ATD UNIT3 PPT

7/28/2019 ATD UNIT3 PPT

1/41

STEAM BOILERS AND TURBINES

UNIT 3

Department of Mechanical Engineering 1/41 AppliedThermodynamics


2/41

Steam

Vapor of water.

It does not obey laws of perfect gases, until it is perfect dry.



3/41

Temp

(t)

Enthalpy (h)

Melting

Vaporization

Temperature Enthalpy diagram for formation of steam at constant pressure

Latent heat of iceSensible heat

of water Latent heat of steam Heat of super heat

Formation of steam


4/41

A

F D

C

E

B

LkG

(Critical Point)

N M

S.H L.H of vaporisation H.S

p2

p1

p

Water region

Superheated Region

Temperature Vs Total Heat Graph in steam formation



5/41

Wet steam: moisture or water particles Dry steam: does not contain any water particles

Superheated steam: dry steam is further heated at constantpressure it is said to be superheated steam

Dryness fraction (quality of wet steam): Mass of actual dry steam/ mass of same quantity of wet steam

X= mg / (mg + mf)

Enthalpy = S.H. + L.H

For wet steam h = hf

+ x hfg

For dry steam h = hf+ hfg

For super heated steam h = hf+ hfg + Cp (tsupt)


Important terms for steam


6/41

Entropy For wet steam s = sf+ x sfg

For dry steam s = sf+ sfg

For super heated steam s = sf+ sfg + Cp (tsupt)

Specific volume

For wet steam v = x vg

For dry steam v = vg

For super heated steam vsup

/ Tsup

= vg

/ T

Important terms for steam



7/41

Pressurized steam is accelerated through a nozzle and then

directed (almost) tangentially onto blades attached to a rotatingwheel.

Steam Turbines



8/41

By details of stage design Impulse

Reaction

By direction of steam flow

Axial flow Radial flow

Tangential

By no of stages

Single Multi-stage

Classifications of Turbines



9/41

Advantages

Can give very high powers

Has good steam economy

Is very reliable

Has long life

Is small in size for its power

Disadvantages

Is non reversible Has poor starting torque

Features of Steam Turbines



10/41

The action of the jet of steam, impinging on the blades, is said

to be an impulse and the rotation of the rotor is due to the

impulse force of the steam jets

steam passes through stationary converging nozzles reduce its pressure (and its temperature) and increase its

velocity

converting its "heat energy" (enthalpy) into kinetic energy

Runs by the impulse of steam.

Impulse Turbines



11/41

Impulse Turbines Blades



12/41

Impulse Turbines Blades



13/41

The steam enters the wheel under pressure and flows over the

blades.

The steam while gliding propels the blades and make them tomove

So the runner is rotated by the reactive forces of the steam jet.

Reaction Turbines



14/41

Reaction Turbines Blades



15/41

High pr and high temp Boiler pr to condenser pr (1 to 125 bar) pr drop carried out

only in one stage, so velocity of entering steam is extremely

high

To control the extreme entering velocity of steam jetcompounding is used.

Types:

Velocity compounding

Pressure compounding VelocityPressure compounding

Compounding of Impulse Turbines



16/41

Fixed nozzle and Moving Blades

In nozzle: Pressure Decrease; Velocity Increase

Moving blades: Pressure constant; Velocity decrease

Total pressure drop occurs in different fixed nozzle, not in

single nozzle

Pressure compounding of Impulse Turbines



17/41

Pressure Compounding



18/41

Fixed nozzle, Moving Blades and Guiding Blade



Guiding blades: Pressure constant; Velocity slightly decrease

Total velocity drop occurs in two or more number of movingand guiding blades.

Velocity compounding of Impulse Turbines



19/41

Velocity Compounding



20/41

Fixed nozzle, Moving Blades and Guiding Blade



Guiding blades: Pressure constant; Velocity slightlydecrease

In this method large amount of pressure drop is allowed,so less number of stage is enough

Pressure Velocity compounding



21/41

Pressure Velocity Compounding



22/41

In impulse turbines The entire pressure drop takes place in fixed nozzles,

The pressure across the moving blades remains constant.

The velocity decreases through the moving blades and remainsfairly constant in the fixed blades.

In reaction turbines

Specially shaped fixed and moving blades replace the nozzles

The drop in pressure takes place equally across both fixed andmoving blades,

Falling progressively throughout the turbine.

Absolute velocity decreases in the moving blades, butincreases in the fixed blades.

Key difference between Impulse and Reaction Turbines



23/41

1. The steam jet impinges the

turbine blades

2. Steam may or may not be

admitted over the whole

circumference

3. Steam pressure constant in

moving blade

4. Blades are symmetrical

5. No of stages required is less

1. Steam glides over the moving

vanes with pressure and K.E

2. The steam must be admitted

over the whole circumference

3. Steam pressure reducing inmoving blade

4. Blades are asymmetrical

5. No of stages required is more

Difference Between Impulse and Reaction Turbines



24/41

Locomotive Boiler



25/41

Babcock and Wilcox Boiler



26/41

Lamont Boiler



27/41

Benson Boiler



28/41

Mountings

Fittings mounted on the boiler for its proper and safe functioning.

Accessories

The devices which are used as integral part of a boiler and help in

running efficiently.

Boiler Mounting and Accessories



29/41

Measure the pressure of

steam inside the boiler

Placed in front of boiler

Bourdon pressure gauge

Pressure Gauge



30/41

To indicate the level of

water inside the boiler

Placed in front of boiler

Water Level Indicator



31/41

To prevent the explosions

due to excessive internal

pressure

Two safety valve

Placed on boiler

It is used to maintain

constant safe pressure

inside the boiler

Lever Safety Valve



32/41

Advantage is readily

tempered.

Disadvantage is heavyload which these valves

carry

Dead Weight Safety Valve


S i L d d S f V l


33/41

Loaded with springinstead of weights

Spring Loaded Safety Valve


St St V l


34/41

It is the largest valve

To control the flow of

steam from the boiler to

the main steam pipe

To shut off the steam

completely when required

Steam Stop Valve


Bl Off C k


35/41

Placed at bottom of boiler

To empty the boiler when

required

To discharge the mud,

scale or sediments which

are accumulated at the

bottom of the boiler

Blow Off Cock


F d Ch k V l


36/41

Non return valve

It is located slightly below

the normal water level ofthe boiler

To regulate the supply of

water


Feed Check Valve

F ibl Pl
http://images.google.co.in/imgres?imgurl=http://www.hnsa.org/doc/merchant/engineering/img/pg12a.jpg&imgrefurl=http://www.hnsa.org/doc/merchant/engineering/index.htm&usg=__zQI_ITo6iRpIiS74kGMNoKL1DI4=&h=412&w=300&sz=24&hl=en&start=23&um=1&itbs=1&tbnid=ZNkWA4W5ju94jM:&tbnh=125&tbnw=91&prev=/images%3Fq%3Dfeed%2Bcheck%2Bvalve%2Bin%2Bboiler%26start%3D20%26um%3D1%26hl%3Den%26lr%3D%26safe%3Dactive%26sa%3DN%26gbv%3D2%26imgtbs%3Df%26ndsp%3D20%26tbs%3Disch:1


37/41

It is fitted to the crown of

the furnace

To put off the fire whenthe water level falls to an

unsafe level

It avoids explosion by over

heating of boiler

Fusible Plug



38/41

Accessories


S H t


39/41

To increase the

temperature of saturated

steam without raising itspressure.

Placed in the path of hot

flue gas from the furnace.

Super Heater


E i


40/41

To heat the feed water

Utilizing the exhaust flue

gas

Before leaving to chimney

Green economizer

15 to 20 % of coal saving

Prevent scale formation

Scraper

Economizer


Ai P h t


41/41

To recover heat from

exhaust gas

Placed between the

economizer and chimney

Air temperature is raised

Increase the evaporative

capacity

Less soot

Air Preheater

f h l E / l d h d

ATD UNIT3 PPT

Documents

Transcript of ATD UNIT3 PPT