Fuel System
13 April 2015
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Presentation Plan
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Fuel oil System
Oil burners
Coal mills and feeder
Types of feeders
Classification of Mills
Features of different Mills
Burner arrangement
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Fuel oil System
• Purpose: (a) to establish initial boiler light up. (b) to
support the furnace flame during low load
operation.
• Fuel oil system Consists of
• Fuel oil Pumps
• Oil heaters
• Filters
• Steam tracing lines
Objective is to get filtered oil at correct pressure and
temperature
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Atomization
• Atomization breaks the fuel into fine particles that
readily mixes with the air for combustion. Oil should be
divided up into small particles for effective atomization.
The advantages of atomization are:
a) Atomizing burners can be used with heavier grades of
oil.
b) Can be adopted to large applications because of large
capacity range.
c) Complete combustion is assured by the ability of the
small particles to penetrate turbulent combustion.
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Classification: Oil burners
Oil burners are classified according to the method
used for atomization, as follows:
a) Air-atomized burners
b) Steam-atomized burners
c) Mechanically atomized burners
Air atomizing system are not recommended for heavy
oil system as they tend to chill the oil and decrease
atomization quality
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Steam Atomization
This System uses auxiliary steam to assist in the atomization
of the oil. The steam used in this method should be slightly
superheated and free cf moisture. As in the air atomizing
system, the steam used for atomizing as well as heating the
fuel as it pass through the tip and into the furnace. The main
advantages of steam atomizing burners over other are:
a) Simplicity of its design
b) Initial cost of installation is low
c) low pumping pressure
d) low preheating temperature.
Disadvantage is steam used in atomizing process
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Oil Burners
The types of oil used in the oil burners are:
a) Light Diesel Oil
b) Heavyfuel oil
c) Low sulpher heavy stock (LSHS).
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 ignitor are
used for start up and oil flame stabilizing.
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Oil Guns
The guns used in this
system have two main
components for
atomization. They are:
a) Mixing plate
b) Spray Plate.
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Oil Gun Compartment
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Coal Mill & Feeder
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Components
The Major components are :
• Coal Preparation Equipments
• Feeders
• Mills
• Coal Firing Equipments
• Burners
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Feeders
• Volumetric Type feeder
• Chain Feeder
• Belt Feeder
• Table type belt Feeder
• Gravimetric Feeder
Chain
Feeder
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Gravimetric Feeder
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CLASSIFICATION OF MILLS
XRP
(BHEL)
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VERTICAL SPINDLE
TUBE
BOWL/
BALL & RACE
PRESSURIZED
E MILLS
(BABCOCK)
MPS
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Classification-As per Speed
Types of Mills
Low Speed
Medium Speed
High Speed
17 to 20 Rev/min
30 to 100 Rev/min
500 to 1000 Rev/min
Tube and ball mill
Bowl Mill, Ball and
Race mill
Beater Mill, Impact
Mill
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BOWL MILL
Model no.
623XRP
703XRP
763XRP
803XRP
883XRP
903XRP
1003XRP
1043XRP
Base
capacity(T/Hr)
18.4
26.4
33.8
36.5
51.1
54.1
68.1
72.0
BASE CAPACITY(T/HR)
AT
HGI -55
Total Moisture-10%
Fineness-70% THRU 200
MESH
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Features of Bowl Mills
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Grinding chamber
Classifier mounted above it
Pulverization takes place in rotating bowl
Rolls rotating free on journal do the crushing
Heavy springs provide the pressure between the coal and
the rolls
• Rolls do not touch the grinding rings
• Tramp iron and foreign material discharged.
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Pictures of Bowl Mill
Coal Entry
Hot Air
Flow from
PA Fan
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Classifiers
To burners
Rollers
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Typical Mill (Pulveriser)
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Internal
Details of a
Mill
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BALL& RACE MILL(E MILL)
Model no.
7E9
8.5E10
8.5E9
10E10
10.9E11
10.9E10
10.9E8
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Base
capacity(T/Hr)
25
35
40
55
61
70
80
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TUBE MILL
Model no.
BBD4760
BBD4772
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Base
capacity(T/Hr)
83
90
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Tube Mill Internals
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Feature of Tube Mill
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Operate at 17 to 20 Rpm
Coal Feed from both end of the Tube
Small Ball of 30,40, 50 mm Sizes are used
Hot air blown to move coal to classifiers at two elevations
in boiler furnace
No Maintenance for long periods
Better availability so no spare mill required
Always a reserve of coal so there is no spark produced
between Steel balls
Consumption of power is more
High Foundation and Initial cost of Equipment
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RC Feeder
Classifiers 4 No.
Drum Feeder
Classifiers Distributors
2 No.
Hot Air
Entry
Ball and Tube Mill
Coal entry to Drum
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Pictures of Tube Mill
Steel Balls
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Role of Mills
• Produces Pulverized coal 80% of which passes through
200 mesh
• Air mixed with Pulverized coal (PF) is carried to the coal
nozzle in the wind box assembly.
• PF from coal nozzle is directed towards the centre of
boiler burning zone
• Pre-heated secondary air enters boiler and surrounds the
PF and help in combustion
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Why Pulverized Fuel?
The economic motives for the introduction and
development of pulverized fuel firing are:
i) Efficient utilization of cheaper low grade coals.
ii) Flexibility in firing with ability to meet fluctuating loads.
iii) Elimination of breaking losses.
iv) Better response to automatic control.
v) Ability to use high combustion air temperature;
increasing the overall efficiency of boiler.
vi) High availability.
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Mill Dampers and
air system
• PF temperature to be maintained
900C
•All Shut off valves are required to be
kept wide open during operation
•Mill bearing is to be kept clean and
no dust should enter
•Low Primary air flow will cause
unstable flame and high flow result in
high mill reject
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Burner
Arrangement
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Firing System
• Direct Firing System: Coal is fed to the mill at
controlled quantity. Hot air (temperature controlled) is
permitted to flow through the mill. The air dries the coal and
picks up the milled product and flows through the classifier
rejecting higher size particle. The fine coal is carried
through the coal burner to the combustion chamber.
• Indirect Firing 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.
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Direct Firing
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Indirect Firing
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Coal Burners
• Coal burners comprise of coal nozzle, steel tip, seal
plate and tilting link mechanism.
• Housed in coal compartment in all four corners of the
furnace and connected with coal pipes.
•One end (outlet) is rectangular and another end is
cylindrical.
•The burner can be tilted on a pivot pin
•. The nozzle tip has separate coal and air passages.
• Coal and air passages is divided into sevaral parts
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Methods of Fuel Firing
Vertical Firing : A number of rectangular fan shaped nozzles are set
across the width of the furnace in an arch. Pulverised fuel mixture ignites
under the arch 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: Horizontal firing with the turbulent type of burner are
set up usually in the front (front wall fired) or rear walls of the furnace.
Burner consists of an inner cone for primary air and fuel which is given a
rotary motion as it passes through the burner.
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 when necessary.
Corner or tangential Firing: 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.
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Tangential Firing System
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Arrangement
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Typical Flame
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Various Losses in A Boiler
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Heat loss from furnace surface.
Unburned carbon losses.
Incomplete combustion losses.
Loss due to hot ash.
Loss due to moisture in air.
Loss due to moisture in fuel.
Loss due to combustion generated moisture.
Dry Exhaust Gas Losses.
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THANK YOU
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