boiler burner

7/23/2019 Boiler Burner

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Consists of settling

tanks two fuel oil units

comprising suction filter,pressure pump with

attached air vessel,

discharge filter and

heater.Each fuel oil unit

is capable of supplyingfuel for generating the

steam required for all

purposes at sea. The

second unit is

maintained as a

standby.

Boiler fuel oil system

The hot fuel is delivered to the boiler fronts through a pressure line which is

fitted with a circulating valve and return line to the suction side of the fuel

units.An emergency pump from Diesel il connection and an electric heater

are also fitted for lighting up when no steam is available.



The heat producing constituents of the fuel are hydrogen, carbon and

sulphur.

The calorific value of the combustion processes measured in mega joules for each Kg of fuel burnt

Carbon to carbon dioxide - 34

ydrogen to !ater - "#$.% & assuming the !ater vapor is not allo!ed to

condense' (ulphur to sulphur dioxide - ).3

The main cause of heat loss !ith the process is that ta*en a!ay by

nitrogen. Therefore, to achieve maximum efficiency the excess air should

be *ept to a minimum. o!ever there is a limit to the reduction in the

excess air in that the combustion process must be fully completed !ithin

the furnace and !ithin a finite time.

The main type of combustion process is called the suspended flame.

The flame front remains in the same position relative to the burner and

+uarl. The fuel particles pass through the flame completeing theircombustion process and exiting at the same rate as the fuel entering.

Combustion of fuel



!The oil is heated in steam or electric heaters, this reduces the

viscocity for better pumping,filtering and atomiation. il not to be

over heated to prevent crac*ing !hich eads to carbon deposits, andthe formation of gas in the fuel oil reduces the mass of oil passing thro

the burners, !hich in turn reduces the steam rate in the boiler.

!The gasification also causes instability in the combustion resulting

fluctuating flame formation. The heated oil is atomied in the furnace

by the burners !hich brea*s oil into fine particles !hich forms a fine

mist and slightly larger droplets formed by the heavier fractions of the

residual fuel

!The burner also imparts rotational energy to the fuel so that it leaves

the burner of fine droplets of oil.!The combustion one itself can be divided into t!o main stages

namely /rimary and secondary flame.

Combustion of fuel



Cumbustion1



cumbustion2

cumbustion2



Primary Flame-To burn oil the temperature must be raised tovaporisation temperature, this can not be done in heaters due togassing but is done by radiant heat in the flame. The lighter hydrocarbons in the atomised spray are rapidly heatedand burnt in the primary flame. The heavier fractions pass through this achieving their vaporisationtemperature.

The primary flame is essential to good combustion. By design theprimary flame exists where it receives maximum reflected heat fromthe shape of the quarl.The size of the primary flame ( shown smaller than actual indrawing !ust fills the quarl space.

Too large and impingement leads to carbon deposits building up.Too small unheated secondary air reduces combustion efficiency. The tip plate creates vortices reducing the mixing time for theair"fuel and reduces the forward speed of the flameSecondary Flame-#ere the heavier fractions are burnt. The

velocity of the air and fuel must be matched to the required flamepropogation rate.

Peimary and secondary ame.



Burner to present the fuel in suitable condition forproper combustion.

Burner atomises the fuel and giving it some axial(for penetration and angular (for mixing velocity.

$or effective atomisation the viscosity of the fuel is

critical, for fuels heavier than gas or diesel oils somedegree of heating is required. %t should be noted thatthe temperature of the fuel should not be allowed toraise too high as this can not only cause problem with

fuel booster pumps but also can cause flame instabilitydue to premature excessive gassification.

The smaller the droplet size the greater the surfaceareas"volume ratio is, this increases evaporation,

heating and combustion rate

Fuel



"lame burning off the tip may occur after initial ignition or

after a period of high excess air.

The effect of this is to move the primary flame awayfrom the quarl thereby effecting the combustion process

leading to blac& smo&e and flame instability.

Two methods of bringing the flame bac& are

'.To reduce excess air and introduce a hand ignitor to

ignite the fuel correctly.

. To rapidly close then open the register damper

Flame burning of the tip



There are six main types of burner in common use

/ressure jet

(pill type pressure jet

0ariable orifice pressure jet

(pinning cup

(team assisted

1ltrasonic

Turndo!n ratio ratio of minimum to ma#imum flow roughly th

square root of the ratio of ma#imum to minimum pressure

Boiler burner



This is the simplest and oldest design of burner.

Atomisation of the fuel is achieved by forcing the fuelunder pressure through an orifice at the end of the burner.

The pressure energy in the fuel is converted to velocity.

$pin is given to the fuel prior to the orifice impartingcentrigual force on the spray of fuel causing it to atomise.

Pressure jet



The advantage is that it does not require anyassistance other than supplying the fuel at the correctpressure.

)ue to this it is still seen even on larger plant wereit is used as a first start or emergency burner.

The disadvantage of this burner is its low *Turn-)own* ratio (in the region of +..

nother disadvantage over assisted atomisationburners is the lac& of cooling from steam or air meansthe burner must be removed when not in use from litboilers to prevent carbonising in the tube

Pressure jet



The method of atomisation is the same as for simplepressure %et type. The burner differs in that a proportion

of the supplied fuel may be spilled off. This allows for

increased turn down ratio

Spill type



$uel ressure entering the burner acts against aspring loaded piston arrangement.

%ncreasing pressure causes the piston to pull a

spindle away from the tip, this has the effect ofenlarging a closed swirl chamber and uncoveringports.

tomisation efficiency is maintained over a greater

fuel supply pressure range

&ariable orifice pressure %et



$uel is suplied to a standard pressure tip atomiser. /team passesaround the fuel passage and exists through an open annulus havingbeing given an angle of swirl to match the fuel spray.

t low fuel pressure the steam, supplied at constant pressurethroughout turndown, provides for good atomisation.

t higher fure pressure the pressure tip provides for theatomisation.

$or first start arrangements compressed air may be used

Steam assisted burners



#ere the steam and fuel are mixed into an emulsionand expanded in the holes before emission creatinggood atomisation.

This design is tolerant of viscosity changes and isfrugal on steam consumption and require reduced fuelpump pressures

Y jet burner



The main advantage of this design over the *0* !et is thereduced *bluff* zone due the reduced pitch diameter of theexit holes.1atched to a venturi register, a very stable efficientflame is formed. The $uel"/team mix exits the nozzle in a series of conic

tangents, fuel reversals inside the fuel cone allow efficientmixing with air over a wide *Turn-)own ratio (23'. %n addition this type of nozzle is associated withreduced atomising steam consumption (2.24g per 4g

fuel burnt 0enturi and conventional register throat design

Se! jet burner



'anufactured by (awasaki )ider turn down ratio with lower

e#cess air *+ -+

/ow 0 levels , $implified operation 1educed acid corrosion

problems

Atomisation is achieved primarily by the energy of ultrasonic

waves imparted onto the fuel by the resonator tip which vibrates ata frequency of '23 to 04 '23 under the influence of high speedsteam or air impinging on it.

E#tremely small droplet si3es result which allow for a very stable

flame

"ltrasonic burner

$ l i i t d d t th



Spinning cupburner

$uel is introduced onto the

inner running surface of a highly

polished fast spinning cup (+ to

5222 rpm.

6nder centrifugal force this

fuel forms a thin film.

)ue to the conical shape of the

cup the fuel flows to the outer

edge spilling into the primaryatomising air stream.

The fuel is bro&en into small

droplets and mixed with the

primary air supplied by the shaftmounted fan.

/econdary air is supplied by an external fan for larger units.

ac&aged units of this design have the air flow valve controlled by

the fuel supply pressure to the distribution manifold.



The spinning cup offers the following advantages5)ider turn down ratio with lower e#cess air

/ow 0 levels

6o requirement for atomising air or steam

/ow fuel pressure requirements to an e#tent that gravity flow

is sufficient

stable flames achievable with very low fuel flows although

ma#imum flow limited by si3e of cup. This, allied to being

limited to side firing making the design more suitable for

smaller installations.

$pinning cup burner



7lue flame burner

This highly efficient and clean burning method.

6nder normal conditions a portion of the hot gassesfrom the combustion process is recirculated.

$uel is introduced into the gas were it is vaporised.

The resultant flame is blue with little or no smo&e



(2/ /5((15 6T

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The pressure head of the fuel is

converted into velocity head as itpasses through small tangential in the

atomi3er tip. 8n addition the holes

imparts a swirling motion to the oil, the

discharge from the no33le being

broken up in to fine mist by centrifugal

force

7urner similar to pressure atomiser

in addition a leak off is provided

from the swirl chamber.The oil

enters centrally and spill oil leaves

through annular passage in theburner body.7y increasing the

amount of leak off the amount of oil

that is delivered to the furnace is

reduced with out seriously imparing

the atomisation.

7oiler burner+

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&A18A7/E 18"8CE 7916E1$

The variable orifice burner utilises

variations in fuel pressure to increase or

decrease its output. An increase in oil

pressure forces the spindle to the rightagainst the action of the coil spring

uncovering an increased number of

tangential holes in the spray plate.

$:86686; C9: 7916E1

The assembly consists of a tappered cupfitted on to the end of a central rotating

spindle mounted on ball or roller bearings

the fuel oil is supplied to the inner surface

of the cup through the hollow end of the

spindle .The centrifugal force causes it to

spread out evenly into a thin film ,whichthen moves out along the taper until it

reaches the lip of the the cup,where the

velocity causes to break up into fine

particles.the final result is a hollow rotating

cone of oil droplets leaving the burner.

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The steam flows along the central passage and is then e#panded through

convergent divergent no33le )here its pressure energy is converted to kinetic

energy resulting in a high velocity %et of steam. il sprayed in to this %et is beingtorn to shreds and atomised in the process The e#it ports are arranged

tangentially thus giving the necessary swirl to the oil droplets in order to form the

hollow rotating cone of fin particles of oil needed for the efficient combustion.The

through put of oil is controlled by varying the oil supply pressure. Care must be

taken to use only dry steam, any water present will cause flame instability.$afety

shut of valves are fitted in the burner carrier so that oil and steam areautomatically shut off when the burner is removed.

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# i t



1egister supplies the correct quantity of e#cess air.

Too little allows incomplete combustion, smoking, sootdeposits and flame instability.

Too much e#cess air,

+. 1educes combustion efficiency by removing heat from thefurnace space, may cause @white@ smoking and promote

sulphurous deposits.

0. 8ncreases the proportion of sulphur trio#ide to dio#ide

promoting increase acid corrosion attack in the upper regions.

The register and to some e#tent the quarl determine the shape

of the flame, short and fat for side fired boilers, long and thin

for roof fired.

#egister

$i h t



$ir heaters

These are fitted for three main reasonsTo increase efficiency by recovery of heat from flue gases

Accelerate rate of combustion Avoid effect of cold air impinging on boiler surface As a by product air heaters also form a convenient way to warm

up a standby boiler before initial firing.

The effects of dew point corrosion and fouling in smoke tube airheaters should be taken into account when designing the heat

absorption limit.*the amount of heat to be removed from the flue

gas should have a limit."or water tube boilers gas air heaters are only considered where

the temperature at inlet to economiser is greater than 044oC. Due

to greater heat transfer efficiency between gas water,

economisers are preferred to gasair e#changers.t low loads all gas"air heaters should be bypassed to

&eep upta&e temperatures as high as possible.



The drum contained within the cylindrical casing isformed into segments into which are placed removable

( for cleaning bas&ets, consisting of vertical plates (togive minimum resistance to flow The drum slowlyrotates, about 7rev"min, driven via a flexiblecoupling,gear train, clutch and thrust bearing by one of

two electric motors8 one mounted on top the other

$ir heaters1

i h 2



s the drum rotates a segment will enter the gas side, here itremoves heat from the gas, it continues to rotate until entering theair side where it will give up its heat to the air. The heat transfer is

very efficient, however, soot and corrosive deposits quic&ly build upin the mesh and hence an effective soot blowing method is essential.This normally ta&es the form of an arm , pivoted at the circumferenceof the drum with a single nozzle at the other end. This sweeps acrosthe drum rather li&e a record arm. 9ne of these arms are fitted top

and bottom.

$ir heaters 2

$ir heaters %



:as lea&age to the air side is prevented by the air being at a higherpressure and by fine radial clearance vanes fitted in the drumsegments.

By passes for both air and gas sides are fitted to prevent fouling withthe reduced gas flow and temperature, also during manoeuvringwhen the possibility of different gas"air flow rates occurring leadingto high metal temperatures and possible fires.

$ailure by upta&e fires is not uncommon with this as in most gas"airheater designs.

$ir heaters %

& b i h t



The horizontal tube type air heater which was lesssusceptible to cho&ing with soot than the vertical typessometimes found with older scotch boilers.

;ater washing was sometimes carried out to aid the

soot blowers

&ube air heater

" tube air heaters



The use of individual ban&s and *6* tubes allow for easeof isolation when these become perforated without largeloss of heating surface. The tubes were expanded intothe headers and made of cupronic&el with copper fins.

" tube air heaters

boiler burner

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