International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
doi: 10.14355/ijace.2014.0303.02
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Boiler and Its Tangential Fuel Firing System
Sharukh khan & Shahabaz Khan
Electronics & Communication Engineering & Electrical Engineering, SIND - JNTUH
SIND- JNTUH , Andhra Pradesh, INDIA
Sharukhan472@gmail.com, shahabaz100@gmail.com
Abstract
Introduction
Boiler can also be called as “the Burner”.The main Function
of the Boiler is to Burn the Fuel and Make Combustion
possible. In this project we are going to study how coal is
pulverized and burnt in order to gain more heat.
A thermal power station works on the basic principle
that heat liberated by burning fuel is converted into
mechanical work by means of a suitable working fluid.
The mechanical work is converted into electrical
energy by means Of generator. In a steam power
station, heat is realized by burning fuel, this heat is
taken by water, which works as the working fuel.
Water is converted into steam as it receives heat in the
boiler. The steam then expands in turbine producing
mechanical work, which is then converted into
electrical energy through a generator. The exhaust
steam from the turbine is then condensed in the
condenser and the condensate is there after pumped to
the boiler where it again receives heat and the cycle is
repeated. The basic theoretical working cycle is of a
steam power plant is ‘THE RANKINE CYCLE’. The
modern steam power plant uses ‘MODIFIED
RANKINE CYCLE’, which includes reheating,
superheating and regenerative feed water heating.
Most coal fired power station boilers use pulverized coal.
This technology is well developed, and there are thousands
of units around the world, accounting for well over 90% of
coal fired capacity. The coal is pulverized to a fine powder,
so that less than 2% is +300 micro meter (μm) and 70-75 % is
below 75 microns, for a bituminous coal. This system has
many advantages such as ability to fire varying quality of
coal, quick responses to changes in load, use of high pre-heat
air temperatures etc. One of the most popular systems for
firing pulverized coal is the tangential firing using four
burners corner to corner to create a fireball at the centre of
the furnace.
Keywords
Rankine Cycle; Condenser; Dearator; Economiser; Reheater;
Recipitator & Pulveriser
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
Water tube type
Horizontal Straight tube
Bent tube
Natural Circulation
Positive Circulation
Shell type
Cast Iron Boilers
Special Design Boilers
Nuclear Reactors
Principle of Power Generation at Coal
Based Power Plant
The main function of oil and coal burning system is to
convert chemical energy into heat energy, which is
utilized by the components of the boiler to convert
water into the steam, which drives the turbine. The
combustion element of fuel consists of carbon,
hydrogen and small amount of sulphur. The exhaust
gases released after combustion contains CO2, SO2
and CO, etc. When the coal is burnt with oxygen
following reaction takes place and large amount of
heat is released.
𝐶𝐶 + 𝑂𝑂2 → 𝐶𝐶𝑂𝑂2
𝑆𝑆 + 𝑂𝑂2 → 𝑆𝑆𝑂𝑂2
𝐶𝐶 + 𝑂𝑂2 → 2𝐶𝐶𝐶𝐶
The average composition of air is
79% nitrogen and 21% oxygen by volume
77% nitrogen and 23% oxygen by weight
 During combustion process nitrogen does not
burn but passes through the chimney.
 The amount of air required to burn any fuel can be
calculated if the amount of the elements present in
the fuel are known.
 The amount of air to burn is known as theoretical
air. If this quantity is not sufficient for complete
combustion process then extra amount of air is
supplied, known as excess air. In combustion
process, turbulence, time, temperature and
combustion efficiency are the important
parameters to be considered.
 The steam generator is a natural circulation, single
drum type, corner fired, and natural draft unit of
water tube type.
 In water tube boiler, boiler feed water flows
through the tubes and enters the boiler drum. The
circulated water is heated by the combustion of
gases and converted into steam at the vapor space
in the drum.
 These boilers are selected when the steam
demands as well as the steam pressure
requirements are high as in the case of process
cum power boilers. The steam generating boiler is
designed for following conditions.
1.
2.
3.
4.
5.
The features of water tube boilers are:
 Forced, induced and balanced draft provisions
help to improve combustion efficiency.
 Less tolerance for water quality calls for water
treatment plant.
 The maximum combustion efficiency depends on
1.
2.
3.
Design of boiler
Fuel used
Skill in obtaining combustion within the
minimum amount of excess air.
Boiler (Steam Generator)
Boiler or the steam generator is the main part in the
power generation process. Boiler acts as a medium in
which the water is converted into the steam by using
the heat released in the process of combustion of coal
in the presence of oxygen.
Categorization of Boilers
Boilers are generally categorized as follows:
Steel boilers
Fire Tube type
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Main steam flow
670000 kg/hr.
Main steam pressure
157 kg/𝑐𝑐𝑐𝑐2
Main steam temperature
540 ºC
Reheat steam flow
580000 kg/hr.
Reheat steam temperature 540 ºC
 Higher thermal efficiency levels are possible.
There are many mountings to the boiler, which are
compulsory for the safe run of the boiler. Also, there
are accessories, which increase the efficiency of the
boile
Arrangement of Main Boiler
The illustration given in figure below shows a
symbolic arrangement of various accessories of a
Boiler. These accessories include
1.
2.
3.
4.
5.
Economizer
Boiler drum
Down Comers
Water walls
Water wall platen (used for Low Pressure Boilers)
International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
6.
7.
8.
9.
10.
11.
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Supporting Structures:
Primary super heater
Platen super heater
Final super heater
Reheater
Burner
Igniters
Boilers supporting structure consists of a systematic
arrangement of columns stiffened with horizontal
beams and vertical diagonal bracings and comprise of
Low carbon steel material. It is composed of 18 main
columns and 12 auxiliary columns. The main columns
support the main boiler components viz. drum, water
wall, Membrane, panels, superheaters, Reheater,
economizer’s, air preheater, burners and galleries at
various levels. The auxiliary columns, supports the
boiler platforms and other ducts coming in that
region.The total weight of supporting structures is
about 970 M.T.
Galleries and Stairways:
Galleries and stairways around the combustion and
heat recovery areas are provided for proper approach
to the boiler. Stairways on both the side of boiler are
provided. All the floors are covered with floor gratings
of required depth for walkway and are tig welded to
the structure. The total weight of Galleries and
stairway are 900 M.T.
Furnace
FIG. SHOWING BOILER BLOCK DIAGRAM
Boiler Structural:
The boiler structural is divided into two parts.
•
•
Supporting Structure
Galleries and stair ways
A boiler furnace is that space under or adjacent to a
boiler in which fuel is burned and from which the
combustion products pass into the boiler proper. It
provides a chamber in which the combustion reaction
can be isolated and confined so that the reaction
remains a controlled force. In addition it provides
support or enclosurefor the firing equipment
FIG. SHOWING FURNACE INTERNAL STRUCTUR
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
Boiler Drum
The function of steam drum is to separate the water
from the steam generated in the furnace walls and to
reduce the dissolved solid contents of the steam to
below the prescribed limit of 1 ppm. The drum is
located on the upper front of boiler.
of radiant parallel flow type. The third stage
superheater pendant spaced is of convection parallel
flow type. The outlet temperature and pressure of the
steam coming out from the superheater are 540°C and
157 Kg/Cm2 respectively for H.P.units.
Economiser
The purpose of economizer is to preheat the boiler
feed water before it is introduced into the steam drum
by recovering heat from the flue gases leaving the
boiler. The Economiser is located in the boiler rear gas
pass below the rear horizontal superheater. The
economizer is continuous unpinned loop type and
water flows in upward direction and gas in the
downward direction.
FIG. SHOWING SUPER HEATER OF BOILER
Reheater
The function of Reheater is to reheat the steam coming
out from high pressure turbine to a temperature of
540°C. The Reheater is composed of two sections, the
front pendant section and the rear pendant section.
The rear pendant section is located above the furnace
arc and the rear water wall and front pendant section
is located between the rear water hanger tubes and the
superheater platen section.
FIG. SHOWING ECONOMIZER INTERNAL TUBES
Super Heater
There are three stages of superheater besides the side
walls and extended sidewalls. The first stage consists
of horizontal superheater of convection mixed flow
type with upper and lower banks located above
economizer assembly in the rear pass. The upper bank
terminates into hanger tubes, which are connected to
outlet header of the first stage superheater. The second
stage superheater consists of pendant platen which is
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FIG. SHOWING REHEATER WITH 600 NIPPLES
Burners
There are total twenty four pulverized coal burners for
corner fired C.E. type boilers and twelve oil burners
provided each in between two pulverized fuel burner.
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The pulverized coal burners are arranged in such a
way that six mills
boiler. The atomizing air for igniters is taken from
plant air compressors at 7 Kg/cm2 (gauge).
Supply the coal to the burners at 4 corners, of the
furnace. All the nozzles of the burners are inter
The burners are located at three elevations. Each
elevation has four oil burners and igniters. These
elevations are normally known as AB elevation, CD
elevation and EF elevation. Igniters are used for
lighting the main oil gun. There are two igniter air
fans supply air for combustion of igniter oil. Mainly
two types of igniters are used.
Linked and can be tilted as a single unit from +30° to 30°.The oil burners are fed with heavy fuel oil till
boiler load reaches to about 25%.
1.
Eddy Plate Igniter
2.
High Energy Arc Type Ignite
FIG. SHOWING BURNER OF A BOILER
Igniters
There are twelve side eddy plate oil/H.E.A igniters per
FIG. SHOWING EDDY PLATE IGNITER
Boiler Auxilliaries
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
Coal Bunker
Wind Box
These are in process storage silos used for storing
crushed coal from the coal handling system. Generally,
these are made up of welded steel plates. There are
totally eight bunkers, four on each side of the boiler.
Normally, there are six such bunkers supplying coal to
the corresponding mills. These are located on top of
the mills so as to aid in gravity feeding of coal.
These act as distributing media for supplying
secondary/excess air to the furnace for combustion.
These are generally located on the left and right sides
of the furnace while facing the chimney.
Coal Feeders
Each mill is provided with a drag link
chain/rotary/gravimetric feeder to transport raw coal
from the bunker to the inlet chute, leading to mill at a
desired rate.
Mills
There are six mill (25% capacity each), for every 200
MW unit, located adjacent to the furnace at '0' M level.
These mills pulverize coal to the desired fineness to be
fed to the furnace for combustion.
P.A. Fan
The primary air fans (2 per unit - 50% capacity each)
are designed for handling atmospheric air up to a
temperature of 50 ºC. These fans are located at ‘0’M
level near the boiler.
Air Pre-heater
Air pre-heater transfers heat from flue gases to cold
primary and/ or secondary air by means of rotating
heating surface elements. Beneath these regenerative
type air pre-heaters, there exists a steam coil air preheater.
Electrostatic Precipitator
These are generally two plate type located between
boiler and the chimney. The precipitator is arranged
for horizontal gas flow and is constructed with welded
steel casings.
ID Fans
There are two induced draft fans per boiler located
between the Electrostatic precipitator and the chimney.
These fans are used for sucking flue gas from furnace.
Chimney
These are tall RCC structures with single/multiple
flues (one flue per 200 MW Unit). The heights of these
chimneys vary depending on the location
considerations; anywhere between 150 m. to 220 m.
Seal Air Fan
These are used for supplying seal air to the mills to
prevent ingress of coal dust into gear box lubrication
oil. There are two fans per boiler for 200MW units.
Soot Blowers
These are located in the secondary pass of the furnace
at a height of around ‘16’ M level. Each 200 MW unit is
provided with two such air pre-heaters.
Burners
As evident from the name itself, these are used for
burning pulverized coal or oil. Every unit has a set of
such burners located at different elevations of the
furnace.
F.D.Fan
The forced draft fans (2 per unit - 50% capacity each)
are designed for handling secondary air for the boiler.
These fans are located at '0' M level near the PA Fan.
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FIG. SHOWING CORNER OF A TANGENTIAL BURNER
Following three types of soot blowers, in requisite
numbers, are provided:
International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
i.
ii.
iii.
Long retractable soot blowers
Wall blower
Air heater blower Superheated steam is tapped
from super heater for the purpose of soot
blowing.
The pressure is reduced to 31 Kg/cm2 at 330 ºC by
means of pressure reducing valve. The soot blowers
are used for efficient on-load cleaning of furnace,
super heaters, reheaters and regenerative air heaters.
Fuel Firing System
Most coal fired power station boilers use pulverized
coal, and many of the larger industrial water tube
boilers also use this pulverized fuel. This technology is
well developed, and there are thousands of units
around the world, accounting for well over 90% of
coal fired capacity.
 The coal is pulverized to a fine powder, so that less
than 2% is +300 micro meter (μm) and 70-75 % is
below 75 microns, for a bituminous coal. It should
be noted that too fine a powder is wasteful of
grinding mill power. On the other hand, too coarse
a powder does not burn completely in the
combustion chamber and results in higher unburnt
losses.
 The pulverized coal is blown with part of the
combustion.
 Air into the secondary boiler plant through 2 series
of burner nozzles. Secondary and tertiary air may
also be added. Combustion takes place at
temperatures from 1300-1700ºC, depending largely
on the coal grade. Particle residence time in the
boiler is typically ₐ to 5 seconds, and the particles
must be small enough for complete combustion to
have taken place during this time.This system has
many advantages such as ability to fire varying
quality of coal, quick responses to changes in load,
use of high pre-heat air temperatures etc.
 One
of the most popular systems for firing
pulverized coal is the tangential firing using four
burners corner to corner to create a fireball at the
center of the furnace.
Fuels
There are two types of fuels which play a vital role in
fuel firing system. They are:
1.
2.
Coal
Oil
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Coal
Fuel (coal) is fed from mines to the boiler through the
fuel feeding plant commonly known as “Coal
handling plant”. Selection of proper methods of coal
supply from the mines to the power station depends
upon the system capacity in the tons/hour, location of
available outsides storage and overhead coal bunkers.
The unloading will take place by “Merry Go Round”
system in which loading and unloading will take place
within 12-20 minutes. Coal is crushed to the sizes of
25mm in the crusher house before it is fed to the
bunkers of individual units. The coal from CHP is
transferred to the bunkers through the conveyer belts
via turning points. The storage capacity of bunkers in
terms of time is 14 hours.
The coal from the bunkers enters the mills through the
coal feeders by gravity action. The quantity of coal
reaching the coal mill is controlled by feeders by
altering the speed of DC motors as per the
requirements of the unit.
Coal Bunker
These are in process storage silos used for storing
crushed coal from the coal handling system. Generally,
these are made up of welded steel plates. Normally,
there are six such bunkers supplying coal of the
corresponding mills. These are located on top of the
mills so as to aid in gravity feeding of coal.
Coal Feeders
In most of the power stations the types of feeders used
for transporting coal from Raw Coal bunker to the
mills are:
1.
2.
Volumetric feeders
Gravimetric type feeders
Mills
 Pulverised fuel firing is a method whereby the
crushed coal, generally reduced to fineness such
that 70-80% passes through a 200 mesh sieve, is
carried forward by air through pipes directly to
burners or storage bins from where it is passed to
burners.
 When discharged into combustion chamber, the
mixture of air and coal ignites and burns in
suspension.
 The economic motives for the introduction and
development of pulverised fuel firing are:
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
i.
Efficient utilization of cheaper low grade coals.
c) Low sulphur heavy stock (LSHS).
ii.
Flexibility in firing with ability to meet
fluctuating loads.
iii.
Elimination of banking losses.
iv.
Better reaction to automatic control.
v.
Ability to use high combustion air temperature;
increasing the overall efficiency of boiler.
The boiler is equipped with equipment for heavy oil
firing at elevation AB, CD and EF. Heavy oil guns are
used for stabilizing flame at low load carrying. Warm
up oil guns are used for cold boiler warm up during
cold start up and igniter are used for start-up and oil
flame stabilizing.
vi.
High availability.
 The only disadvantage is that the initial cost of
equipment for preparation of pulverised coal will
be high.
 This system requires maximum total output of the
oil burners is 30% of the boiler MCR heat input
with HFO and 7.5 % of the boiler MCR heat input
with LFO. This corresponds to synchronisation
needs before firing coal burners.
 For the preparation of fuel oil, pumping the oil and
heating are the major preparatory functions to
remove any dust, dirt, sediment, sludge, etc.
 Fuel oil atomisation is the process of spraying the
fuel oil into fine mist for better mixing of fuel with
combustion air. By passing through the spray
nozzles of the oil gun, the pressure
 Energy of the oil converts into fine particles.
Fuel Data
Oils
A coal fired unit incorporates oil burners to a firing
capacity of 30% of boilers load for following reasons:
a) To provide necessary ignition energy to light
off coal burner.
b) To stabilise the coal flame at low boiler/burner
loads.
c) As a safe start-up fuel and for controlled heat
input during light off.
Firing Systems:
This can be broadly classified into direct firing system
and indirect firing or intermediate bunker system.
Both the systems can use any type of mill. Either hot
gas or air can be used for drying and transporting the
coal.
The types of oil used in the oil burners are:
Direct Firing System
a) Light Diesel Oil
b) Heavy fuel oil
 In this type of firing system, coal is fed to the mill
at controlled quantity. Hot air whose temperature
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
can be controlled with the help of cold air is
permitted to flow through the mill. The air dries
the coal and picks up the milled product and flows
through the classifier where higher size particle is
rejected back to the mill.
 The fine coal is carried by the air through the coal
burner to the combustion chamber. The flow
through the system is carried out by primary air
fan or by exhauster. In case of hammer mills forced
draft itself can do the purpose of primary air fan.
 This system is simple involving minimum
equipment hence minimum initial cost and
maintenance cost. As there is no fine coal storage
the mill load is varied according to the boiler load.
Hence part load operation of mill is essential and
this means increase in power consumption and
maintenance per tonne of coal.
 Mill outage will result in reduction of boiler
output if spare mills are not provided or available.
This is best suited to use with high speed and
medium speed mills as the mill power
consumption varies in direct proportion to the mill
load. Tube ball mills with this system is also used
but to a limited extent.
Indirect Firing System
 In this system, mills are operated independent of
boiler loading and pulverised coal is stored in the
intermediate bunker.
 From the bunker it is taken to combustion chamber
with the help of primary air fan. Boiler loading is
controlled by the amount of pulverised fuel fed to
boiler. Hot air or gas is used for drying and
transporting.
 Cyclone type separators are used to separate the
fine coal from coal, air/gas mixture for storing in
fine coal bunker. As fine coal dust cannot be
completely removed by cyclone type separators, a
certain portion of very fine particle is carried along
by air/vapour. This necessitates admissions of
vapour/air into the combustion chamber to utilise
the heating value of fine coal dust carried along
with vapour/air. This can be done by providing
separate vapour burners or the air can be used as
primary air for carrying the fine coal.
 This system using gas as drying medium requires
one additional can called vapour fan for each mill.
If air is used for drying, one fan called mill fan can
be designed to carry out both the functions of
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primary air fan and vapour fan.
 This system favours the following advantages:
a) Mill can be operated always at full load, thus
saving in power, maintenance cost per tonne of
coal for the selected mill. Hence this system is
adopted normally for tube ball mill.
b) Separate spare mill is not necessary for
carrying out the maintenance. Certain
percentage as spare capacity on total basis is
normally enough.
c)
Mills can be operated during off peak hours
only and hence higher power out during the
peak period.
Methods of Fuel Firing
There are many ways of firing the coal in furnace.
They are:
a) Vertical firing
b) Horizontal firing
c) Impact firing
d) Corner or tangential firing
Vertical Firing
 In vertical firing, a number of rectangular fan
shaped nozzles are set across the width of the
furnace in an arc immediately under the boiler
setting.
 The pulverised fuel mixture ignites under the arc
and is directed vertically downwards to the bottom
of the furnace where the gases are made to turn
upwards to pass through the combustion chamber
this gives a long path to the flame and is
particularly suitable for coals of low volatile
content.
Horizontal Firing (Front Firing)
 Horizontal firing with the turbulent type of burner
is set up usually in the front (front wall fired) or
rear walls of the furnace.
 This burner consists of an inner cone for primary
air and fuel which is given a rotary motion as it
passes through the burner. This mixes with a
stream of rotating secondary air before burning.
Impact Firing
This is the arrangement with the type of burner used
with slag tap furnaces where the ash is kept in a
molten state on the furnace floor and tapped off as and
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when necessary.
Corner or Tangential Firing
 Tangential firing is a method of firing a fuel to heat
air, which is the most common one in thermal
power
 Stations.The flame envelope rotates ensuring
thorough mixing within the furnace, providing
complete
combustion
and
uniform
heat
distribution.
 The most effective method for producing intense
turbulence is by the impingement of one flame on
another. This action is secured through the use of
burners located in each of the four corners of the
furnace, close to the floor or the water-screen. The
burner nozzles are so directed that the streams of
coal and air are projected along a line tangent to a
small circle, lying in a horizontal plane, at the
centre of the furnace. Intensive mixing occurs
where these streams meet. A scrubbing action is
present which assures contact between the
combustible and oxygen, thus promoting rapid
combustion and reducing carbon loss. A relative
motion, similar to that of a cyclone, is imparted to
the flame body, which spreads out and fills the
furnace area. The ignition at each burner is aided
by the flame from the preceding one.
 With tangential firing the furnace is essentially the
burner, consequently air and coal quantities need
not be accurately proportional to the individual
fuel nozzle assemblies. Turbulence produced in the
furnace cavity is sufficient to combine all the fuel
and air. This continuously insures uniform and
complete combustion so that test performance can
be maintained throughout daily operation. With
other types of firing the fuel and air must be
accurately proportioned to individual burners
making it difficult to always equal test results.
 With this type of firing, combustion is extremely
rapid and short flame length results. The mixing is
so intense that combustion rates exceeding 35,000
Btu/ (ft3·h) or 360 kW/m3 are practical under certain
conditions. However, since there is considerable
impingement of flame over the furnace walls it is
absolutely necessary that they be fully watercooled. This sweeping of the water-cooled surfaces,
in the furnace, by the gas increases the evaporation
rate. Thus, in addition to absorption by radiation
from the flame envelope, there is transfer by
convection, and the resulting furnace temperatures
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are lower than with other types of burners, even
though the heat liberation rates may be somewhat
higher. Tangentially-fired furnaces are usually
clean in the upper zone and, as a result, both the
furnace and the boiler are comparatively free from
objectionable slag deposits.
Brief Explanation of Tangential Fuel Firing
System
 In this system, burners are set at each corner of the
furnace and are directed to strike the outside of an
imaginary circle in the centre of the furnace.
Because the streams of fuel so strike each other,
extremely good mixing is obtained.
 Since the body of the flame produced is given a
rotary motion it leads to a longer flame travel and
the gases spread out-and flows through
combustion chamber.
Burners and Burner Arrangement
Coal burners mainly comprise of coal nozzle, steel tip,
seal plate and tilting link mechanism. These are
housed in coal compartment in all four corners of the
furnace and connected with coal pipes. Coal nozzle's
one end (outlet) is rectangular and another end is
cylindrical. The rectangular end which forms the
nozzle is connected with nozzle tip by pivot pin. The
tip can be tilted on this pivot. The nozzle tip is divided
into several sectors to form separate coal and air
International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
passages. Again coal and air passages are divided into
several parts for uniform distribution of flow. To seal
the air and coal passage a seal plate is provided.
Oil Burner Design Considerations
The essential requirements for an oil burner design are:
a) It must completely atomise the oil without -drooling,
fouling or clogging.
b) The jet must be so shaped that it will completely
mix with the air necessary for combustion.
c) Maintenance of atomisation over a comparatively
wide capacity range.
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c) Mechanically atomised burners
Air Atomising System
The air atomising system uses compressed air at 7 kg/
sq.cm. The quantity of air required depends on design
of burner, degree of atomisation required, grade of oil,
its pressure and temperature. The air used in the
system should be free of condensate. Air atomising
systems are not recommended for heavy oil system as
they tend to chill the oil and decrease atomisation
quality. The guns used in this system have two main
components for atomisation.
They are:
d) Combustion must be complete and excess air at a
minimum over the entire operating range.
a) Mixing plate
b) Spray Plate.
e) A ready accessibility for effecting repairs, thereby
minimising burner outage as well as maintenance
costs.
The role of mixing plate is to mix the air and oil
properly and the role of spray plate is to inject this
mixture uniformly into the furnace.
Mechanical Atomisation
Oil under pressure is supply to the burner gun and
enters the atomiser tip through slots cut tangentially to
the periphery of the Whirling. The drop pressure is
converted into velocity causing the oil to enter the
whirling chamber at a very high speed, thus
establishing a rapid rotation of the oil in the whirling
chamber.
Atomisation
Atomisation breaks the fuel into fine particles that
readily mixes with the air for combustion. Oil should
be divided up into small particles for effective
atomisation. The advantages of atomisation are:
a) Atomising burners can be used with heavier grades
of oil.
b) Can be adopted to large applications because of
large capacity range.
Since the mechanical atomisation oil guns are limited
in range they are generally selected for boiler
operating at fixed loads.
Steam Atomisation
This system uses auxiliary steam to assist in the
atomisation of the oil. The steam used in this method
should be slightly superheated and free of moisture.
As in the air atomising system, the steam used for
atomising as well as the fuel pass through the tip and
into the furnace. The main advantages of steam
atomising burners over other are:
Classification
a) Simplicity of its design
b) Initial cost of installation is low
c) Low pumping pressure
d) Low preheating temperature.
Oil burners are classified according to the method
used for atomization, as follows:
The only disadvantage is the steam consumption in
burners.
a) Air-atomised burners
b) Steam-atomised burners
Refer the figure below for air / steam atomised oil gun
compartment with wind box assembly.
c) Complete combustion .is assured by the ability of
the small particles to penetrate turbulent combustion.
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
Burner Arrangement
There are twenty four pulverised coal burners
arranged on the corners at a height of 18 to 25 meters
and twelve oil burners provided each in between two
pulverised fuel burners.
The pulverised coal burners are arranged in such a
way that six mills supply the coal to burners at 4
corners, of the furnace, all the nozzle of the burners are
inter linked and can be tilted as a single unit from +30
deg. to -30 degree.
The oil burners are fed with heavy fuel oil till boiler
load reaches to about 25%. There are four wind boxes
fixed at 4 corners of the furnace. There are 13 nozzles
in each wind box 6 for coal and 7 for air.
In tangentially fired boilers, four tall wind boxes are
arranged at each corner of the furnace. The coal
burners are located at different elevations of wind
boxes. The numbers of coal nozzles elevations are
equivalent to the number of coal mills. The same
elevations of coal nozzles at four corners are fed from
a single coal mill.
 The coal nozzle is sandwiched between air nozzles
or compartments. That is, nozzles are arranged
between coal nozzles, one below the bottom coal
nozzle and above the top coal nozzle. If there are
‘n’ numbers of coal nozzles per corner there will be
(n+1) number of air nozzles per corner.
 The coal fuel and combustion air streams from
these nozzles directed tangential to imaginary
circle at the center of the furnace. This creates
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turbulent vortex motion of the fuel, air and the hot
gases which promotes the mixing, ignition energy
availability and thus combustion efficiency.
 All the nozzles of the burners are interlinked and
can be tilted as a single unit from +30º to -30º.
 The air nozzles in between are termed as
“Auxiliary air nozzles”, and the topmost and the
bottommost air nozzles are termed as “End air
nozzles”.
 The coal nozzles elevations are designed as A, B, C,
D, E, F, G, and H from bottom to top, the bottom
end air nozzles as AA, and the top end air nozzles
as HH. The auxiliary air nozzles are designated by
the adjacent coal nozzles as, like AB, BC, CD, DE,
EF, FG, GH and HH from bottom to top.
 The four furnace corners are designated as 1, 2, 3
and 4 in clockwise direction looking from the top,
and counting front water wall left corner as ‘1’, as
shown in the figure below.
 Each pair of coal nozzle elevation is served by one
elevation of oil burners located in between the
auxiliary air nozzles. In this with the eight mills or
eight elevations of coal nozzles, there are 16 oil
guns arranged in four elevations at auxiliary air
nozzles at AB, CD, EF and GH.
 Heavy fuel oil can be fired at the oil gun elevations
and L.D.O can be fired only in AB elevation. Each
oil gun is associated with an igniter arranged at the
side.
International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
Typical Corner Arrangement for a
Tangentially Fired System
S.NO
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
CORNER -1, 2, 3, 4
H H
AIR
H
COAL
G H
OIL
G
COAL
F G
AIR
F
COAL
E F
OIL
E
COAL
D E
AIR
D
COAL
C D
OIL
C
COAL
B C
AIR
B
COAL
A B
OIL
A
COAL
A A
AIR
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Coal Nozzel
MILLS
Nozzle are the place from where primary air and coal
sent to Boiler.
G H
In a power Station there are two type of coal nozzle
used.
E F
C
D
A B
1) Impellor: - Impellor type nozzle is used in first
stage unit.
•
•
•
•
•
•
It is based on Italian design.
Oil gun is used in impellor type nozzle
In impellor the upper side is diamond shaped.
The length of impellor is 1900 mm.
7018 no electrode rod is used for welding in
impellor type nozzle.
For patching 6013 no electrode rod is used.
2) Tangential: - Tangential coal nozzle is used in 4th,
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International Journal of Automation and Control Engineering (IJACE) Volume 3 Issue 3, August 2014
5th, 6th and 7th unit.It is used in corner firing.
Details of Nozzle
Weight:
Cost of one nozzle = 350000 Rs
Total no of nozzle used in one boiler = 32
Hence, total cost = 32x350000
= 11200000 Rs
The weight of nozzle is 991kg.
The cost for repairing one nozzle is approximately
10000
Length:
Cost of repairing one nozzle = 10000 Rs
Tip to nozzle is 2400mm.
Total no of nozzle = 32
Tip:
Hence, total repairing cost = 320000 Rs
Tip of nozzle is 800mm square
As for new nozzle 11200000 Rs is required and its life
is 2 years. But for repairing it costs 320000 Rs.
Nozzle Outer Diameter:
The outer diameter of nozzle is 640mm.
1
2
3
4
5
IGNITER GUNS
4 X 8 = 32
OIL GUNS
4 X 4 = 16
COAL BURNERS 4 X 8 = 32
SCANNERS IR (COAL) 4 X 4 = 16
SCANNERS UV (OIL)
4 X 4 = 16
Filler
Cobal Arc is used as filler.
•
•
•
•
For metallic filler 7018 no electrode rod is used.
For joining divider 604 no electrode rod is used.
For welding stainless steel 308 and309 no electrode
rod is used.
For making diamond shape 604 no electrode rod is
used for preventing from erosion.
Hence saving = 11200000-320000
= 10880000 Rs.
Conclusion
A thorough examination and keen study on the
various fuel igniters, burners and the fuel firing
systems have been observed in UNIT 4 & 5 of stage II
in RSTPS. In addition, we have also observed the
various flow processes taking place in the boiler and
its auxiliaries.
REFERENCES
www.ntpc.co.in
www.google.co.in
www.bhel.co.in
Cost of Tangential Coal Nozzle
Wikipedia
• The cost of one tangential coal nozzle is 350000 Rs
Few other sources available online
Total number of nozzle used in one boiler is 32.
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