Steam turbine

Gentech Design Center1

INTRODUCTIONINTRODUCTION

Gentech Design Center 2


A STEAM TURBINE ESSENTIALLY CONSISTS OF A FOLLOWING PARTS

Major Parts



COMPONENTS OF STEAM TURBINES

Casing (Cast Steel)Casing (Cast Steel) Nozzle Block (11% - 13% Cr. Steel for Nozzles)Nozzle Block (11% - 13% Cr. Steel for Nozzles) Rotor (Wheel with sets of rotating blades – 11% - 13% Rotor (Wheel with sets of rotating blades – 11% - 13%

Cr. Steel for blades)Cr. Steel for blades) Glands (carbon rings / labyrinths)Glands (carbon rings / labyrinths) Bearings (Journal / anti-frictionBearings (Journal / anti-friction Thrust Bearings (Tilting Pad / anti-friction)Thrust Bearings (Tilting Pad / anti-friction) Over Speed DeviceOver Speed Device GovernorGovernor Governor ValveGovernor Valve Emergency Steam Stop ValveEmergency Steam Stop Valve


A) CASING

a)a) Generally Turbine casings are used for split horizontal Generally Turbine casings are used for split horizontal

and vertical position.The casing houses the bladed rotor and vertical position.The casing houses the bladed rotor

Nozzles, Diaphrams. Nozzles, Diaphrams.

b)b) It also holds glands for steam sealing each end for It also holds glands for steam sealing each end for

preventing leakage of steam.preventing leakage of steam.

c)c) Steam casing are generally of cast steel of BS 3100 Steam casing are generally of cast steel of BS 3100

B2/A2.It can stand with temperature. 400oC.B2/A2.It can stand with temperature. 400oC.


B) NOzzLES

In the nozzle stam is expanded from ahigh pressure to In the nozzle stam is expanded from ahigh pressure to

low pressure. Thus a certain amount of heat energy is low pressure. Thus a certain amount of heat energy is

converted into kinetic energy.converted into kinetic energy.

C) BLAdES

The Steam with high velocity flows over curved blades The Steam with high velocity flows over curved blades

and its direction of motion changed. The Blades which and its direction of motion changed. The Blades which

change the directiuo of steam issuing from nozzles.This change the directiuo of steam issuing from nozzles.This

causes a change of momentum and force thus causes a change of momentum and force thus

developed devices the turbine shaft. Material Of developed devices the turbine shaft. Material Of

Construction : 21cr mov 57Construction : 21cr mov 57Gentech Design Center 8

TURBINE ROTOR

Design: The Turbine rotor consists of three principal portions: Front

Portion (1 to 6); Blading Portion (7 to 9) and Rear Portion (10 to 14)



d) governor

Governor is a device, Which senses the speed of Governor is a device, Which senses the speed of

turbine and controls the steam to the turbine to maintain turbine and controls the steam to the turbine to maintain

the speed at a desired level to meet changes in load the speed at a desired level to meet changes in load

(or) steam flow.(or) steam flow.


Speed Setting Mech.

Speed Governer. Transducer Control Valve Actuator.

Speed Sensor

T

Inlet Steam


governor

It regulates the speed of the Turbine

It operates a built in valve in the steam inlet line

It is either Mechanical or Hydraulic

In Mechanical type, the fly weights open out or close in,

which inturn opens or shuts the steam inlet vlave thereby

increasing or decreasing the speed respectively

In Hydraulic type, the oil pump pressure increases or

decreases raising or lowering the plunger or piston which

in turn actuates the steam valveGentech Design Center 13

e) Servo mechaniSm.

This mechanism works and an amplifier of governor This mechanism works and an amplifier of governor

signal for throttle valve activation.signal for throttle valve activation.

This consists of a pressure balanced pilot valve This consists of a pressure balanced pilot valve

controlling the supply of high pressure oil to the power controlling the supply of high pressure oil to the power

piston.piston.



F) oiL pumpS

Generally oil is containated in the reservoir which forms Generally oil is containated in the reservoir which forms

the turbine and gear box base plate.the turbine and gear box base plate.

Normally two oil pumps are available in turbines.Normally two oil pumps are available in turbines.

Main oil pumpMain oil pump

Auxiliary oil pumpAuxiliary oil pump


main oiL pump The main oil pump is driven by the low spoeed gear box / The main oil pump is driven by the low spoeed gear box /

extension.extension.

Main oil pump delivery pressure is approx.Main oil pump delivery pressure is approx.

5.0 to 6.0 kg/cm5.0 to 6.0 kg/cm22..

auxiLiary oiL pump

The auxiliary oil pump is driven by an electrical The auxiliary oil pump is driven by an electrical

motor/steam and is provided for use when starting and motor/steam and is provided for use when starting and

shutting down the turbine.shutting down the turbine.

Auxiliary oil pump delivery pressure is approx.Auxiliary oil pump delivery pressure is approx.

1.5 to 3.0 kg/cm1.5 to 3.0 kg/cm22.. Gentech Design Center 17

TypeS oF Turbine

A. Impulse Turbine

The steam pressure at the outlet side of the blade is equal to inlet side such a turbine is termed as impulse Turbine.

B. Reaction Turbine

The steam pressure at the outlet side of the blade is less than at inlet side of the blade.

A. Impulse Turbine

The steam pressure at the outlet side of the blade is equal to inlet side such a turbine is termed as impulse Turbine.

B. Reaction Turbine

The steam pressure at the outlet side of the blade is less than at inlet side of the blade.


diFFerence


(i) SimpLe impuLSe

Expansion of Steam takes place in one set of Nozzles. Hence called Impulse Turbines.

Employed for Small PowerGentech Design Center 20

(II) PRESSURE COMPOUNDED IMPULSE TURBINE

Number of Impulse Machines in series on the same shaft, allowing the exhaust of one turbine to enter the Nozzles of the succeeding turbine. Each simple Impulse Machine would be teamed as a ‘STAGE’. Gentech Design Center 21

(III) VELOCITY COMPOUNDED IMPULSE TURBINE (CURTIS TYPE)

This type comprises of a Nozzle of a wheel with two or more rows of moving blades. There are also guide blades, suitably arranged between the moving blades and set in reverse manner.Features: More efficient, better control of speed than simple impulse turbines. (Coppus Turbines) Gentech Design Center 22

STEaM TURBINES MaY BE CLaSSIfIED INTO ThE fOLLOwINg TYPES:

a) According to the method of steam expansion in the turbine. Impulse turbine Reaction Turbine Combination of impulse and reaction turbine.

b) According to the direction of flow of steam in the turbine Axial flow turbine Radial flow Turbine Mixed flow Turbin



c) According to the final delivery pressure (or) Exhaust condition of steam turbine.

Condensing Turbine Back Pressure Turbine. Extraction Turbine.



d) According to the number of stages of turbines.

Single stage turbine. Multi stage turbine.

d) According to the pressure of steam turbines.

Low pressure turbine. Medium pressure turbine. High pressure turbine.


SafETY DEVICES (MEChaNICaL DEVICES)

1. Over speed Trip

2. Master trip

3. LP Trip





DaNgER SIgNaLS

UNUSUaL VIBRaTION

NOISY BEaRINgS

aBNORMaLLY hOT BEaRINgS

OIL RINgS NOT TURNINg

DISCOLOURED OIL

LOw OIL PRESSURE

ExCESSIVE gLaND LEakagE

BROkEN LUBRICaTORS

gOVERNOR hUNTINgGentech Design Center 30

Starting the turbine


Protection SyStem

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)


StandardS

API 611General purpose steam turbines for refinery service (non-

critical)

API 612Special purpose steam turbine for refinery service (critical)


Parameter range


Inlet Pressure : ~ 4 ATA to 140 ATAInlet Temperature : ~ 1400 C to 5400 CExtraction Pressure : ~ 3 ATA to 64 ATAExhaust Pressure : ~ Condensing to 45 ATASpeeds : 3000 rpm to 25000 rpmPower : ~ 1 MW to ~ 100 MWDriven Machines : Generator Compressor Axial Turbo Blower Boiler Feed PumpInlet Temperature upto 5700 C for Special Application


trouble Shooting

• - Progressively increasing Vibration. - Steam Leakage - Seal DamageCauses * Journal/ Thrust Bearing failure

* Rotor Shaft Bent * Heavy fluctuations in inlet steam temperature Remedy * Check and replace Journal/ Thrust Bearing * Check & record readings of rotor * Proper operation of Boiler.

Labyrinth Rubbing


trouble Shooting

- Damage to Bearing - Vibration Causes * Oil Contamination. * Inlet temp of Oil is high. * Less oil supply .Remedy * Rectify Laby Glands. * Check oil cooler supply. * Check oil supply line is not chocked.

Bearing Failure


trouble ShootingGovernor - Hunting

- Cycle variations in speed above and below the normal set speed. Causes * Worn out thrust carrier * worn out needle roller bearing of rocker arm * worn out Gov. weights. - Remedy * Check & replace the bearings * Check & replace needle roller bearing of rocker arm * Check & replace Gov. weights.


Engineering

Steam turbine