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8/6/2019 Descon Presentation on Co-Generation 13-07-2010
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DESCONEngineeringLimited
SeminaratJuly2010
1
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Cogenerationis:
Ahighlyefficientmeans
ofgeneratingheatandelectric
Atthesametime
Fromthesameenergysource.
Productionofheatandelectricseparated
2
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en ra owergenera on
Simplecycleplant Combined
cycle
plantwithdieselengines Combined
cycle
plantwithgasturbines
E E E
E E
c ency c ency c ency
60%ofheat
dum ed in
condenser3
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Co
generation
Combinedc cle lant Combinedc cle lant
withdieselengines withgasturbines
EProcess
steam
E
E
E
E
Process
steam
Process
steam
Cond.return Cond.return Cond.return
Byi.e.extracting 50%process
steam30%ofheatwillbe
4
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Co
generation
without
condensing
Efficiencyofsystemcanbeincreasedinfarextendbydeletionof
.
Highheatlossesincondenserareeliminated
Process
steam
Process
steamE E Process
steam
Cond.return Cond.return Cond.return
Efficiencyofpowergeneration85till93%5
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Inco enerations stems withcombinedc cles
EfficiencycanbeincreasedfurtherbyadditionalfiringinHRSG
E E
fuel fuel
Process
steam
E E Process
steam
Cond.return Cond.return
Efficiencyofpowergeneratedbyadditionalfiringis100
till120%
6
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Effectofcogenerationonplantefficiency
How
Moreprocesssteamrequiredinrelationtoelectric
powerresultinhigherplantefficiency 7
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Cogenerationsystemswithoutsteamturbine
Process Process
10barE E
10
bar
Con .return Con .return
Howeverhighefficiencyis
notalwayseconomic.
Inco enerations stems
deletionofsteamturbine
andalowpressureboiler
.
specialinsmallerunits 8
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Impactofboilerpressure
on
power
output
in
co
generation
plants100bar/539
37%more
120
E 100t/h,
power
80
100
Processsteam
2barg,143C
30%more
power60Pressure
(Bar)Cond.Returnwith125C
45bar/430C
ar
17%more
power40
fuel
00 2000 4000 6000
E Process
steam
100t/h,2barg,143C
AdditionalPower(KW)withefficiencyofapprox86%
forbiomass/coaland94%forgasfiredCond.
Return
125
C 9
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Sameappliesalsowhenmoreandmorepowerisgeneratedin
combinationofbackpressureandcondensingsteamturbine
EE E
E
E50t/h 50t/h
Process 50t/h, Process 50t/h,
s eamCond.Return50t h arg, s eamCond.Return50t h arg,
10
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4300 Power(Kw)Incombinedcycleswithonlypowergenerationitisdifferent.
4239
4253
4228
4250
Additional
Power(KW)
45 Bar/66 Bar/
449C500C
41604150
30 Bar/
400C
428C 85 Bar/449C
E
4053
4050
4100
4000
0 20 40 60 80 100Pressure (Bar)
ar
WhenGTexhausttem erature500Cthena ressurebetween
30and45barwouldbeoptimal.
Howlowerthistemperaturehowlowerthepressure.
.
Forlargegasturbinesdoubleortriplepressuresaremore
economic. 11
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Impactofsteamtemperature
insimplecyclecogenerationplants
EEThisprocesssteamshould
10t/h.
Shouldbe10Coverheated.
Process
steamCond.Return
100t/h,
2barg,143C
ThereforetakeHPsteam
temperaturehighenough.
. .
At45barmin.430C
At66barmin.486C
t arm n.
At100barmin.539C 12
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HigherHPsteamtemperaturewillgivemoreoutput
. .
resultin0,8% morepoweroutput(byfiringadditionalfuelwith
efficiencyof86%).
W en u con ensingresu tin2% y iringa itiona ue wit
efficiencyof30till35%).
EEHoweverhighertemperatures10t hmeans
Selectionofhigheralloy/more
Process
steamCond.Return
100t/h,
2barg,143C
Isthiseconomic?
13
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Feedwaterpreheating
Whenonl
rocess
steam
su l
:HowmuchmoreEpowerincaseofpreheating
with addingadditionalfuel:
E2estage:
At100bar4,7%more
Processsteam
2barg,143C
At65 ar 2,9 more
Withefficiencyofapprox45%onfuelinput.
Cond.Returnwith125C
Economic?
es age:At100bar5,8%more
At65bar 5,4%more
Withefficiencyofapprox52%onfuelinput. 14
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Whennoprocesssteamsupply/onlycondensing:
without addingadditionalfuel:
E2estage:
At65bar 0,6% more
Economic?
1estage:
At100bar2%more
At65bar1 7%more
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Effectcogenerationonsteamturbineselection
Backpressurecontrolfor
controllingLPsteampressure
HPsteampressurecontrol
bysteamturbine
E
ofapprox10%ofdesignflow.
NOTE:
Steamturbinesshouldbeselected
ver accurate.
Process
steamCond.Return
100t/h,
2barg,143C
Thenormalandmaximumsteam
flowshouldnotdeviatemuch.
turbine.
Speciallyforcondensingpart. 16
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Eachsystemisuniqueinsteamandelectric
requirement.
forthemosteconomic solution.
1. Whatarethemaximum,normalandminimum
steamandpowerrequirements.
2. Whataretheo eratin times3. Whatshouldbetheavailability
4. Donotusesteamturbinedrivenequipment
thenwiththepowergeneratingequipment.
5. Useelectricdrivenequipment.
6. Forlargepowerconsumersusevariablespeed
controldrives. 17
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Boilerwaterandsteam requirements
Availabilityoftheplantdependshowthewaterandsteam
conditionsaremaintained.
It
is
recommended
to
use
demi
water
as
make
up
and
to
polish
thereturncondensatewhenits qualityisnotguaranteed.
Thedosingofchemicalsinthefeedanddrumwatershouldbe
controlledautomaticallytoensurecompliance.In ineinstrumentationisrequire tomaintaint erequire
qualitieswithinacertainband.
Maintenanceofsystemisessential.
ALabisneededtocollectdailyasamplestochecktheaccuracyof
.
Thechemicalsshouldbesuppliedbyreliablesuppliers. 18
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BiomassFuelsinPakistan
1. Bagasse
2. SugarcaneTrashAllthosefuelshavecommon:
HighVolatilecontent. ornco s
4. Ricehusks5. CottonStalks
NettHeatingvalue onbasisofashand
waterfreeallapproxthesame(17,8till
19MJ k6. Wheatstraw
7. WheatriceNOTE: Thecompositioncanvaryper
seasonandperarea.
Fuelsaredifferentin:
moisturecontent
Ashcontent
foranalysis
Thefuelscanbefiredondifferent
Alkalicontentinash Sulfur
sto ertypesan n u ze e
system.
density19
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Localcoal
KnownanalysisofminesinMakarwal Areaonly
ItisahighvolatileBbituminouscoal
Moisturecontent5till10%
Thesulfurcontentisveryhigh7,1wt%ondry.
s con en var es rom
Theinitialdeformationtemperatureisunknown(firstmeltingpoint
ofelementsinash .
Softeningtemperatureis1020C
Thequalityofcoalisnotconsistent
Thecoalsuppliedneedstobeanalyzedbeforefiringit. Duetohighersulfurcontentandexpectedvariationinashcontent
.
Tohandlethevarietyincompositionwerecommendabubblingfluidizedbed
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Im rt c al
Hi h ualit coalissu liedfromIndonesia SouthAfricaand
China ItisahighvolatileAbituminouscoal
Moisturecontent10till 20%
ashcontent5till15%
w u u , ,
Highinitialdeformationtemperature,above1200C.
.
23
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Characteristicsofbiomassandcoal
52
50.0
.
30
25 29
18 18.5 1620.0
30.0
.
8.4 811
5.71011
13
712
4.4
11.7
2 2.5
8 7.0
0.0
10.0
MoistureContent% LHV(MJ/Kg) Ash
24
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Pric f i ma an l cal c al r k an r MJ
Pricesaremostl relatedtowei ht
Howevermorerealisticistorelatetoenergyonlowerheatingvalue(LHV).
Thepropertiesofbiomassfuelcandifferperareaandyear.It
isimportanttoverifythepropertiesofbiomassbyaproper
test rocedure.
Thesameappliesforlocalcoal
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PricesofBiomass&Coal
r ce s g0.37
0.300.35
0.40
r ce s
5.36.0
8.0
10.0
.
0.21 0.19
.
0.15
0.200.25
.
34
2
0.0
2.0
4.0
0.00
0.05
0.10
Price(Rs/Kg) Price(Rs/MJ)
Thelocalcoalisver com etitiveinrelationtobiomassfuels.
Asbiomassfuelsareenvironmentfriendly theyneedmorestimulation.
i.e.carboncredits,positiveeffectontaxes,etc. 26
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Eff ct f f l n l i tic
Com aredtocoalbiomasshaslowerdensit .
Morevolumetohandleintransport,storageandfeedingsystem.
Biomassisnotphysicallyhomogeneousandfreeflowing.
Difficultiesintransportation,metering,storageandfeeding
.
easiestonestodecompose.ItcanreducetohalfitLHVvalue
withinoneyearofstorage.
27
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Effectonfuelhandlingforsolidfuels
20,336
23,780
20,000
25,000
LHV(MJ/M)
10,000
15,000
2,3091,302
2,5991,526
2,9541,615 2,098
0
5,000
28
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Effectoffuelonashhandling
16.00
18.00
s con en g )
12.00
14.00
6.00
8.00
10.00
2.00
4.00
0.00
29
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Envir nm nt BiomassisarenewableenergywhichdoesnotincreasetheCO2level. CO2
creditswillgiveacostsaving
Duetohighvolatilecontent theNOx levelswithbiomassfiringarelow
.
Sulfuremissionsarenil.Localcoalhashighsulfurcontentandrequirefluidized
bedcombustionwithlimestoneinjectiontokeepSoxemissionlow.
Sulfurdioxideemissionrequirementforfossilfiredboilersisunclear.
For
oca
coa
imestone
as
to
e
injecte
in
e
or
in ing
t e
su ur.
Norma y
80%ofsulfurisbondedwithlimestoneThiswillincreasethetotalashcontentwithapprox 60%.
Therequirementoflimestonemakesthelocalcoalapprox15%higherinprice.
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Fuelsaredifferentin:
A. moisturecontentWhatarethe
effectsonselection.
C. Sulfur
D. Chloride
offiringandboiler
system?
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A.Moisturecontent
Highmoisturemeansthatthewaterhavetobeevaporatedfirst.
Thisrequirespreheatedairsupply.Thisrequiresanairpreheateratoutletof
boiler.
i.e.Bagasse of52%moisturecontentrequires220till260Cairtemperature.
Incaseoflowmoisturecontenttheairpreheatingshouldbelimitedinorderto
avoid
overheating
of
stoker
system.
Howhigherthemoisturecontenthow lowertheboilerefficiency
causesmoreerosion.
LowermoisturecontentinBa asse from50to40%resultsina rox1,8%hi her
efficiencyand15%lessfluegasvelocities.
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B.Ashcontent
Whenlowashcontentof2till4%andhighvolatilebiomass
fuelsareusedthenastationarystokertypecanbeused.Also
Steamnozzlesforcleaningthe
grate
Castironelements
attachedandcooledbythe
Watercooledtubesas
tubes
partofboilersystem
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Dumpinggrateisnotrecommendedasitwillgive:
an nterrupt on nsteamsupp y ur ngc ean ng muchhigher unburnedlosses
moreinterruptionsduetooverheatingofgratebars
Inothercaseswithashcontentsupto20%atravellinggrateis
recommended.
34
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Howhighertheashcontenthowmoreerosionintheboiler.
pec a yw ens cacontent svery g .
Howhighertheashcontenthowlargertheboilerwillbe.
Ricehuskshasextremely highsilicacontent of96%andsuffer
banks.
The
allowable
velocities
are
more
then
50%
less
then
for
other
omass ue san coa . sresu s namuc arger o er en
normallyseenforotherkindoffuels.
Furtheratravellinggratewillhavealsoahighwearandteardue
tothisash.
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Asthericehuskwillbefiredmainlyin
furnacemainlyasflyashawatercooled
inclinedgrate systemisverysuitable.
Thegrateisthenprotectedfromoverfiring
bythewatercooledgratesystem.This rateisnormall usedforaver wide
rangeoffuelsandlowashcontents.
Theashofricehusksistransformingfromamorphousstateto
crystallinestatewhenitisexposedtotemperaturesabove850
. .
Theashcanthenbeeasilyusedinsteelmillsandother
applications.
t a u ze e systemt ewearan earpro em s
minimized.36
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travellingorvibratinggrate.
emax mumamoun o coa s oweverres r c e .
Whenthiswouldbetoohighthelocalfiringtemperaturesget
toohighandtheashofthebagasse wouldclinkerandcause
problemsonthegrateandfoulinginfurnaceandheating
Withtheotherfuelmixturessimilarlimitationsarethere.
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C.Chlorine,sulfurandashcharacteristics
Theashcharacteristicsoffuelsareimportant.
Speciallyimportantare:
thealkalimetals(Ca,Na,K)areimportant.
Further
the
sulfur
and
Chlorine
content
in
the
fuel
is
an
important actor
Thosecontentsneedstobeverifiedinthelabbeforedeciding
thebestcombustionandboilersystem.
38
El i bi & l i ll
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Elementsinbiomass&coalpotentially
.7.1
7.00
8.00
4.005.00
6.00
0.60
0.20.02 0.1 0.03
0.3 0.2
0.80.50 0.4
0.2 0.1 0.01
0.70.5
1.47 1.47
0.73
0.32 0.18
2.442.22
0.12 0.09
0.00
1.00
2.00
.
Sulphur(S)%
K+Na%
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Thoseelementsdeterminetheclinkering,slagging
andfoulingandalsotheerosionandcorrosion
potentialsofthefuels.
Arangeofindicesareavailabletoassistinpredicting
thosepotentials.
Alsotestarerequiredtodeterminethefollowing
conditions inthelab oftheashathightemperatures:
initialdeformationtemperature
sinterin tem erature
hemisphericaltemperature Flowtemperature
Thosetestswillalsoassistinpredictingthe
clinkering,slagging andfoulingpotentialofthefuels 40
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Thepotasium (K)salts(KCl andKOH)becomevolatileabove
650Canddepositiondownstreamcancauseserious
corrosionandfouling.
For that reason the flue asses will be cooled down in water
cooledcavitiestill650C whentheindicesindicatesthis
potentialproblem.
Werecommendtofirefuelswithhigh(Ca,Na,K)contentsin
afluidizedbedsystemasthecombustiontemperatureinthebedandfreeboardarelowandcanbecontrolledmore.
Thebiomassfuelsare:
cottonstalks
sugarcanetrash corncobs
Thosecanbefiredincombinationwiththelocalcoal. 41
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Theratioof sulfurtochlorineindicatesifcorrosioncanbe
expectedinthesuperheaters.IfChlorineismuchhigherin
contentthenthesuperheater tubemetaltemperature
needs to be ke t low maximum 450 C .
Orinconel tubesshouldbeusedwhenhighersteam
temperaturesarerequired.
Thesulfurcontentisalsoanindicationforthesulfur
dewpoint ofthefluegasses.Thewaterinlettemperatureofeconomiser andalsothetubemetaltemperatureoftheair
preheatershouldbekeptabovethistemperatureinorder
toavoidsulfurcorrosion.
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Inordertooptimizethefiringprocess
furnacecorrectly.
mpor an ac orsare:
furnaceliberationrate
ExcessairAmountofundergrateandoverfiring
airamounts
Correctinstallationofoverfiring
system
es ence me
Furnacefluegasoutlettemperature43
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Allthosefactorswilldeterminetheunburnedcontentat
.
Theflyashshouldnotbesticky atoutletoffurnaceinorder
toavoid heavyfoulingofthesuperheaterarea
Thetubesintheboilerconvectionsectionwillbearran ed
inlineandinbetweenthetubessufficientdistance willbe
keptinordertominimizethefouling.
Byadequatesteamsootblowingthesurfaceswillbekept
clean.
Thedustcollectedinthehoppersandcyclones'willbere
injectedinthefurnaceonseveralpointsjustabovethe
grateintothefurnacetolowertheunburnedto50%.
45
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So,beaware:
Fordesigningthemostappropriatefiringandboiler
systemtherangeoffuelshavetobedeterminedin
advanceandlabtestshouldbemadeavailable.
Thenwecansu l as stemwhichwillbein
compliancewithyourrequirementsinsteamand
powersupply,availabilityandreliabilityofthesystem.
Forensuringhighefficiencies,reliabilityandthe
capabilitytofirealargerangeofbiomassandcoalfor
its
life
time
we
recommend
abubblingfluidizedbed
system.
ThankYouForYourAttention
46