Steam Boilers
UNIT-VI
Alpha Breathing- (2 mins)
Three steps for alpha breathing
1. Breathe-in (as much as possible)
2. Breathe-out (Slowly & Completely)
3. Hold (as long as possible)
(Repeat the three steps 8 times)
Evocation
Steam Boiler (or) Generator
• A boiler is a closed vessel which generates
steam by transforming heat produced by
burning of fuel to water.
• Heat energy is released by burning of fuel is
transferred to the water in the boiler.
• The boiler converts water into steam at the
required temperature and pressure.
Uses of steam
• Power generation
• Processing (like bleaching)
• Heating (residents and buildings in winter)
Primary requirements of
steam boiler or generator
• It should be capable of generating the max.
quantity of steam at required temp. and
pressure at low fuel consumption.
• The water must be safely contained.
• Consists of safe working condition as per IBR
(Indian Boiler Regulation).
Primary requirements of
steam boiler or generator
• All parts and components are easily accessible
for inspection and repair.
• The initial cost, installation cost and
maintenance cost of the boiler should be low.
• It should be a light in weight and should not
occupy more space.
Classification of boilers
• Horizontal, vertical and inclined
(according to the axis of cell)
• Fire tube and water tube
(according to flow of water and hot gases)
• Externally and internally fired
(according to the position of the furnace)
• Forced and natural circulation
(according to circulation of water)
• Stationary and portable
Classification of boilers
• Single tube and multi-tube
(according to the number of fire tubes)
• High and low pressure
(according to pressure of steam generated)
• Natural draught and forced draught
(according to movement of air circulation)
Simple vertical boiler
• It is an internally fired vertical low pressure fire tube
boiler.
• It is one of the fire tube boiler.
• Parts of the boiler
• Shell:
 It consist of steel plate.
 Cylindrical in form.
 Most of the shell is filled with water and remaining
portion is steam.
 Diameter – 1.5 m. height – 2 m
Simple vertical boiler
• Fire box
It consist of grate on which the fuel is burnt.
The ash from it falls into the ash pit.
• Central flue tube
 To carry the hot flue gases.
 As it passes through the tube the heat is
transferred onto the surrounding water.
• Fire hole
Charging door (through which the coal is fed)
Simple vertical boiler
• Pressure gauge
To indicate the steam pressure
• Water level indicator
To show the level of water inside the shell
• Steam safety valve
It act as safety valve when pressure inside the boiler exceeds it’s limit
• Chimney
The exhaust flue gases are let through it
• Steam stop valve
It like as a tap when the steam is required it is opened and closed after
use
• Blow off cock
The impurities like sand, sediments are removed.
Boiler mountings
• They are fitted on the boiler cell.
• The boiler mountings are used for the safety
of the boiler and for complete control of the
steam generation process.
• They are the integral part of the boiler.
Boiler mountings
•
•
•
•
•
Pressure gauge
Water level indicator
Steam safety valve
Steam stop valve
Fusible plug
Babcock and Wilcox boiler
• It is a water tube boiler.
• It is horizontal externally fired natural
circulation type stationary high pressure
boiler.
• Parts of the boiler
Boiler shell, water tubes, uptake and down take
header, Grate, Furnace, Baffles, Super heater,
Mud box, Damper, Inspection door.
Specifications of Babcock and Wilcox
water tube boiler
•
•
•
•
•
•
Diameter of drum – 1.5-2 m
Length – 6-10 m
Diameter of water tubes – 7.5-10.5 cm
Diameter of super heater tubes – 3.5-5.5 cm
Working pressure – 40 bar max.
Efficiency – 60-80 %
Working of Babcock and Wilcox water
tube boiler
•
•
•
•
Fuel
Coal is fed to the grate through the charging door
Flue gas circulation
From the combustion of fuel the flue gases are coming
out and move upwards.
• Baffles are arranged in a manner to deflect the hot flue
gases.
• So the gases are forced to move in the upward and
downward directions.
• The purpose of deflecting gases is to provide the
maximum heating of water tubes.
Working of Babcock and Wilcox water
tube boiler
• Water circulation
• The portion of the water in the tubes is heated which
are above the furnace.
• The heated water moves upward direction due to
decreased density and passes into the drum through
the up take header.
• The steam is separated from water and it is in upper
portion of the drum.
• The water enter into the tubes through the down take
header.
• This cycle is repeated. It is known as natural circulation.
Working of Babcock and Wilcox water
tube boiler
• Superheating
• The superheater is placed b/w drum and water
tubes.
• The steam that is collected it is passed through
the superheater and flows out of the boiler
through the steam stop valve.
• Mud box
• It is used to collect the impurities and sediments
in the water and it is removed by blow off cock.
Brain Activation: (2 mins)
Survey and Reading (15-18 mins)
Discussion: (9 mins)
Mindmap: (5 -7 mins)
Summary
Boiler systems are classified in a variety of ways. They can be classified
according to the end use, such as foe heating, power generation or process
requirements. Or they can be classified according to pressure, materials of
construction, size tube contents (for example, waterside or fireside), firing,
heat source or circulation.
Boilers are also distinguished by their method of fabrication. Accordingly, a
boiler can be pack aged or field erected. Sometimes boilers are classified by
their heat source. For example, they are often referred to as oil-fired, gasfired, coal-fired, or solid fuel –fired boilers.
Firetube boilers consist of a series of straight tubes that are housed inside a
water-filled outer shell. The tubes are arranged so that hot combustion gases
flow through the tubes.
Firetube boilers are subdivided into three groups. Horizontal return tubular
(HRT) boilers typically have horizontal, self-contained firetubes with a
separate combustion chamber.
Assessment: (5 min)
•
•
•
•
•
•
•
•
•
•
•
1. Which of the following enters the super heater of a boiler ?
(A) Cold water
(B) Hot water
(C) Wet steam
(D) Super-heated steam.
2. Which of the following is accessory of the boiler
(a) Air preheater
(b) Superheater
(c) Economiser
(d) All of the above
3. In water tube boiler
(a) Water passes through the tubes surrounded by flames and hot gases
(b) The flames and hot gases pass through the tubes surrounded by water
(c) Forced circulatin takes place
(d) None of these
4. Which of these statement is wrong
(a) Locomotive boiler is a fire tube boiler
(b) Water tube boilers are externally fired
(c) Cochran is a fire tube boiler
5. Boiler means any closed vessel exceeding ____capacity
(a) 22.7 litres
(b) 227 litres
(c) 0.227 litres
(d) 227 kg
Higher Order Questions
1. Explain the working principle the Wilcox and La-Mont boiler.