TEAM – C&I
INTRODUCTION The total combustion air flow supplied in the boiler consists of two parts 1
The primar primary y air, air, which which is used used for drying drying and transp transport orting ing the coal coal from the pulveriser through the coal piping into the furnace furnace and is supplied by the primary air fans
2
The secondary air sent through the four corners of the wind box and is supplied by the FD fans. The The tota totall seco second ndar ary y air air flow flow is con contr trol olle led d by for force ced d draf draftt fan, fan, in in proportion to the fuel being fired. Total air secondary flow is measured by a flow metering devices called aerofoil meter. The measur measured ed air flow flow is is compa compared red agains againstt the the fuel fuel flow flow,, with with the resultant signal positioning the FD fan inlet guide. This inlet guide is positioned to maintain the re"uired air flow regardless and #ndependent of secondary air damper position The secondary air dampers located in wind box apportions the total
3
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secondary air between various elevations.%ow this air is proportioned, depends on which fuel is being burnt, the number of elevations in service and the firing rate at each elevation
The function of Secondary Air Damper Control System (SADC) is to proportion the total secondary air around the firing elevation as per the amount of fuel fired and the no. of firing elevations e levations decide the damper position BASIC DESCRIPTION & TERMINIOLOGY #n total, each wind box assembly is divided into 13 compartments. &ach compartment is designated either by single or double alphabet constit uting 13 elevations. 'n elevation elevation designates all the four corner compartments.There are ( elevations which houses coal no))les for firing the main fuel. These are designated with single &nglish letter *'+ through *F+.
There are ! elevations which houses oil burner assembly for firing start up stabili)ing fuel vi).. -ight Fuel il %eavy fuel oil /-F0. These are designated designate d as ', D &F. 4% &ach oil compartment is interposed between two coal ompartments.
There are two nos. of over fire air compartment at the top of the windbox. They are designated as F' - /ver fire air -ower0 and F'5 / ver fire air
At the inlet of each compartment compartment there are control dampers. dampers. Each damper damper is operated by a damper damper drive unit. All damper drives in any one elevation receive the same sinal from the secondary air control system. If secondary air is admitted to a fuel compartment in service! it is referred as fuel air. "econdary air is admitted to the furnace throuh air compartments and fuel compartments not in service! is termed as au#iliary air. The au#iliary air damper control is separate from the fuel air damper control
CONTROL PHILOSOPHY The au#iliary air damper control system positions the au#iliary air dampers to maintain a $ind bo# to furnace differential pressure . The au#iliary air dampers are positioned to maintain the re%uired $ind bo# to furnace differential pressure accordin to the boiler load. The fuel firin rate
air damper
control system positions the fuel air damper in proportion to the fuel
This unit is e%uipped $ith oil elevation for $arm up and stabilisation &desined for '() *(+ ,CR-. In this case the oil elevation dampers are positioned to a fi#ed + openin durin oil firin. hen oil is not fired! these dampers are controlled to maintain the $ind bo# to furnace differential pressure in line $ith other au#iliary dampers .
Au#iliary air dampers dampers / All elevations elevations of the au#. au#. air dampers dampers $ill be automatically s$itched to 0,anual1 control and then commanded to
open '((+!
if any one
of the follo$in conditions e#ist. ' 2 3oth 4D fans are O44. 2 5 3oth ID fans are O44. O44. 2 * ,aster fuel fuel trip occurs. 2 6 7oss of unit critical po$er . &8569 DC Also the au#iliary au#iliary air control control loop is tripped to manual if any of the follo$in conditions e#ist. 2 ' D: transmitter deviation hih. 2 5 4ailure of selected D: transmitter 2 * 4urnace to indbo# D: very hih &; 56(mm C7-.
hen an elevation of main fuel is started! the associated fuel &coal - air dampers open and modulate as a function of feed rate . A fuel &coal- elevation is selected to be closed $hen the associated feeder is tripped .
The au#iliary elevation dampers act as fuel &oil- air dampers $hen oil firin is taacent pulverisers are off and 0No 3oiler Trip1 sinal is present.hen a ?4O Elevation is started &i.e. $hen the associated 0elevation bac<)up1 trip is removed- the associated au#iliary air dampers in that elevation are set t o preset position for ?4O firin.
The over fire air dampers are positioned as a function of the boiler load. The lo$er O4A dampers start openin at @( + boiler load and are fully open $hen the boiler load reaches @ +. The upper O4A dampers start openin at @ + boiler load and are fully open $hen the boiler load reaches '(( +
When the unit load exceeds !" o# MCR$ the #ollo%in e'ents occu(s )
When the Unit Load is increas increased ed ao!e "#$ MCR% the A'i(iar) air da*+ers on e(e!ation AB% BC% CD% DE% E,% ,G% G- & -- are c(osed in a ti*ed se.ence /0# seconds inter!a(1 +ro!ided the associated coa( e(e!ations are not in ser!ice and the associated oi( e(e!ations are not in ser!ice2 The a'i(iar) air da*+ers are c(osed% startin3 4ro* to+ise(e!ation% (o5est air When the Unitthe Load increased increas ed+ro3ressin3 ao!e "#$ to5ards MCR% thethe A'i(iar) e(e!ation2 da*+ers on e(e!ation AB% BC% CD% DE% E,% ,G% G- & -- are c(osed in a ti*ed se.ence /0# seconds inter!a(1 +ro!ided the associated coa( e(e!ations are not in ser!ice and the associated oi( e(e!ations are not in ser!ice2 The a'i(iar) air da*+ers are c(osed% startin3 4ro* the to+ e(e!ation% +ro3ressin3 to5ards the (o5est e(e!ation2
When the nit (oad is redced e(o5 "#$ o4 MCR% the 4o((o5in3 e!ents occr6 7 The 5ind8o' to 4rnace di9erentia( +ressre set +oint re!erts to its ori3ina( !a(e2 7 The a'i(iar) air da*+ers associated 5ith the coa( and LO e(e!ations not in ser!ice are o+ened in a ti*ed se.ence /0# second inter!a(1 startin3 at the (o5est e(e!ation% +ro3ressin3 to5ards the to+2 When a LO E(e!ation is started /i2e2 5hen the associated :e(e!ation ac;8+< tri+ is re*o!ed1 the associated a'i(iar) air da*+ers in that e(e!ation are set to +reset +osition 4or LO =rin32 When the :Post Tri+ Pr3e Ti*e E'+ired< co**and is esta(ished and a(( ,D > ID 4ans are not o9 and a Master 4e( tri+< co**and doesn?t e'ist% then a "@ seconds contin3 +eriod is started2 A4ter it e'+ires% the :O+en A(( A'i(iar) Air Da*+ers<
,COALAIRo4 .AMPERS CONTROL o+en 0##$*+EL 5hen an) one the 4o((o5in3 conditions e'ist2 7 A(( ,D 4ans are o9 7 A(( ID 4ans are o9 7 Master 4e( tri+ e'ists /4or *ore than seconds PULSE1 7 Loss o4 Unit DC +o5er When a coa( e(e!ation is in ser!ice% the associated 4e( air da*+ers *od(ate as a 4nction o4 4eeder s+eed as indicated ) the associated coa( e(e!ation :MODULATING< (i3ht co*in3 on2 When the coa( e(e!ation is i s sht do5n% the associated 4e( air da*+ers are c(osed% as indicated ) a :CLOSED< (i3ht 2 When the :Post Tri+ Pr3e Ti*e E'+ired< co**and is esta(ished and a(( ,D and ID 4ans are not o9 and a :Master 4e( tri+< co**and does not e'ist% the :O+en ++er 4e( air da*+ers /E(e!ation -% G% , & E1< co**and is re*o!ed 4ro* *e*or)2
ELE/ATION 0AC1+P ELE/ATION TRIP
LOGIC FOR CLOSING OF DAMPERS
! " COMMAN. 2 3! 4a45s 2 c6linde( is #ull o5en 2 #ull close o# da45e( E7E9ATION E7E9A TION A3 3ACBU: TRI:
MFT
OR
SET RESE
LOTV TRIP
GATE
LOSS OF 24 V DC
HOTV TRIP
T ON 6MIN
STOP COMMAN. *OR 0OTH 7& AN. 3&8
START COMMAN. *OR ANY PAIR ,7& OR 3&8 -
T
SADC POSITIONING
Modulation o# Auxilia(6 Ai( .a45e(s
POST P+R9E TRIP POST PURGE EFCURSION PROTECTION 68 Post +r3e e'crsion e'crsion +rotection circit has een desi3ned in the ,rnace ,rnace Sa4e3ard S+er!isor) S)ste*2 It o+erates as descried e(o56 When a(( the 4o((o5in3 conditions are satis=ed% a @8 *inte contin3 +eriod is started2 7 Li3ht oi( tri+ !a(!e c(osed2 7 A(( e(e!ation a(( LO no(e !a(!es c(osed2 7 A(( ,eeders o92 7 Air Ho5 "# $ MCR and J# $ MCR2 7 A(( scanners sho5 :no Ha*e<2 7 A(( -ot air 3ates c(osed2
POST P+R9E TRIP 7 A(( a'2 air da*+ers *od(atin3 7 A(( PA 4ans o92
A#te( : 4inute countin 5e(iod ex5i(es$ the ;Post Pu(e *an T(i5< 4e4o(6 is set$ i# 'e(6 hih o( 'e(6 lo% #u(nace 5(essu(e exists$ the 5ost 5u(e #an t(i5 co44and is issued ,#o( t(i55in *.&I. #ans-= When an6 LO 'al'e is o5en$ this is (eset2
Modulation o# *uel Ai( .a45e(s
Modulation o# O'e( *i(in Ai( .a45e(s
The t%o ele'ations o# the o'e( >(e ai( da45e(s %ill ?e auto4aticall6 s%itched to ;Manual< cont(ol and then co44anded to o5en 7!!"$ i# an6 one o# the #ollo%in conditions exist
Master 4e( tri+ occrs2 Loss o4 nit critica( +o5er 2/ DC1 Both ,D 4ans are O,,2 Both ID 4ans are O,,2 WB To ,rnace DP e'ceeds #** WCL2
O*A
SA in(et to the Wind Bo'
Wind 0ox S+ind(es o4 Pne*atic C)(inders% 5hich Re3(ate Secondar) Air Da*+ers
