April 18, 2023 1

Fuel System

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April 18, 2023 2

Presentation Plan• 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 designb) Initial cost of installation is lowc) low pumping pressured) 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 Oilb) Heavyfuel oilc) 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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ComponentsThe 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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XR P(B H EL)

E M ILLS(B AB C O C K )

M PS

B O W L/B ALL & R ACE

VER TIC AL SPIN D LE

PR ESSU R IZED

TU B E

C LASSIFIC ATIO N O F M ILLS

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Classification-As per Speed

Types of Mills

Medium Speed High SpeedLow Speed

17 to 20 Rev/min 30 to 100 Rev/min 500 to 1000 Rev/min

Tube and ball mill Bowl Mill, Ball andRace mill

Beater Mill, Impact Mill

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BOWL MILL

Model no. Base capacity(T/Hr)

623XRP 18.4703XRP 26.4763XRP 33.8803XRP 36.5883XRP 51.1903XRP 54.11003XRP 68.11043XRP 72.0

BASE CAPACITY(T/HR)AT HGI -55Total Moisture-10%Fineness-70% THRU 200 MESH

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Features of Bowl Mills• 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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Rollers

Coal Entry

Hot AirFlow from PA Fan

ClassifiersTo burners

Pictures of Bowl Mill

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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. Base capacity(T/Hr)

7E9 258.5E10 358.5E9 4010E10 5510.9E11 6110.9E10 7010.9E8 80

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TUBE MILL

Model no. Base capacity(T/Hr)

BBD4760 83BBD4772 90

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Tube Mill Internals

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Feature of Tube Mill• 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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Ball and Tube Mill

RC Feeder

Drum Feeder

Coal entry to Drum

Classifiers Distributors 2 No.

Classifiers 4 No.

Hot AirEntry

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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

• 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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