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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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