ME3K Micro Project – Thermal Engineering TEG (313310)-Prepare Report on Different Types of Boiler.

Part A

Title of micro Project :- Prepare Report and Chart on Different Types of Boiler.

Introduction :- A
boiler is an enclosed vessel that
provides a means for combustion and transfers heat to water
until it becomes hot water or
steam. The hot water or steam under pressure is
then usable for transferring the heat to a process. The
amount of heating surface of a boiler is expressed in square meters.

RESOURCE
REQUIRED

Loeffler Boiler

                                                             Part B

Title of Micro Project :– Prepare Report and Chart on Different Types of Boiler.

Introduction :- A boiler is an enclosed vessel that provides a means for combustion and transfers heat to water until it becomes hot water or steam. The hot water or steam under pressure is then usable

for transferring the heat to a process. The amount of heating surface of a boiler is expressed in square meters.

COURSES OUTCOME :-

1. Use relevantsteam boilers.

Types of Boilers

Different types of boilers are available in the market, which are manufactured by different manufacturers. The different types of boilers find their use in different applications. As the time has passed, more efficient types of boilers have replaced the old and inefficient

ones. This article elaborates on different types of boilers and the boiler classification. Boilers can be broadly classified as shell tube and water tube boilers.

Shell and tube boilers

Shell and tube boilers are also
referred to as fire tube or smoke tube boilers. Fire tube boilers; contain long steel tubes
through which the hot gasses from a furnace pass and around which the water to
be converted to steam circulates. Fire tube boilers, typically have a lower initial cost, are
more fuel efficient and easier to operate. Their capacities are up to 25tons/hr and 17.5 kg/
cm2.

Different types of fire tube boilers:

Cornish boiler

These are
the earliest form of high pressure fire tube boiler. These consist of long
horizontal cylinder with single large flue containing fire. Fuel is added in
the grate area where
it burn to produce hot gases. The hot gases transfer the heat to the water.

Water takes
heat and after some time it starts boiling to produce steam. Hot gases upon reaching at the end of the fire
tube, divided into two section and each move into the one of two side flue
which take them once again at the front section of the boiler where they are move into the bottom flue and
bottom flue take them toward the chimney.

Chimney throws these gases out
of the boiler into the atmosphere. Maximum heat

transfer is taken place at fire tube and shell section
then taken place at side flue and at last
at bottom flue.

For efficiency, the boiler was commonly encased beneath by a
brick-built chamber.

Lancashire boiler:

The
Lancashire boiler is similar to the Cornish, but has two large flues containing
the fires.
Pressure range of the boiler is about 0.7 MPa to 2 MPa and efficiency is 65 to 70%. Fuel in these boilers is added into the
grate which heats the gases.

Hot
gases enter the front section of the boiler and leave the boiler from back and then enter the bottom flue and start moving to front section of boiler. At front section hot gases leave the bottom flue and
enter in side flue and move again towards the back of the boiler and enter the main outlet. 85%
of heat is transferred when hot gases are in fire tube while 15% is transferred when they are
in bottom and side flue.

Locomotive
boiler

A locomotive boiler has three main components:

1.    
Double-walled
firebox;

2.    
Horizontal, cylindrical “boiler barrel”
containing a large number of small flue–tubes; and

3.    
Smokebox
with chimney, for the exhaust gases.

Fuel is
burned to produce the hot gases. Fuel is feed through fire hole. Hot gases are
diverted to fire
tube with the help of fire brick arch. Steam is collected in the steam drum
which is placed at the top of the shell.

The wet
steam goes through inlet headers of super heater and after passing through tubes, it returns to the outlet
header of super heater and is taken out for steam engine.

Locomotive-type
boilers are also used in traction engines, steam rollers, portable engines etc.

On the basis of construction these can be classified wet
back boilers and dry back boilers.

Reversal
Chamber:

This is the posterior portion of the combustion chamber through which the
flue gases travel from the first pass (furnace)
to the second-pass tubes

Wet Back Boilers:

In wet back
boilers as the name suggests the reversal chamber is completely surrounded
by water. The combustion reversal chamber is surrounded by water and therefore
the heat in the flue gases is optimally utilized. Radiation losses are reduced
as none of the parts of the combustion chamber are open to atmosphere
instead they are surrounded by water. That means fewer losses, and lesser fuel bills.
Most efficient modern boilers supplied are
wetback type.

Dry
Back Boilers:

The reversal
chamber in dry back boilers is not completely surrounded by water. The posterior
part is exposed to the atmosphere. This leads to the increased radiation losses,
as the radiant heat is lost to the atmosphere instead of going to the water as in
wet back boilers. Earlier generation boilers used to be dry back.Thus wet back
boilers ensure lesser radiation losses and hence save fuel.The layout of the
tubes involves the number of passes the tube will make to pass the heat from
the boiler furnace before being discharged. These can be two- pass and three pass
boiler.Depending upon the layout of tubes boilers can be two pass or three pass
boilers.

Two
pass boilers:

In two pass the
combustion gases travels two times in the boiler. Combustion gases should be
cooled before entering the reversal chamber. Excess temperature causes
overheating and cracking of the tube. The heat transfer rate is maximum at the first
pass, this rate decreases with the increasing passes.

Three pass boilers:

A three pass design provides three opportunities for heat driver the
stack temperature of 3 pass will be lower than that of 2 pass hope, of the
same design and operating pressure. Efficiency is more than two pass boiler.

Each pass in boiler should be designed with cross sectional area to
achieve optimal flue gas velocity, which
in turn maximizes heat transfer while also minimizing performance-robbing sooth
build up within the tubes.

No. Of pass Area of tube m2 Temperature OC Heat transfer 1st
11 1600 65%

2nd 43 400 25%

3rd 46 350 10%

Water tube boilers:

In water tube boilers, water and steam flow inside the tubes and the hot
gases flow over the outside surface. Modern high-capacity boilers are of water
tube type. The boiler circulation system is constructed of tubes, headers, and
drums joined in arrangement that provide water flow to generate steam. Water
tubes have high pressures and capacity than shell tube boilers. These boilers
can  be of single- or multiple-drum type.
These have higher efficiencies than fire tube boilers. Depending on layout
boilers can also be classified as:

1. Longitudinal drum boiler.

The
feedwater is feed in drum. The drum is placed above the
heat source. The cooler water goes to the inclined
tubes and the water is heating eventually in the hot tubes. As the water boils its density decreases and there is
circulation of hot water and steam.

Steam is separated from water in
steam drum and taken out. Longitudinal drum boilers
range from 2250 kg/h to 3600 kg/h.

 2. Cross drum boiler.