firing system4

8/12/2019 Firing System4

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SEMINAR REPORT

ON

210 MW LMW

WIND-BOX

DESIGN

&

OPERATION

(For Induction Level Training Course for Engineers)

2008

SUBMITTE B!

ASHOK D. WALKOLI

Junior Engr. (Gen)

K-45 Batch

COURSE DIRECTOR COURSE CO-ORDINATOR

Mr. P.D. Deshmukh (E.E.) Mr. M.H. Deshpande (Dy.

E.E.)

KORADI TRAINING CENTER


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MSPGCL, KORADI, NAGPUR.

"C#$%&LE'ME$T

I am very glad to express my deep sense of gratitude and whole

hearted thanks to Mr C S&"M! (C'M)and Mr BU &"'M"*E

(SE) for giving me encouragement and necessary facilities for carrying out

this seminar.

I am also thankful to Mr + ESMU# (EE)Course Director

& Mr. M ES+"$E (, EE) Course Co-ordinator who has

provided me this opportunity to do the same. Last ut not the least! I would

like to thank all the related people who helped me in the duration of my

seminar.

"S%# &"L#%LI

-rEngr ('en)

#./ Batc1

KORADI TRAINING CENTER


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MSPGCL, KORADI, NAGPUR.

I$E

34 C%MBUSTI%$ "$ &I$.B% "I*

24 C%MBUSTI%$ "I* S!STEM

54 FUEL BU*$I$' S!STEM 6 SUBS!STEMS

/4 SEC%$"*! "I* S!STEM 6 IST*IBUTI%$

4 %+E*"TI%$ %F &I$.B%

74 +*%UCTS %F C%MBUSTI%$ S!STEM

4 I$ST*UME$T"TI%$ L%'ICS

84 +*%BLEMS &IT &I$.B%

94 C%$CLUSI%$


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34 C%$T*%L %F &I$B% "I* T% B%ILE* 6 C%MBUSTI%$ TE%*!

Coal is fired in to the furnace where comustile matter in the coal reacts with

"xygen from the comustion air. Chemical reaction causes release of heat energy. #s a

result of comustion$ %lue gases and ash is also generated$ which are removed from the

furnace y I.D. %ans. #sh is separated from flue gases in lectrostatic 'recipitator and

flue gases are released in to atmosphere. %ly ash is evacuated from (' )oppers and

disposed off to ash und. (ulphur present in the coal reacts with "xygen producing ("*

and ("+ gases$ which mix with moisture$ forming (ulphuric acid$ which has a due point

of ,* C. If flue gas temperature drops elow due point temperature$ condensation of

(ulphuric acid take place causing corrosion of the steel work. )ence flue gas temperature

is maintained around ,+/ C to ,0 C at #ir 'reheater outlet. %lue gases at the

temperature of ,+/C to ,0C are then released to atmosphere. 1his causes loss of heat

energy$ and the loss is called 2Dry %lue 3as Loss4. 1his loss is minimum if 5uantity of

flue gas released is minimum. 6uantity of flue gas produced is proportional to 5uantity of

comustion air supplied. %or complete comustion of fuel$ certain minimum air is

re5uired and there are thus limitations in reducing the air 5uantity. Comustion system of

7oiler is designed to achieve complete comustion of all the fuel with 2optimum4 air

supply. Comustion system design also takes care that flue gas temperature shall remain

within ,+/ C to ,0 C at #ir 'reheater outlet. 1o develop a understanding of the

comustion process is the o8ective of this write up. (ome of the terms commonly used in

comustion theory are defined as follows.

Initiation of Co:;ustion in ;oiler9

%or comustion to take place there are three essential re5uirements %uel$ #ir and

Ignition. Ignition energy re5uirements for coal are high and can not e met y low energy

devices such as electrical spark plugs etc. )ence coal is never fired at start up of the

oilers. "n the other hand$ LD" :Light Diesel oil; is used to initiate start up of the 7oiler


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as its ignition energy re5uirements can e fulfilled with the help of lectrical spark$

otained from spark plugs. ery high rate of fuel admission re5uired for achieving re5uired evaporation rate.

(team flow for *, M< 7oilers is ?@ 1onsA hr and for / M< oiler$ it is ,/*0 tons A

hr. 1he fuel firing rate for these oilers are ,+/ 1A)r and + tons A hr respectively. Coal

particles do not stay in the furnace for more than , or * seconds. )ence$ comustion

system shall e ale to complete comustion of all the fuel within this time. 1he time for

which coal remains in comustion Bone is called esident 1ime.

2)nurnt caron should not exceed ./ = to ,. = of fly ash to achieve high 7oiler

efficiency.

5)>olume of %lue gas generated shall e minimum possile. #s the flue gas is

discharged in to atmosphere at ,+/ C$ small volume of flue gas means small heat losses.

/)#ll these o8ectives shall e achieved keeping the furnace siBe as small as possile for

achieving low capital costs.

)#ll coal particles shall e ale to mix with the "xygen in the comustion air eing

supplied to the furnace.

7)#ir surrounding every coal particle shall contain enough "xygen for its complete

comustion.


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)ow the comustion system achieves these o8ectives can e known y studying

comustion mechanism.

Co:;ustion :ec1anis:4

Co:;ustion of single solid Fuel


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1he process takes place at #tmospheric 'ressure and at very high temperature of ,*

Degrees C or higher and is Diffusion controlled. 1he furnace also contains mixture of

%lue gases$ fly ash and #ir eing supplied.

1he process of comustion progresses in two steps9

,; Delivery of "xygen from the air :which is one of the constituent of mixture of the

gases present in the furnace; to the surface of Coal particles y Diffusion

*; Chemical reaction taking place at the surface.

1he rate of comustion is controlled y the rate of Diffusion of "xygen. %or otaining

very high rate of diffusion of "xygen from air to fuel particles$ it is necessary that fuel

particles must always remain surrounded y air re5uired for complete comustion of the

particles. (ince the furnace contains mixture of air$ coal particles and flue gases$ the

proaility of coal particles remaining in contact with air is very high provided following

re5uirements are fulfilled9

,. (mall siBe of the 'articles9 Coal is pulverised to very fine siBe in coal mills thus

increasing the surface area of per unit mass of coal. #s small particle needs small mass of

air for its complete comustion$ it needs to e surrounded y small siBe of air sphere. In

well-mixed furnace$ it is possile to fulfill this condition. Coal is pulverised to Mean

average 'article siBe of @/ microns. :Corresponding to *-mesh siBe;. @= of coal

particle should pass through *-mesh sieve and retention y /-mesh screen shall not

exceed ,=.

*. Dryness of Coal particles9 'ulverised coal is transported to %urnace through coal pipes

using 'rimary air. Coal is dried in the coal mill with the help of high temperature primary

air. 1he mixture temperature at coal mill outlet is maintained at @/ C$ which prevents

condensation of water vapor in the coalA air stream. >elocity of coal A air mixture in the

pipes is +/ mAsec which avoids separation of particles from stream.

+. >elocity of air A coal mixture in pipes9 1o achieve well-mixed furnace$ e5ual mass of

coal should e fired from all corners. %or making the velocity of airA coal mixture e5ual

in all pipes$ orifices are provided on the pipes.


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Coal contains >olatile matter that mainly comprises of gases such as Methane$ )ydrogen

Fitrogen$ "xygen and moisture. olatile Matter

comes out from the particle and starts urning. "xygen in the 'rimary air gets consumed

in the comustionof volatile matter. (ince volatile matter is gaseous in nature$ it mixes

easily with the air and hence its comustion is very rapid. 1he solid particles$ which are

now devoid of >olatile Matter$ are known as soot particle. Comustion air re5uirement

for soot particles is fulfilled y secondary air. (econdary air fans are used for this$

discharge of which is connected to #ir preheaters$ where air temperature is increased to

+*/ C.

1his air then flows to


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Dampers #$ 7$ C$ D$ % and %9 1hese are also called %uel air dampers. 1he opening of

these dampers is modulated as per mill loading. 1hese dampers supply the secondary air

for comustion of coal and hence open only for those coal elevations$ which are in

service.

Dampers #7$ CD and %9 %or the oil elevations in service$ these dampers modulate as

per the oil pressure. %or the elevation where oil guns in not in service$ these dampers

modulate to maintain %urnace-


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1urulence9 1urulence in the furnace results in well-mixed furnace where the gas

mixture is homogeneous. 1angential corners firing result in highly turulent furnace.

>ortex formed in the furnace due to corner firing causes particles to travel in a helical

path$ thus increasing the resident time.

Firing s,ste:

1he firing system adopted for koradi unit is of direct firing tangential system with

the fuel air mixture from the fuel preparation plant directly carried to the

respective urners without having any intermediate storage ins.

1he tangential tilting urners are located at the four corners with six fuel

elevation$ corresponding to the six owl mills.

In this tangential firing system furnace itself acts as a urner ensuring good

turulence and complete comustion inside the furnace at a fairly low flame

temperature level. 1his also results in minimum emission of Fitrogen "xide

orF"*.

1he urners are e5uipped with tilting mechanism to enale the tilting of the

urner y a range of G+ in order to achieve a finer control in reheat system

temperature at part load conditions. 1he urner windox selected for H"#DI

unit is designed to fire a wide range of Indian coals. Depending on the type ofcoals to e fired the numer of mills and therey the numer of fuel elevation in

operation will vary from 0 to? at MC load condition.

It may e noted that there are two elevation of oil guns sandwiched with coal

compartment for the purpose of start up and warm up re5uirement. 1he capacity

of each oil gun is */= of MC. )owever when oth elevations are in operation$


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the maximum load per elevation is to e maintained at ,*./=. 1he oil heating and

pumping units are siBed for a total */= MC capacity.

1he windox is provided with 0 numers of ignitors and + numer of flame

scanners per corner of location as indicated in the sketch attached. 1hese scanners

and ignitors are linked with the furnace safeguard system :%(((; installed in this

unit to ensure safer comustion.

24 C%MBUSTI%$ "I* S!STEM

1he unit uses two forced draft :%D; fans$ two primary air :'#; fans$ and two

induced draft :ID; fans. 1he %D fans force comustion air through the air heater

then into the windox and steam generator for comustion. 1he %D fans are axial

flow fans that are driven y single-speed electric motors. 1he '# fans force

comustion air through the air heater then through the pulveriBers$ where the

pulveriBed coal is removed efore delivery to the urners. 1he '# fans are

centrifugal fans driven y single-speed electric motors.


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1he steam generator operates at essentially atmospheric pressures. 1he ID fans

develop the pressure differential necessary to remove the comustion gas from the

steam generator. 1he fans propel the flue gas through the air heater$ particulate

removal system$ flue gas desulfuriBation system and up the stack. 1he ID fans are

axial flow fans driven y single-speed electric motors.

54 FUEL BU*$I$' S!STEM "$ SUBS!STEM

1he primary function of fuel urning system in the process of steam generation is

to provide controlled$ efficient conversion of the chemical energy of the fuel in to

heat energy which is then transferred to the heat asoring surface. (atisfactory

oiler operation re5uires energy and se5uence so that the furnace never can

contain an explosive mixture$ flow and processing of fuel$ air ignition energy and

the products of comustion

"I* 6 FLUE '"S S!STEM

Si:


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Su; s,ste:s

1he fuel urning system should function so that the fuel and air input is ignited

continuously and immediately upon its entry into furnace.

1he total fuel urning system re5uires to do this consist of su systems for

#ir handling

fuel handling

ignition

comustion product removal

main urners and oiler furnace

"ir 1andling 1his su system should e capale of supplying properly air to the main urners

on a continuous and uninterrupted asis. It should e capale of providing the

re5uired air fuel ratio over the entire range of the urning.

1he total air re5uired for comustion is divided into primary air and secondary

air. 1he primary air is that portion of the total air which is sent to the mill. 1he air

dries the coal in the mill as the coal is getting pulveriBed$ transports the accepted

coal particles to the furnace$ and supplies oxygen for the comustion of volatiles.

1he secondary air otherwise also known as auxiliary air helps complete

comustion.

1he pressure variation in air and gas path is shown in following diag.


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'ressure >ariation

Pressure Variatio i Air & Gas Pat! at "u## Loa$

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

3000

1 2 3 4 5 6 7 8 9 1 0 11 12

Pat! E#e%et

Pressure

&Pa'

(a#)u#ate$ 21* MW' Desi+ 210 MW'

Duct%D %an Duct (C#') #') Duct


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%uel air supplied around the air noBBle$ is 5uantity and velocity can influence the

flame front greately. 1he fuel air dampers controlling its velocity and its relative

5uantity w.r.t. aux. can e ad8usted to keep the flame front +mm away from the

fuel noBBles to keep it ade5uately cool at /c.

# fuel air auxiliary air ratio of 09? or 0/9// has een found more suitale than

earlier adopted ratio of *9 or +9@ for etter performance and slag free

furnace operation.


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"pening up the fuel air dampers or closing down the auxiliary dampers increases

the air flow around the fuel noBBles. Closing down the fuel air dampers or

opening the auxiliary dampers decreases the air flow around the fuel noBBles.

1he correct proportioning of secondary air etween the fuel compartment and

auxiliary compartment depends on the urning characteristics of the fuel. It

influences the degree of mixing the rapidity of comustion and the flame within

the furnace.

Fuel air da:


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"u>iliar, air da:


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4 %+E*"TI%$ %F &I$.B% "M+E*S

#ll auxiliary air dampers shall e open for oiler purge to ensure uniform purge.

#ll windox dampers except non-operating fuel air dampers shall modulate to

maintain,/ to +@mm. differential pressure etween windox and furnace up to

+= oiler load to keep proper air distriution around operating fuel noBBles.

#ll operating elevations of air dampers and their ad8acent auxiliary air dampers

shall modulate to maintain , to ,/mm :as specified; windox to furnace

differential pressure on full load.

1he primary air pulveriBed coal noBBles admit fuel at almost a fixed velocity of *@

mAsec$ over an elevation load range of / to ,=. 'rimary air flow through mill

has to e reduced corresponding to a velocity of not less than * mAsec. in p.f.

pipe to ensure stale flame at low loads.

1he fuel air :%.#.; supplying %.#. around primary noBBles shall e ad8usted to get

a stale flame aout +mm outside the noBBles.

More fuel air shifts the flame front further away and makes the flame unstale and

conse5uently haBardous situation develop.

Low fuel air results in urning within the noBBles and hence overheating and

detoroation of the noBBles and the conse5uent detoriation of the comustion

process and even impingement of flame leading to failure of the oiler tuing$ the

life of oiler noBBles is also consideraly reduced.

Large 5uantity of fuel air i.e. 0 to 0/= secondary air as against * to +=

secondary air sent around the fuel noBBles has helped to improve the urner

performance and solve slagging condition in the furnace.

More air is forced to flow through fuel air noBBles y opening the fuel air damoers

more and simultaneously closing in the auxiliary air dampers.

#fter += oiler load the auxiliary air dampers ad8acent to operating fuel noBBles

may e opened gradually to hold maximum wind ox to furnace over ?= to

,= oiler load range instead of ramping up the differential presuure at +=

oiler load :to ensure smooth operation and otain etter performance;.


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74 +*%UCTS %F C%MBUSTI%$ S!STEM

LetEs first see details aout the fuel i.e. coal to know the comustion products.

T,alue @? Hcal A Hg

*; 7ituminous Coal9 It is a road class of coal containing 0?= to ?= of fixed

caron y mass and *= to 0= y mass of >olatile Matter. Its calorific value ranges

etween ? HcalAkg to Hcal A kg. the coal is easily comustile and is most

suitale for comustion in pulveriBed form.

+; (u 7ituminous Coal9 1his is a class of coal that has lower heating value than

that of ituminous coal. Its C.>. ranges etween 0/ to ?0 Hcal A kg. 1his coal is also

suitale for comustion in pulveriBed form. %ixed Caron ranges etween 0= to /=$>olatile matter ranges etween *= to +=.

0; Lignite9 It is the lowest grade of coal. It is rown in color and remnants of

wood fiers are visile in this coal. It originates from resin rich plants and hence contains

very high inherent moisture :+=; and volatile matter. Its heating value is +/ HcalA Hg

to 0? HcalA kg

/; 'eat 9 It is not an I(1M coal. It is considered as the first step in coal formation.

It contains decomposed organic matter and minerals and J= moisture. It is not useful

for 'ower generation. 7ut due to its aundance in some countries$ it is used for heating

and in some other industries In India$ coal is graded as per its calorific value. Different


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Car;on ;urnt to Car;on i %>ide4

(ustance9 C G "* K C"*

#tomic or molecular weight9 ,* G +* K 00

ide4

(ustance9 *C G "* K * C"

#tomic or molecular weight9 *0 G +* K /?

ide ;urnt to Car;on i %>ide

(ustance9 *C" G "* K * C"*

#tomic or molecular weight9 /? G +* K


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T1eoretical air re?uire:ents for co:;ustion4%or supplying , Hg of "xygen$ :,A *+.,/; Hg i.e. 0.+* Hg of air is re5uired. (ince , Hg

of caron re5uires *.?@ kg of "xygen$ air re5uired will e *.?@ 0.+* K ,,./+ Hg of air.

#ir re5uirements for comustion of other constituents is also given y9

Hg of air re5uired K ,,./+ C G +0./?:) - ,A "; G 0.+* (


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In s1ort4 +roducts of Co:;ustion S,ste:

1his su-system should e capale of removing furnace gases over the entire

operating range of fuel urning system while maintaining the furnace pressure

within design limitations. # primary function is to remove inert comustion

product so that the furnace fuel air input can e continuously and immediately

ignited. Controls are provided for the operation of dampers in the flue gas system.

#lso the analysis of C"*$ o* and co in the product of comustion is very valuale in

determining the comustion efficiency and air infiltration. 1here is no perfectly reliale

means of measuring the air actually admitted to the furnace and the only means of

determining the amount of such air is from the analysis of products of the comustion

called flue gas.


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4 I$ST*UME$T"TI%$ L%'ICS F%* raft control 6

&ind.;o> +*ESS C%$T*%L

Draught Control


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Check the furnace to


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air entering from furnace ottom results in lesser hot airflow through air heaters

therey affecting oiler efficiency. #ir entering after comustion completion i.e.

from penthouse roof$ second pass expansion 8oints and from ducts upstream air

heaters$ shall account for the difference in "* level etween the furnace exit and

economiBer exit. #irflow control is ased on "* measurement at air heater inlet in

coal-fired oilers. %or a specified level of "*$ any air ingress efore this section

would result in reduced level of "* actually taking part in comustion in the

furnace$ therey increasing the unurnt caron and caron monoxide levels.

/. %ailure of %uel air dampers.


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Check that no override commands are present.

Check that the reference input : e.g '# flow; is "H.

Check the damper operation in manual.

1une the parameters to suit the firing regime.

94 C%$CLUSI%$

%or proper operation of windox oxygen measurement plays

ma8or role$ so it should proper.

egularly checking of furnace air leakages is necessary.

(ome new installation should prefer to reduce the losses and

increase the efficiency.

3AInstallation %f Fa;ric E>


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*. %aric expansion ellow provided from outside the wind ox to cover metallic

expansion ellow.

+. %aric expansion ellow provided at #') outlet duct in primary & secondary

metallic expansion ellow.

0. Investment of s. ,*.+0 Lakhs nergy (aving s. ,,* .,* LakhsAyear.

I:


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firing system4

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