Different features of Boiler

1.0.Introduction:
A boiler is a closed vessel in which fluid (generally water) is
heated. The fluid does not necessarily boil. The heated or
vaporized fluid exits the boiler for use in various processes or
heating applications,[1][2] including water heating, central
heating, boiler-based power generation, cooking, and
sanitation.

A moveable (mobile) boiler.

Its used to create steam by applying heat energy to water.

Although the definitions are somewhat flexible, it can be said
that older steam generators were commonly termed boilers
and worked at low to medium pressure (7–2,000 kPa or 1–290
psi) but, at pressures above this, it is more usual to speak of a
steam generator.
2.0.Main parts of a Boiler:
Main Components of Boiler
Burner – the burner is the area where the air mixes with your
fuel source and combusts.
Combustion chamber/firebox – this is the chamber where the
combustion from the burner heats the heat exchanger; this
chamber can reach temperatures of several hundred degrees.
Heat exchanger – the heat exchanger allows the heat from
the combustion chamber to heat the water in the boiler’s tank.
Aquastats – these components sense the temperature of the
water in your boiler and tell the burner when to start and stop.
Expansion tank – the expansion tank is a small tank off the main
boiler that helps protect your system from
excessive pressure.
Backflow valve – a backflow valve is a safety device that allows
water to flow in a single direction only.
Circulator pump – a circulator pump is used with boilers that
use hot water to heat; the circulator pump pushes the hot
water through your system, allowing it to circulate to the
various outlets.
Supply lines – supply lines are the pipes that deliver the heated
water or steam to the distribution points.
Return lines – when the water cools, or the steam cools and
changes states back to water, the return lines bring this water
back to the boiler
3.0.Classification of Boiler:
A boiler may be classified as follows:
(i) Fire tube and water tube boilers
(ii) High-, medium-, and low-pressure boilers
(iii) Natural and forced circulation boilers
(iv) Single tube and multi tube boilers
(v) Stationary and portable boiler
(vi) Coal-, oil-, and gas-fired boilers
(vii) Externally fired and internally fired boilers
4.0.Boiler mountings and accessories :
Boiler mountings
:Boiler mountings are those mechanical appliances which are
considered essential for operating a boiler smoothly and safely
which are usually mounted on the surface of a boiler.
The followings are the important mountings of a boiler:
Water level indicator
Pressure gauge
Safety valve
Fusible plug
Steam stop valve
Blowoff valve or blowdown valve
Feed check valve
Water level indicator:
The water level indicator located in front of the boiler in such a
position that the level of water can easily be seen by the
attended.
There are two indicators:

A water level indicator consists of a metal and a strong glass

tube with marking. The upper and lower ends of these tubes
are connected to two gunmetal hollow pipes.
The upper pipe has a steam valve and the lower pipe has a
water valve which is bolted to the boiler plated by two flanges.
The upper pipe is opened to the steam and the lower pipe is
open to the water with the help of steam and water valves,
respectively.
In case of glass gauge breaks accidentally, the water and steam
simultaneously rush out through the gunmetal pipe and they
are carried away by water and steam and passages are closed.
The water and steam valves are then closed and the glass
gauge is replaced.
Pressure gauge:
A pressure gauge is fitted in front of a boiler in such a position
that the operated can conveniently read it. It reads the
pressure of steam in the boiler and is connected to the steam
space by a siphon tube.
Safety valve:
The safety valve is a relief valve that prevents the boiler
pressure from raising over its normal working pressure by
automatically opening when the boiler pressure exceeds the
normal working pressure, thus allowing excess steam to escape
into the atmosphere until the pressure comes down on its
normal value.
Thus, a safety valve ensures safety to a boiler from being
damaged due to excessive steam pressure.
It also ensures safety to a pipe or vessel containing water under
high pressure.
There are generally four types of safety valve.
These are:
Lever-type safety valve
Deadweight type of safety valve
Spring-loaded safety valve
High steam and low water safety valve
Fusible plug:
The function of a fusible plug is to ensure safety to the boiler
from being damaged by overheating due to water level falling
very low in the boil
Steam stop valve:
The function of a steam stop valve (this is called main stop
valve) is to control the flow of steam from within the boiler and
to stop it completely.
Blow-off valve or blow-down valve:
The function of a blow–off valve is to remove periodically the
sediments deposited at the bottom of the boiler while the
boiler is in operation and to empty the boiler while it is to be
cleaned or inspected. When the blow-off valve is opened the
water which is under the pressure of steam, rushes out with
tremendous velocity thus crying out the sediments along with
it.
Feed check valve:
The function of a feed check valve is to control the flow of
water from the feed pump to the boiler and to prevent the
backflow of water from the boiler to the pump when the pump
pressure is less than the boiler pressure or when the feed pump
ceases to work
Boiler accessories:
What are the boiler Accessories? Boiler accessories are those
appliances and plants which are installed along with a boiler to
improve the operating condition and overall efficiency of the
boiler plant.
There are several boiler accessories, and those are:
Economizer
Superheater
Steam separator
Steam trap
Feed pump
Injector
Let’s discuss them all.
Economizer:
The economizer is a plant in which the feed water is preheated
before it enters into a boiler, the heat is taken from the waste
flue gases of the boiler
Advantages:
Saving of fuel
The increase in the evaporative capacity of the boiler.
The long life of the boiler.
Superheater:
It is a heat exchanger in which products of the heat of
combustion is utilized to dry the wet steam and to make
superheated by increasing its temperature.
During superheating of the steam, pressure remains constant
and its volume and temperature increase. A superheater
consists of a set of small diameter U tube in which steam flows
and takes up the heat from hot flue gases.
Advantages:
There is a saving in fuel consumption.
The overall efficiency is increased.
Steam separator:
Saturated steam obtained from all types of industrial boilers
contains some water particles which decries the economy and
efficiency of steam engines and steam turbines. For this, a
steam separator is fitted before the steam engine or steam
turbine to separated water particles from steam.
Steam trap:
The function of a steam trap is automatically to drain away or
return to the boiler, the water collected in the steam pipe or
steam jacket due to partial condensation of steam without
allowing steam escape.

Feed pump:
Feed pump delivers feed water at a pressure higher than that in
the boiler.

There are two types of feed pumps.

1.Reciprocating feed pump

2.Rotary feed pump
Reciprocating feed pump:
These are positive displacement type pumps. The most popular
types of reciprocating feed pump used in a boiler is a duplex
feed pump. It consists of a steam engine and a water pump side
by side.
Rotary feed pump:
It is a high-speed centrifugal pump and is used to deliver a large
quantity of water into the boiler. It consists of impeller and
casing.
Injector:
An injector is a simple device used to supply feed water into the
boiler. It has no moving parts and water is supplied into the
boiler by the action of steam flowing through nozzles. This type
of feed pump is used in locomotives.
5.0.Difference between boiler mountings and accessories:
Mountings. Accessories
1. Boiler mounting is an essential apparatus without which a
boiler cannot be operated. 1. Boiler accessory is not an
essential apparatus.
2. Boiler mountings are mounted on the boiler. 2. Boiler
accessories are not generally mounted on the boiler but
installed within or near the boiler.
3. Boiler mounting occupies less floor space.3. Boiler accessory
occupies comparatively greater floor space.
6.0.Drawing of the model Diagram of a water tube Boiler:
7.0.Working Principle of the water tube boiler: