the limits of elastic strain, taken for the case of simple tension in one direction. • Density : mass (gm or kg) per unit volume (cm 3 or m3 ) is density.


STEAM TURBINES - Mechanical Properties of Materials *Hot Yield (0.2% proof/ yield stress): At high temp. but not in creep range 6500C( 62Kg/mm2). Hot yield of a steel decreases with an increase in temp.

* Creep and Rupture Strength:The gradual deformation under the action of constant load at a constant elevated temperature is called creep.The gradual strain is called creep strain. * Creep Relaxation properties: There are certain high temp. components in which the stress does not remain constant but decreases with time at elevated temp. due to creep (elastic strain changes into plastic strain - hence relaxes stress require re-tightening).

* Cyclic Loading behaviour: The components which are working at elevated temp. under static and cyclic loading are subjected to creep fatigue due to combined stresses.


STEAM TURBINES - Mechanical Properties of Materials * Fatigue behaviour : Fatigue under alternative cyclic (low or high) stresses. * Fracture Toughness: Resistance of material to fast fracture in presence of defects.

* Rate of crack growth : Rate of propagation of defects due to cyclic stresses during operation of turbine. * Resistance to Scaling :Scaling r educes effective thickness / area of heat transfer. * Metallurgical Stability: No change in grain structure during long term operation. * Corrosion & Erosion Resistance: To achieve the same various grades of CrMo-V or Cr-Mo ferrite steels are used according to weldability and hardness.


STEAM TURBINES - Important Terms Heat Rate/ Specific Heat Consumption: Required heat input for per unit power generation (KCal / KWHr). Enthalpy: Available Heat energy per Kg of working fluid (KCal / Kg)

Plant Load Factor: Ratio of generated energy to the available (rated) energy for generation. Availability: Unit available for rated power generation. Specific Steam Consumption: Consumption of steam (Kg) for unit power generation (Kg / KWHr )


STEAM TURBINES

LP Rotor Lifting at PSWS


STEAM TURBINES Rotor Lifting Bush Arrangement

METALLIC LIFTING SLINGS (SIMPLIFIED REPRESENTATION)

210 MW LP ROTOR LIFTING BUSH ASSEMBLY


(ONLY A PART SHOWN)

STEAM TURBINES Rotor Lifting Bush Design Design Highlights: •

Fully fabricated structure.

•

High stiffness with light weight and simple construction.

•

Easy to manufacture and to use.



Finite Element Analysis employed for design.

•

Designed with optimum Factor of Safety.



Safety of Rotor shaft also calculated.


STEAM TURBINES Rotor Lifting and Disc removal Operation


STEAM TURBINES - Manufacturers The major players in Steam Turbine Manufacturing and their installed set rating in India are given below:

- General Electric, USA - Siemens, Germany - LMZ, Russia - Skoda, Czech Republic - Toshiba / Hitachi/ MHI/ Sihn Nippon , Japan - BHEL, India - ALSTOM (Germany, UK, France, Poland, Switzerland )


STEAM TURBINES - ALSTOM’s Manufacturing Units * Berlin/ Mannheim, Germany : ( 68 - 74MW - Renusagar, 149MW Anta, 250 MW NLC STCMS, 500MW NTPC Talcher) * Rugby, United Kingdom: ( 67.5MW - Balco, 500MW - NTPC Rihand) * Belford/ Velizy, France: (140MW -Nasik, 109MW Kawas) * Elblag, Poland: (66MW SAIL Bokaro & Durgapur, 120MW -Koradi), 225MW Gandhar * Baden, Switzerland : (53.5MW Hazira)


STEAM TURBINES - ALSTOM - OEM Designs

The lead centers for various design turbines installed in India are as follows: *

Berlin/ Mannheim, Germany : Berlin, Mannheim, Ansaldo (BBC License).

*

Rugby, United Kingdom: AEI, EE, GEC, GEC Alsthom, AKZ, Toshiba, Parsons,

*

Belford/ Velizy, France: Alsthom, CEM, Rateau, SACM, Soget, TWOAX

*

Elblag, Poland: Zamech, LMZ, TMZ, Ch TGZ


Stork.

STEAM TURBINES - ALSTOM - OEM Designs

*

Milan, Italy

: Ansaldo, Tosi

*

Baden, Switzerland

: BBC (IT, KT), DGI, MFO, SEW

*

Budapest, Hungry

: Lang, G& V

*

Richmond, USA

: GE,WH, AC

*

Plzen, Czech Republic : Skoda


STEAM TURBINES - Types of orders executed * Service : - Overhauls / Inspections: Major/ Minor/ Supervisory, OEM / Third party * Repair : - At site or At works - normal (regular)/ critical * CA or RLA: - At site or At works - normal/ regular or critical * Spares Supply:

- Fast moving and noble parts, OEM / Third party, original drg. / reverse engg.


alstom

Recommend Documents