BASICS OF STEAM TURBINES

PRESENTED BY PREM BABOO

SR. MANAGER (PROD)NATIONAL FERTILIZERS LTD.,INDIA

STEAM TURBINES

WHAT IS STEAM TURBINE

STEAM TURBINE IS A DEVICE THAT CONVERTS POTENTIAL ENERGY OF

HIGH PRESSURE , HIGH TEMPERATURE STEAM INTO KINETIC ENERGY. THIS

KINETIC ENERGY IS SUPPLIED TO THE ROTARY BLADE WHERE IT IS

TRANSFORMED INTO MECHANICAL ENERGY.

THIS MECHANICAL ENERGY IS USED TO DRIVE ROTATING EQUIPMENTS LIKE

PUMPS , COMPRESSORS , FANS , BLOWERS ETC.

WHY STEAM TURBINE PREFERRED IN PROCESS PLANT ?

LOT OF STEAM IS AVAILABLE AT HIGH PRESSURE AND

TEMPERATURE BECAUSE OF RECOVERY OF WASTE HEAT

GENERATED AS A RESULT OF VARIOUS EXOTHERMIC

REACTIONS TAKING PLACE IN PROCESS.

ADVANTAGES OF STEAM TURBINES

THERMODYNAMIC EFFICIENCY IS MORE. DUE TO ABSENCE OF RECIPROCATING PARTS , THE

VIBRATIONS ARE GREATLY MINIMIZED AND THE MACHINE CAN BE ACCURATELY BALANCED.

NO RUBBING PARTS HENCE NO INTERNAL LUBRICATION IS REQUIRED.

ABOVE POINT ENSURES THE SUPPLY OF PURER FEED WATER TO THE BOILER.

LESS MAINTENANCE AS COMPARED TO OTHER PRIME-MOVERS.

Steam TurbineAn Important Prime Mover in

ExistencePrinciple: The working of The Turbine wholly depends upon the

Dynamic Action of the Steam Steam is caused to fall in pressure in a passage

called NOZZLE Due to this a certain amount of heat energy is

concerted into MECHANICAL KINETIC ENERGY Steam is set moving with GREAT VELOCITY Rapidly moving steam enter the moving part of the

turbine & suffer A CHANGE IN DIRN. OF MOTION This leads to a CHANGE OF MOMENTUM &

THEREFORE TO A FORCE THIS CONSTITUTES THE DRIVING FORCES OF

THE MACHINE

STEAM INSTEAM OUT

FORCE

PRINCIPLE OF STEAM TURBINE

Types of TurbineBased on Principle

Impulse TypePressure CompoundedVelocity CompoundedPressure Velocity Compounded

Impulse Reaction Type

(I) SIMPLE IMPULSE:

The passage of steam through the moving part of the Turbine (Blade) may take place in a manner that the pressure at the outlet side of the blade is equal to that at the Inlet Side.

SIMPLE IMPULSE TURBINE IS NOT SO COMMON

• SINCE THE WHOLE PRESSURE DROP TAKES PLACE IN SINGLE ROW OF NOZZLES , THE VELOCITY OF THE STEAM ENTERING THE TURBINE IS VERY HIGH.IF THIS VELOCITY IS UTILIZED IN SINGLE ROW OF TURBINE BLADES , THE SPEED OF ROTATION OF WHEEL WILL BE TOO HIGH TO BE USEFUL FOR PRACTICAL PURPOSES, AS THERE IS THE DANGER OF STRUCTURAL FAILURES DUE TO EXCESSIVE CENTRIFUGAL STRESSES.• STEAM EXITS FROM THE TURBINE WITH SUFFICIENTLY HIGH VELOCITY , MEANING A CONSIDERABLE LOSS OF KINETIC ENERGY.

COMPOUNDING OF IMPULSE TURBINE

DEVELOPMENT OF STEAM TURBINES LEAD TO COMPOUNDING WHEREBY SPEED OF ROTATION IS REDUCED AND AT THE SAME TIME FULL AVAILABLE ENERGY IS UTILIZED.THIS ALLOWS PRODUCTION OF TURBINES OF LARGER SIZE AND HIGHER POWER OUTPUT. THIS IS ACHIEVED BY :VELOCITY COMPOUNDING :- CONVERTING THE TOTAL ENTHALPY FALL INTO K.E IN ONE STAGE BUT DIVIDING THE CONVERSION OF K.E OF STEAM INTO MECHANICAL ENERGY OF THE WHEEL IN PORTIONS.

VELOCITY COMPOUNDING

ADVANTAGES OF VELOCITY COMPOUNDING

•HAVE FEWER NUMBER OF STAGES HENCE LESS INITIAL COST•THE ARRANGEMENT RQUIRES LITTLE SPACE•THE SYSTEM IS EASY TO OPERATE.•THE PRESSURE DROP IN THE NOZZLE IS CONSIDERABLE , SO THE TURBINE ITSELF NEED NOT WORK IN HIGH PRESSURE SURROUNDINGS AND THE TURBINE HOUSING NEED NOT TO BE VERY STRONGLY MADE.

PRESSURE COMPOUNDING

COMBINED IMPULSE TURBINE

REACTION TURBINE

IMPULSE VERSUS REACTION TURBINES

*IN IMPULSE TURBINE THE FLUID IS COMPLETELY EXPANDED IN THE NOZZLE AND IT REMAINS AT CONSTANT PRESSURE DURING ITS PASSAGE THROUGH THE ROTOR BLADES. IN REACTION TURBINE THE FLUID IS PARTIALLY EXPANDED IN THE NOZZLE, THE REMAINING EXPANSION TAKES PLACE IN THE ROTOR BLADES.*IMPULSE TURBINE HAVE THE SAME PRESSURE ON THE TWO SIDES OF THE ROTOR BLADES, WHEREAS DIFFERENT PRESSURE EXISTS ON THE TWO SIDES OF THE MOVING BLADES OF A REACTION TURBINE.

IMPULSE VERSUS REACTION TURBINES

*IMPULSE BLADES ARE OF THE PLATE OR PROFILE TYPE AND ARE SYMMETRICAL , REACTION TURBINE BLADES ARE AEROFOIL SECTION AND ARE ASYMMETRICAL.*BECAUSE OF SMALL PRESSURE DROP IN EACH STAGE , THE NUMBER OF STAGES REQUIRED FOR A REACTION TURBINE ARE MUCH GREATER THAN THOSE FOR AN IMPULSE TURBINE.

RV.

T

LP Header

I/L

T

Condensate

I/L

COND

Classification Based on Exhaust

1) Back Pr. Type

2) Condensing Type

LOSSES IN STEAM TURBINE

•RESIDUAL VELOCITY LOSSES•LOSSES DUE TO FRICTION•LEAKAGE LOSS•LOSS DUE TO MECHANICAL FRICTION•RADIATION LOSS•LOSS DUE TO MOISTURE

STANDARDSAPI 611 : STEAM TURBINES FOR GENERAL PURPOSE : DEFINED AS “ THOSE HORIZONTAL OR VERTICAL TURBINE USED TO DRIVE EQUIPMENTS THAT USUALLY IS SPARED,IS RELATIVELY SMALL IN SIZE(POWER), OR IS IN NON CRITICAL SERVICE.

API 612 : STEAM TURBINES FOR SPECIAL PURPOSE : “THOSE HORIZONTAL TURBINE USED TO DRIVE EQUIPMENTS THAT USUALLY IS NOT SPARED,IS RELATIVELY LARGE IN SIZE(POWER), OR IS IN CRITICAL SERVICE.

SAFETY DEVICES ON TURBINES Emergency Governor: When Turbines speed

exceeds rated speed by approximately 10%, it trips the unit

Thrust Bearing Safety Device: Acts on high axial displacement

Low Lube Oil Pressure: Comes into action when pressure falls below low pressure setting.

Vacuum Device: Upon raising of Pressure in condenser

High Vibration: When vibration level goes high(up to trip setting) turbine trips.

STARTING THE TURBINE Oil Supply Condensing System Opening the Live Steam Valve Opening of Emergency Stop Valve and Control Valve Bringing the Turbine upto Speed Speed Governor takes over Main Oil Pump takes over Automatic Oil Pump control Oil Cooling

DANGER SIGNALS

Unusual Vibration Noisy Bearings Abnormally Hot Bearings Oil Rings not Turning Discoloured Oil Low Oil Pressure Excessive Gland Leakage Broken Lubricators Governor Hunting

PROTECTION SYSTEMGeneral Purpose Turbines

Constant Speed Governor Over – Speed Tripping Device Relief Valve in Exhaust Casing Relief Valve

Special Purpose Turbines Low Lub. Oil Pressure Trip High Brg. Temp. Trip High Vibn. Trip High Axial Disp. Trip Const. Speed Governor Relief Valve in Exhaust

WHAT TO CHECK FOR IN RUNNING TURBINES

Noise Levels Leakage from Glands Vibration at Bearing Housings Bearing Temperatures Movement of Oil Rings of Sleeve Bearings Governor Oil Level (for Oil Relay Governors)

Principle Components of a Steam Turbine

Casing Shaft Blading (Moving and Fixed) Supports Bearings Governing System with Regulating Valves Shaft Sealing

FEW PHOTOGRAPHS