InNovember,2007,BjerringbroVarmeværkcoulddemonstrate
that reality surpassed the first calculations. By installing an
absorptionheatpumpinoneofBjerringbroVarmeværk’sfour
gasengines,there isnowanextraheateffectof0.9MWat
disposal-andthatiswithoutusingmorenaturalgas.
Previously,thefluegasfromtheenginewascooledfrom428°C
to63°Cindistrictheatexchangersbeforeitwasledoutdi-
rectlythroughthechimney.Inanewfluegasexchangercon-
nectedtotheheatpumpevaporator,afurthercoolingto27°C
and condensing of the flue gas vapour take place. The heat
pumpabsorberandcondenserarecooledbydistrictheating
water,whichisherebyheatedfromabout40°Cto80°C.That
isabovetheoperationtemperaturesinBjerringbro’sdistrict
heatingnetwork,andthusthereisnoneedforcoolingofheat
fromtheheatpump,whichisusingtheevaporationheatfrom
thefluegaswithoutlosses.Condensingoffluegashasbeen
consideredbefore,butthenetworkreturntemperatureisnot
lowenough.
HIGHER DEGREE OF EFFICIENCY
Before the renovation the heat efficiency was 48.4%. With
theextraoutputof0.9MW,theheatefficiencyhasincreased
to 60.1% while the electricity efficiency remains unchanged
42.1%. The total efficiency of the plant has thus increased
from90.5%to102.2%. Inotherwords,an increase ineffect
EFFICIENCY IMPROVEMENT
If somebody believes that district heating is old technology
withoutsignificantperspectives,theyshouldturntheireyesto
Bjerringbroheatingplant.Here,theyhavesucceededinutilis-
ingtheenergyfarmoreefficientlybyusingknowntechnology
inacompletelynewway.Theresult isthatexpensivenatural
gas is saved, and that at the same time CO2 emissions are
reducedby1,350tonsperyear.Andtheinvestment?Itisex-
pectedtobepaidbackwithintwoyears!
ItallstartedwithBjerringbroVarmeværkhavingto invest in
newequipment.Agasboilerwasripeforreplacement.How-
ever,withincreasingpricesofnaturalgas,therewasaninter-
estinfindingsomethingmoreefficientthan justbuyinganew
naturalgasboiler.
Onepossibilitywastocondensethefluegasfromtheengine
by means of electricity, but that was not interesting due to
the electricity taxes. If, however, the flue gas could be used
forpoweringaheatpump,thatwouldbeaninterestingpos-
sibility.
0.9 MW ExTRA
During2006itwasclearthatThermaxcouldsupplyasuitable
absorptionheatpump,anditwasdecidedtoinstallapumpon
oneoftheengines.
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totalutiliZationoF eneRgyin BjeRRingBRo
ByCharlesW.Hansen,ProductionManager,BjerringbroVarmeværkAmba,BjarneChristensen,SalesEngineer,HollensenEnergiA/Sand
NielsOttoClausen,ProjectManager,COWIA/S
New heat pump at the CPH plant in bjer-
ringbro utilizes the heat in the flue gas
and thus increases the plant’s heat effect
without increased use of natural gas.
E N E R G Y A N D E N V I R O N M E N T
from3.7MWto4.6MWhasbeenobtainedwithoutcausingad-
ditionalconsumptionofnaturalgas.However,thecondensed
vapourfromthefluegasmustbedischargedaswastewater,
implyingadischargeduty.
Aconsequenceoftheconversionofsofaroneengineisthat
thedistrictheatingflowtemperaturehasbeenreducedfrom
max.90°Cto80°C.Thismeansthatthecapacityoftheplant’s
heatstoragetankisreducedcorrespondingly-totheextent
thattheheatissuppliedfromthereconstructedplantalone.
Therefore,BjerringbroVarmeværk isnowconsideringestab-
lishmentofanotherheatstoragetankinordertomaintainthe
fullcapacity.
THE ACTION PLAN IS CONTINuOuSLY REVISED
Thefirstideasofusingaheatpumpforincreasedutilisationof
theheatinfluegasdevelopedinconnectionwithpreparation
oftheBjerringbroVarmeværk’sactionplan inOctober2005.
Theplanhassubsequentlybeenrevisedseveraltimes.
Forthetimebeing,theextraheatstoragetankisbeingcon-
sidered,asthis isthepreconditionfor itbeingprofitable in-
stallingfluegascoolingatanotheroftheCPHplant’sfour18-
cylinderlean-burnenginesfromRolls-Royce/Ullstein.
Because,evenifthemarginalpricehasdecreasedby100DKK
(approx.14Euro)forthereconstructedengine,theremustbe
capacitytostoretheheatproducedwhentheelectricityprice
ishigh.
Whetherthethirdandthefourthenginearetobeequipped
withheatpumpssomeday isdependingonBjerringbro’s fu-
ture heat requirement and on the number of working hours
expectedfortheindividualengines.
Inanycase,anactionplanisagoodtooltoestimatethefuture
investments.
Thetestoperationhasdemonstratedthattheplanthasthe
expectedoutput.Therefore,theheateffectoftheCPHplant
canbeincreasedbyfurther3x0.9MWwithoutincreasedcon-
sumptionofnaturalgas.
InNovember2007,theplanthasdefinitivelybeentakenoverby
Bjerringbroheatingplant,whichcarriedouttheprojectinco-
operationwithHollensenEnergyA/SandCOWI.Thermaxhas
suppliedtheabsorptioncoolingplant.Theinvestmentinheat
pump,buildingandinstallationamountstoabout6millionDKK
(approx.0.8millionEuro).
POSSIbILITY OF DISTRICT COOLING
AnotherpossibilityofusingabsorptioncoolingplantsatCHP
plantsisproductionofdistrictcooling,whichalsoisincludedin
BjerringbroVarmeværk’sactionplan.
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11
E N G I N E E R D E L I V E RD E S I G NL I S T E N
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APVPlatinvej 8
DK-6000 Kolding T: +45 70 278 444F: +45 70 278 445
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APV Annonce.indd 2 29/11/07 7:27:39
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total utiliZation oF eneRgy in BjeRRingBRo
Bydistrictcooling,thedistributiongridwillbesuppliedfrom
theevaporatorwithasupplytemperatureof6°Candareturn
temperatureof14°C,whilethefluegasisonlycooledto63°C.
Inthatcase, itwillbenecessarytocoolsomeofthesurplus
heatinacoolingtower.
TheCOPofsuchaplantwillbeabout3 (CoefficientOfPer-
formanceisthecoolingpowerandthesuppliedheat-orelec-
tricitypowerratio).
Forcomparison,COPforanabsorptioncoolingplantoperated
by hot water is about 0.7, whereas a traditional compressor
planthasaCOPofabout5.Inthelattercase,itmustbetaken
intoconsiderationthatthedrivingenergyiselectricity,which
involvesconversionlosses.
Seeninthatlight,thepossibilityofdistrictcoolingispromising.
Layout of the plant with the absorption heat pump causing an
increase in the total efficiency from 90.5% to 102.2%.
BEFORE NOW
Fluegastemperatureinchimney 63°C 27°C
Electricityefficiency 42.1% 42.1%
Heatefficiency 48.4% 60.1%
Totalefficiency 90.5% 102.2%
Thermaloutput 3.7MW 4.6MW
Overviewofoutputandefficiencybeforeandafterinstallation
oftheabsorptionheatpump.
Forfurtherinformationpleasecontact:
BjerringbroVarmeværkA.m.b.a.
Att.:Mr.CharlesWintherHansen
Realskolevej18
DK-8850Bjerringbro
Phone:+4586681422
COWIA/S
Att.:Mr.NielsOttoClausen
JensChr.Skousvej9
DK-8000ÅrhusC.
Phone:+4587396712
HollensenEnergyA/S
Att.:Mr.BjarneChristensen
Drejervej22
DK-7451Sunds
Phone:+4597142022
Thehotexhaustgasisledthroughtheengine’sgenera-
tor,whichcontainsamixtureofwaterandlithiumbro-
mide(LiBr),approx.58%LiBr. Inthegenerator,enough
heatisaddedfromtheexhaustgastomakethesolution
boil,andthewaterisledoutassteam.Theconcentrated
LiBr solution, ca. 62%, returns to the absorber of the
engineviaacounterflowheatexchanger.
Thesteamfromthegenerator iscondensed inacon-
denserandflowsviaaheatexchanger,whichcoolsthe
80°C hot condensate with the return water from the
districtheating,backtotheevaporator.
From the evaporator, the water is pumped via trickle
tubes out over the evaporator tubes. Thus the water
evaporates,absorbingthenecessaryevaporationheat
fromtheevaporatortubes,asthepressureintheevap-
orator corresponds to the desired evaporation tem-
perature.
The evaporated water passes a tower with absorber
tubes,whichmakesthesteamcondenseagain,andthe
evaporationheatisdeliveredascondensationheat.The
condensate/wateristhenabsorbedbytheintenseLiBr
solutionfromthegenerator,whichhasflowntotheab-
sorber.ThenowdilutedLiBrsolutionofapprox.58%is
pumpedbackintothegenerator,andtheprocesscycle
isfinished.
What is used for district heating is the cold water in
theevaporatorcirclecondensingalargeamountofthe
steam intheengine’sfluegas inaheatexchangerfor
thepurpose.Atthesametime,thefluegasiscooledto
about27°C,andtheheatthusabsorbedbytheevapora-
torcircleisreleasedintheabsorptioncoolerviatheab-
sorberandanumberofinternalheatexchangers,which
a.o.alsoreusethecondensingheatfromthewater in
thecircle.
Thethermaloutputfroman18-cylinderUllsteinBergen/
Rolls Royce motor has thus increased by in total 888
kWhperoperationhour,correspondingtothethermal
efficiencyhavingincreasedby11.7%.
E N E R G Y A N D E N V I R O N M E N T
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