Water and fire tube boilers

What is a boiler?
Boiler is an apparatus to produce steam. Thermal energy
released by combustion of fuel is used to make steam at
the desired temperature and pressure.
The steam produced is used for:
 (i) Producing mechanical work by expanding it in steam
engine or steam turbine.
 (ii) Heating the residential and industrial buildings
 (iii) Performing certain processes in the sugar mills,
chemical and textile industries.

Introduction
BURNER
WATER
SOURCE
BRINE
SOFTENERS
CHEMICAL FEED
FUEL
BLOW DOWN
SEPARATOR
VENT
VENTEXHAUST GAS
STEAM TO
PROCESS
STACK DEAERATOR
PUMPS
Figure: Schematic overview of a boiler room
BOILER
ECO-
NOMI-
ZER

Boiler properties
a). Safety: The boiler should be safe under the operating
conditions.
b). Accessibility: the various part of boiler should be
accessible for repair & maintenance.
c). Capacity: Should be capable of supplying Steam
according to the requirements.
d). Efficiency: Should be able to absorb a maximum amount
of heat produced due to burning of fuel in the furnace.
e). It should be simple in construction.
f). Its initial cost and maintenance cost is low.
g). It should be capable of quick starting and loading.

CLASSIFICATION OF BOILERS
 According to what flows in the TUBE
 1. Water tube.
 2. Fire tube.

Fire Tube Boilers
 The combustion gases pass inside boiler tubes, and heat is
transferred to water on the shell side.
• Relatively small steam capacities (12,000
kg/hour)
• Low to medium steam pressures (18 kg/cm2)
• Operates with oil, gas or solid fuels

Water Tube Boilers
 In this type of boiler water passes through the tubes while the
gases remain in the shell side, passing over the tube surfaces
• Used for high steam demand and pressure requirements
• Capacity range of 4,000 – 120,000 kg/hour
• Combustion efficiency enhanced by induced draft fans.
• Lower tolerance for water quality and needs water
treatment plant

Comparison between Fire-tube & water-tube boilers
S no. Particulars Fire tube boilers Water tube boilers
1. Mode of firing Internally fired Externally fired
2. Rate of steam production lower Higher
3. construction Difficult Simple
4. transportation Difficult Simple
5. Treatment of water Not so necessary More necessary
6. Operating pressure Limited to 16 bar Under high pressure as
100 bar
7. Floor area More floor area Less floor area
8. Shell diameter Large for same power Small same power
9. explosion Less More
10. Risk of bursting lesser More risk

BOILER MAIN COMPONENTS
 BOILER SHELL- The outer
cylindrical portion of a pressure vessel.
 BURNER - A device for the
introduction of fuel and air into a
furnace at the desired velocitie.The
burner is the principal device for the
firing of oil and/or gas.

 Mud Ring or Mud Drum
 A typically cylindrical shaped
space at the bottom of the water
space. Sediment, mud, and other
impurities gather there.
 FURNACE - An enclosed space
provided for the combustion of
fuel.

 SAFETY VALVE - A spring loaded
valve that automatically opens when
pressure attains the valve setting.
Used to prevent excessive pressure
from building up in a boiler.
 STEAM SEPARATOR - A device
for removing the entrained water from
steam.

BOILER MAIN
COMPONENTS
 STRAINER - A device, such as
a filter, to retain solid particles
allowing a liquid to pass.
 SIGHT GLASS- A glass tube
used on steam boilers to give a
visible indication of the boiler's
water level

BOILER MAIN
COMPONENTS
 DRAIN - A valve connection
at the lowest point for the
removal of all water from the
boiler.
 FEED PUMP - A pump that
supplies water to a boiler.

BOILER MAIN
COMPONENTS
 Ash Pit
 The ash pit is the space where
ashes accumulate under the
fire. The ashes fall through the
fire grate into a (often)
removable box.
 Grate
 The Grate is a series of bars or
narrow plates in the bottom of
the fire box. The ashes fall
through the grate into the ash
pit.

 Pressure Gauge. This
indicates the pressure of the
steam in the boiler.
 Fusible Plug . A fusible plug
operates as a safety valve when
dangerous temperatures,
rather than dangerous
pressures, are reached in a
closed vessel.

 Feed Check Valve. The
high pressure feed water is
supplied to the boiler
through this valve. This
valve opens towards the
boiler only and feeds the
water to the boiler.
 Steam Stop Valve.
 It regulates the flow of
steam supply outside.

Type of fire tube boiler
 Cochran Boiler
 It is a multi-tubular vertical fire tube
boiler having a number of horizontal
fire tubes. This is the modification of a
simple vertical boiler where the heating
surface has been increased by means of
a number of fire tubes.
 It is very compact and requires
minimum floor area.
 Any type of fuel can be used with this
boiler.
 Well suited for small capacity
requirements.

 Lancashire Boiler
 It is stationary fire tube, internally fired, horizontal,
natural circulation boiler. This is a widely used boiler
because of its good steaming quality and its ability to
burn coal of inferior quality.
 This boiler is set in brickwork forming external flue so
that the external part of the shell forms part of the heating
surface.

 LOCOMOTIVE
BOILER.
 Locomotive boiler is a
horizontal fire tube type
mobile boiler. The main
requirement of this boiler
is that it should produce
steam at a very high rate.
Therefore, this boiler
requires a large amount of
heating surface and large
grate area to burn coal at
a rapid rate.

Type of water tube boiler
 Simple vertical boiler
 A vertical boiler is a type of water-
tube boiler where the boiler barrel
is oriented vertically instead of the
more common horizontal
orientation. Vertical boilers were
used for a variety of steam-
powered vehicles and other mobile
machines, including early steam
locomotives.

 Stirling boiler
 The Stirling boiler is an early
form of water-tube boiler, used to
generate steam in large land-
based stationary plants.
 Stirling boilers are one of the
larger arrangements for a water-
tube boiler. They consist of a
large brick-built chamber with a
sinuous gas path through it,
passing over near-vertical water-
tubes that zigzag between
multiple steam drums and mud
drums.

 Babcock and Wilcox boiler
 The longitudinal drum boiler
is the generally accepted
standard of Babcock &
Wilcox construction. The
cross drum boiler, though
originally designed to meet
certain conditions of
headroom, has become
popular for numerous classes
of work where low headroom
is not a requirement which
must be met.

MERITS OF WATER TUBE BOILERS
OVERFIRE TUBE BOILERS
 1. Generation of steam is much quicker due to small
ratio of water content to steam content. This also helps
in reaching the steaming temperature in short time.
 2. Its evaporative capacity is larger and the steam
pressure range is also high-200 bar.
 3. Heating surfaces are more effective as the hot gases
travel at right angles to the direction of water flow.

 4. The combustion efficiency is higher because complete
combustion of fuel is possible as the combustion space is
much larger.
 5. The thermal stresses in the boiler parts are less as
different parts of the boiler remain at uniform temperature
due to quick circulation of water.
 6. The boiler can be easily transported and easily its
different parts can be separated.

 7. Damage due to the bursting of water tube is less
serious. Therefore, water tube boilers are sometimes
called safety boilers.
 8. All parts of the water tube boilers are easily accessible
for cleaning, inspecting and repairing.
 9. The water tube boiler's furnace area can be easily
altered to meet the fuel requirements.

Demerits :
 1. It is less suitable for impure and sedimentary water, as a
small deposit of scale may cause the overheating and
bursting of tube. Therefore, use of pure feed water is
essential.
 2. They require careful attention. The maintenance costs
are higher.
 3. Failure in feed water supply even for short period is
liable to make the boiler over-heated.

Water and fire tube boilers

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