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Steam turbine summaryWhat is the turbine?What is the principle of steam turbine?Types of steam turbine.Component of steam turbine.Problems in steam turbine.

What exactly is the turbine? Turbine is an engine that converts energy of fluid into mechanical energy

The steam turbine is steam driven rotary engine.

Principle of steam turbine:The steam energy is converted mechanical work by expansion through the turbine.Expansion takes place through a series of fixed blades(nozzles) and moving blades.In each row fixed blade and moving blade are called stage.

5Steam turbine:Widely used in CHP(combined heat and power) applications.Oldest prime mover technologyCapacities: 50 kW to hundreds of MWsThermodynamic cycle is the Rankin cycle that uses a boilerMost common types Back pressure steam turbine Extraction condensing steam turbineSteam Turbine System:56Steam exits the turbine at a higher pressure that the atmosphericBack Pressure Steam TurbineFuelFigure: Back pressure steam turbineAdvantages:Simple configurationLow capital costLow need of cooling water High total efficiency

Disadvantages:Larger steam turbineBoilerTurbineProcessHP SteamCondensateLP Steam

Steam turbine:67Steam obtained by extraction from an intermediate stageRemaining steam is exhaustedRelatively high capital cost, lower total efficiencyExtraction Condensing Steam TurbineBoilerTurbineProcessHP SteamLP SteamCondensateCondenser

FuelFigure: Extraction condensing steam turbineSteam turbine:7

steam turbine and blades

Types of steam turbine:There are two main types Impulse steam turbineReaction steam turbine

Impulse steam turbine:The basic idea of an impulse turbine is that a jet of steam from a fixed nozzle pushes against the rotor blades and impels them forward.The velocity of steam is twice as fast as the velocity of blade.Pressure drops take place in the fixed blade (nozzle).

The single stage impulse turbine:The turbine consists of a single rotor to which impulse blades are attached.The steam is fed through one or several convergent nozzles.If high velocity of steam is allowed to flow through one row of moving blades.It produces a rotor speed of about 30000 rpm which is too high for practical use.

Velocity diagram:

Cross section view:

Component of impulse steam turbine:Main components areCasingRotorBladesStop and control valveOil befell, steam befell governorBearing(general and thrust bearing)Gear box(epicyclic gear box)Oil pumps

Construction of steam turbines

1 steam pipeline2 inlet control valve3 nozzle chamber4 nozzle-box5 outlet6 stator7 blade carrier8 casing9 rotor disc10 rotor 11 journal bearing13 thrust bearing14 generator rotor15 coupling16 labyrinth packing19 steam bleeding (extraction)21 bearing pedestal22 safety governor 23 main oil pump24 centrifugal governor25 turning gear29 control stage impulse bladingReaction steam turbine:A reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. Actually, the steam is directed into the moving blades by fixed blades designed to expand the steam. The result is a small increase in velocity over that of the moving blades.

Schematic diagram:

Problems in steam turbine:Stress corrosion carkingCorrosion fatiguePittingOil lubricationimbalance of the rotor can lead to vibration misalignmentThermal fatigue

BLADE FAILURES:Unknown 26%Stress-Corrosion Cracking 22%High-Cycle Fatigue 20%Corrosion-Fatigue Cracking 7%Temperature Creep Rupture 6%Low-Cycle Fatigue 5%Corrosion 4%Other causes 10%

Corrosion:Resultant damage:Extensive pitting of airfoils, shrouds, covers, blade root surfaces.Causes of failure:Chemical attack from corrosive elements in the steam provided to the turbine.Creep:Resultant damage:Airfoils, shrouds, covers permanently deformed.Causes of failure:Deformed parts subjected to steam temperatures in excess of design limits.Fatigue:Resultant damage:Cracks in airfoils, shrouds, covers, blade roots.Causes of failure: Loosing of parts (cover, tie wire, etc.) Exceeded part fatigue life design limit

Stress Corrosion Cracking:Resultant damage:Cracks in highly stressed areas of the blading.Causes of failure:caused by the combined presence of corrosive elements and high stresses in highly loaded locations.

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