STEAM STEAM TURBINESTURBINES

What is Steam TurbineWhat is Steam Turbine

Steam turbine is a machine Steam turbine is a machine capable of transforming thermal capable of transforming thermal energy (from steam) to energy (from steam) to mechanical energy.mechanical energy.

ORORSteam Turbine is a prime mover Steam Turbine is a prime mover in which, heat energy is in which, heat energy is transformed into mechanical transformed into mechanical energy.energy.

Purpose of Steam Purpose of Steam TurbinesTurbines

Broadly speaking, Purpose of Steam Broadly speaking, Purpose of Steam turbines is divided into two broad turbines is divided into two broad categories: categories:

Generating Electric PowerGenerating Electric Power General - Purpose units used for General - Purpose units used for

driving pumps, compressors etc. driving pumps, compressors etc.

In both cases Steam Turbine will act In both cases Steam Turbine will act as a prime mover.as a prime mover.

Principle of WorkingPrinciple of Working

When Steam is passed through a When Steam is passed through a nozzle, it expands (transforming nozzle, it expands (transforming pressure into velocity). This high pressure into velocity). This high velocity (momentum) steam, when velocity (momentum) steam, when impinges on the blades, cause the impinges on the blades, cause the wheel (rotor) to revolve. wheel (rotor) to revolve.

Types of Steam TurbineTypes of Steam Turbine

Steam turbines are categorized by the Steam turbines are categorized by the following three different ways: following three different ways:

From working principle From working principle Impulse TurbineImpulse Turbine Reaction TurbineReaction Turbine

From number of steagesFrom number of steages Single stage turbineSingle stage turbine Multi stage turbineMulti stage turbine

Types of Steam TurbineTypes of Steam Turbine

From how steam is utilized From how steam is utilized Condensing turbineCondensing turbine Back pressure (non-condensing) turbineBack pressure (non-condensing) turbine Extraction turbineExtraction turbine Induction turbineInduction turbine

Impulse PrincipleImpulse Principle

If steam at high pressure is allowed to If steam at high pressure is allowed to expand through a stationary nozzle, the expand through a stationary nozzle, the result will be a drop in steam pressure result will be a drop in steam pressure and an increase in steam velocity. If and an increase in steam velocity. If the direction of this high velocity steam the direction of this high velocity steam changed by passing it through a changed by passing it through a properly shaped turbine blade, will properly shaped turbine blade, will generate an impulse force. This generate an impulse force. This impulse force will cause the blade to impulse force will cause the blade to move.move.

Impulse PrincipleImpulse Principle

Steam In

Steam Out

Impulse

Force

Impulse Blade

Reaction PrincipleReaction Principle

When high pressure steam is When high pressure steam is allowed to expand through a nozzle. allowed to expand through a nozzle. It will produce a reaction force in It will produce a reaction force in the opposite direction. Causing the the opposite direction. Causing the blade to move.blade to move.

Reaction PrincipleReaction Principle

Steam

Out

Reaction

Force

Single Stage TurbineSingle Stage Turbine

This type of turbine intakes and This type of turbine intakes and expands the steam in a single row of expands the steam in a single row of nozzles and the kinetic (velocity) energy nozzles and the kinetic (velocity) energy of steam is converted into a mechanical of steam is converted into a mechanical one, by one or two rows of buckets.one, by one or two rows of buckets.

Single stage turbines are used mainly Single stage turbines are used mainly for small output service, such as driving for small output service, such as driving a pump. a pump.

Single Stage TurbineSingle Stage Turbine

Multi-stage TurbineMulti-stage Turbine

A multistage turbine consists of a series of A multistage turbine consists of a series of stages arranged on a single shaft. It is designed stages arranged on a single shaft. It is designed so that each stage shares only a part of the total so that each stage shares only a part of the total pressure difference. Each stage has a set of pressure difference. Each stage has a set of nozzle rows and bucket rows and is arranged in nozzle rows and bucket rows and is arranged in series to expand the steam by turns.series to expand the steam by turns.

These turbines are energy efficient and used for These turbines are energy efficient and used for medium to large power service to drive large medium to large power service to drive large pumps, compressors and (electric) power pumps, compressors and (electric) power generators.generators.

Multi-stage TurbineMulti-stage Turbine

Condensing TurbineCondensing Turbine

A condensing turbine intakes high-pressure A condensing turbine intakes high-pressure steam and expands it fully through the steam and expands it fully through the series of stages to vacuum and exhausts it series of stages to vacuum and exhausts it to a condenser, where it is condensed to to a condenser, where it is condensed to water, instead of being released to the water, instead of being released to the atmosphere or low pressure steam system. atmosphere or low pressure steam system. A condensing turbine require less steam A condensing turbine require less steam than a back-pressure turbine because the than a back-pressure turbine because the recovered energy from a unit of steam can recovered energy from a unit of steam can be maximized by expanding to high be maximized by expanding to high vacuum.vacuum.

Condensing TurbineCondensing Turbine

Back Pressure TurbineBack Pressure Turbine

A back pressure turbine (non-A back pressure turbine (non-condensing turbine) utilizes only a condensing turbine) utilizes only a part of high-pressure steam by part of high-pressure steam by expanding it to an appropriate level of expanding it to an appropriate level of pressure (low pressure or medium pressure (low pressure or medium pressure steam). Remaining energy in pressure steam). Remaining energy in the exhaust steam will be utilized as a the exhaust steam will be utilized as a heat source in the refinery. heat source in the refinery.

Back Pressure TurbineBack Pressure Turbine

Extraction / Induction Extraction / Induction TurbineTurbine

The Extraction Turbine, a part of the The Extraction Turbine, a part of the expanding steam is extracted from the expanding steam is extracted from the turbine casing at each connection and turbine casing at each connection and supplied to the steam header of supplied to the steam header of intermediate pressure. intermediate pressure.

The Induction Turbine, intermediate The Induction Turbine, intermediate nozzles are provided to induce the nozzles are provided to induce the excess steam from the steam header and excess steam from the steam header and expand it to the lower pressure level. expand it to the lower pressure level.

Extraction TurbineExtraction Turbine

Parts of TurbineParts of Turbine

High Pressure Parts:High Pressure Parts: Governor ValveGovernor Valve Trip Valve – Trip & Throttle ValveTrip Valve – Trip & Throttle Valve Steam ChestSteam Chest NozzlesNozzles

Low Pressure Parts:Low Pressure Parts: CasingCasing BladesBlades SealsSeals

Parts of TurbineParts of Turbine Exhaust HoodExhaust Hood Glands or SealsGlands or Seals

Rotor AssemblyRotor Assembly Blades or bucketsBlades or buckets DisksDisks ShaftShaft

Other PartsOther Parts Bearings (Radial & Thrust)Bearings (Radial & Thrust) Turning GearTurning Gear

Purpose of GovernorPurpose of Governor

The purpose of Governor is to The purpose of Governor is to control the speed of the turbine control the speed of the turbine according to the required load / according to the required load / set point.set point.

Governor controls the speed of Governor controls the speed of turbine by controlling the flow of turbine by controlling the flow of steam into the turbine.steam into the turbine.

Types of GovernorTypes of Governor

There are several types of governors There are several types of governors used in Steam Turbines.used in Steam Turbines.

Fly Ball GovernorFly Ball Governor Hydraulic GovernorHydraulic Governor Oil Relay GovernorOil Relay Governor Electronic GovernorElectronic Governor

Fly Ball GovernorFly Ball Governor

It consists of a fly ball and governor It consists of a fly ball and governor spring. As the speed of turbine spring. As the speed of turbine changes, the fly ball moves outward changes, the fly ball moves outward or inward because of centrifugal or inward because of centrifugal force. This creates tension in the force. This creates tension in the spring that in turns opens and spring that in turns opens and closes the steam regulation valve.closes the steam regulation valve.This phenomena in shown in This phenomena in shown in following figure.following figure.

Hydraulic GovernorHydraulic Governor

It uses an oil pump in place of fly ball. An It uses an oil pump in place of fly ball. An Oil pump is connected directly to the Oil pump is connected directly to the turbine shaft. As the turbine shaft speed turbine shaft. As the turbine shaft speed changes, the discharge pressure of the changes, the discharge pressure of the oil pump changes. Governor valve is oil pump changes. Governor valve is connected to a flexible diaphragm. As the connected to a flexible diaphragm. As the oil pressure on diaphragm changes, the oil pressure on diaphragm changes, the Governor valve opening changes as well.Governor valve opening changes as well.This governor is sensitive to temperature This governor is sensitive to temperature because of Oil.because of Oil.

Oil Relay GovernorOil Relay Governor

These governors combines the features of These governors combines the features of both fly ball governor and hydraulic both fly ball governor and hydraulic governor. Oil pressure operates the piston governor. Oil pressure operates the piston which is attached to the spring. The which is attached to the spring. The spring keeps the piston in place until a spring keeps the piston in place until a change in oil pressure acts on the piston. change in oil pressure acts on the piston. Fly ball position the pilot valve that Fly ball position the pilot valve that controls the oil flowing through oil inlet controls the oil flowing through oil inlet and oil outlet of the oil relay.and oil outlet of the oil relay.It is not sensitive to temperature as the fly It is not sensitive to temperature as the fly ball adjusts the turbine speed.ball adjusts the turbine speed.

Electronic GovernorElectronic Governor

In these Governors an Electric In these Governors an Electric Generator is attached to the Generator is attached to the turbine shaft to adjust the oil turbine shaft to adjust the oil relay. Changes in the speed of relay. Changes in the speed of shaft changes the output of the shaft changes the output of the electric current. This change in electric current. This change in the electric current adjust the the electric current adjust the pilot valve of the relay.pilot valve of the relay.

Turbine ProtectionTurbine Protection

For the protection of turbine from over For the protection of turbine from over speeding, an over speed trip mechanism is speeding, an over speed trip mechanism is provided. This mechanism operate automatically provided. This mechanism operate automatically if the speed exceeds the designed limit.if the speed exceeds the designed limit.

The over speed trip pin assembly is contained in The over speed trip pin assembly is contained in the trip body mounted on the turbine rotor the trip body mounted on the turbine rotor shaft. When the turbine speed exceeds the rated shaft. When the turbine speed exceeds the rated operated speed, centrifugal force exerted on the operated speed, centrifugal force exerted on the trip pin increases. As this force increases above trip pin increases. As this force increases above the tension in the spring of trip pin. The pin the tension in the spring of trip pin. The pin moves outward and strikes the over speed trip moves outward and strikes the over speed trip lever and thus stops the turbine.lever and thus stops the turbine.

Auxiliary SystemsAuxiliary Systems

Steam turbines are usually equipped Steam turbines are usually equipped with following auxiliary systemswith following auxiliary systems

Lubrication systemLubrication system Sealing steam systemSealing steam system

Steam Nozzl

e Stationary Blade

Moving

Blade

Lubrication SystemLubrication System

There are mainly two types of turbine There are mainly two types of turbine lubrication systemslubrication systems

Oil Ring Lubrication systemOil Ring Lubrication system Forced Lubrication SystemForced Lubrication System

First one is simple system that First one is simple system that employs oil rings to deliver oil to the employs oil rings to deliver oil to the turbine bearings.turbine bearings.Second one employs a lubrication Second one employs a lubrication pump to deliver oil to the turbine pump to deliver oil to the turbine bearings.bearings.

BearingsBearings

Two types of bearings are mainly used Two types of bearings are mainly used in the turbine,in the turbine,

Radial Bearing or Journal BearingRadial Bearing or Journal Bearing Thrust BearingThrust Bearing

Radial bearing is used to avoid radial Radial bearing is used to avoid radial vibration (up & down vibration) of the vibration (up & down vibration) of the turbine shaft.turbine shaft.

Thrust bearing is used to avoid axial Thrust bearing is used to avoid axial movement of the turbine shaft.movement of the turbine shaft.

Start Up of TurbineStart Up of Turbine

Following are the main steps involved in Following are the main steps involved in the start up of steam turbine,the start up of steam turbine,

Lubrication system preparation & start upLubrication system preparation & start up Turbine condensing system start up (optional)Turbine condensing system start up (optional) Turbine sealing & vacuum system start up Turbine sealing & vacuum system start up

(optional)(optional) Heating & pressurizing of steam lines and Heating & pressurizing of steam lines and

turbineturbine Process system preparationProcess system preparation Start up & ControlStart up & Control

Preparation & PrecautionsPreparation & Precautions

Monitoring Parameters Monitoring Parameters During OperationDuring Operation

Excessive Casing PressureExcessive Casing Pressure Condensation of SteamCondensation of Steam Quality of SteamQuality of Steam Bowing of ShaftBowing of Shaft Healthiness of the Instruments & Healthiness of the Instruments &

FittingsFittings VibrationsVibrations Contamination of the oil systemContamination of the oil system Seals leakageSeals leakage Critical SpeedCritical Speed

Shut Down of Steam Shut Down of Steam TurbineTurbine

Following are the main steps involved in the Following are the main steps involved in the start up of steam turbine,start up of steam turbine,

Lowering of Speed to minimum controllableLowering of Speed to minimum controllable Stop the turbine with shutdown push buttonStop the turbine with shutdown push button Isolation of the steam inlet and outlet valvesIsolation of the steam inlet and outlet valves Opening of all drain pointsOpening of all drain points Barring of turbine for some timeBarring of turbine for some time Cooling and shutdown of auxiliary systemsCooling and shutdown of auxiliary systems