15th North American Waste to Energy Conference May May 21-23, 2007, Miami, Florida USA NAWEC15-3201 Doubling the Energy Advantage of Waste-to-Energy: District Heating in the Northeast U.S. Priscilla Ulloa and Nickolas J. Themelis Earth Engineering Center and Department of Earth and Environmental Engineering, Columbia University, 500 West 120 th St., 918 Mudd, New York, NY 10027, USA (pau2102@columbia.edu) Abstract In District Heating (DH),alargenumberofbuildings are heated froma central source by conveying steam or hot waterthrougha network of insulated pipes. Waste-to-Energy (WTE) signifies the controlled combustion of municipal solid wastes to generate electricalandtheralenergyinapowerplant. Bothtechnologies havebeendevelopedsimultaneouslyandareusedwidelyinEurope. IntheUnitedStates,however,WTEisusedprincipallyforthegenerationofelectricity.TheadvantagesofdistrictheatingusingWTE plants are: overall fuelconservation, byincreasingthethermalefciencyofWTE, andoverallreductionofcarbon dioxide emissions to the atmosphere. The purpose ofthisstudywas to examinethecurrentsituationofdistrictheating inthe U.S . and determine the potentialfor applying DHto existingWTEplants. ApreliminaryevaluationwasconductedofDRapplicationattwoWTEfacilities in Connecticut: the Wheelabrator Bridgeport and the Covanta Preston facilities. Using a Canadian methodology, the minimal distributionheatingnetworkcostsfor Bridgeportwereestimatedat about$24 million dollarsforprovidingheatto asurroundingarea ofonesquaremileandtheDHrevenuesat$6.8million. Keywords: waste-to-energy,districtheating,combinedheatandpower,cogeneration,municipalsolidwastes Introduction DistrictHeatingisdefnedasthedistributionofthermal energyfomacentralsourcetoalargenumberofresidential, commercialandindustrialconsumersforuseinspaceheating, waterheatingandprocess heating.Thecentralsourcemaybe anoil-fedboiler,aWaste-to-Energy(WTE)plant,ortheby productsteamofautility. Thisapproach,alsocalled "cogeneration"or"combinedheatandpower(CRP)",hasa veryhighenergyutilizationeficiencythatcanreach80%. Therearesignifcantadvantagestobegainedfromaco generationWTEplant.First,theenergyefciencycanbe increasedbymeansof DHfrom 22%(electricityproduction only)to80%.Forexample,DanishWTEfacilitiesobtainan averageof0.6 MWhofelectricityand2 MWhofheatper metrictonneof MSW,thustriplingtheamountoftotalenergy obtainedfomMSW.Second,thehighefciency andlow emission levelsof WTEfacilitiesmakethemenvironmentally friendlysolutions,ascomparedtoothertechnologies. Currently,aconventionalWaste-to-EnergyplantintheU.S. losesovertwothirdsoftheenergyreleasedfromthe controlledcombustionofmunicipalsolidwastes(MSW).This energy isrejectedinthecondenserintheformoflow temperaturewaterthat isnotusedeffectively.Therefore,DH presentsWTEfacilitieswiththeopportunityto increase theral eficiency. However,therearesomechallengesthat 29 shouldbeaddressed.Forexample,itmaybenecessaryto modithesteamturbine andprovideequipmentinthefacility torecoverheatintheformofhotwater. Moreover,thethermal efciencyofelectricitygenerationwillbereducedsomewhat whenco-generatingheatandelectricity,thoughthetotal efciencywillincrease.Also, ittakes several yearsto buildan extensivedistrictheatingsystemand requireslong-term planning.Thirdly,DistrictHeating iscapital-intensiveand requiresvisionandcommitment. Thepurposeofthisstudyis(I) toexaminethecurrent situationofthe district heating intheU.S.and(2)topresent thetechnicaland economic aspectsofapplyingDHtoexisting WTEplantsintheUnitedStates.Thestudyexaminesthe retrofittingoftwoWTEfacilitiesinConnecticut.These facilitieswerechosenbecauseoftheirlocationinthe norheaster region,whereenergypricesandpopulation densityarerelativelyhighandencouragesuchaproject.The studypresentstheadvantagesanddisadvantagesofretrofitt ing these plantsto co-generate heatandelectricityandprovide DH totheirregion.Finally,thestudyprovidesaverypreliminary costanalysisofimplementingthistechnology. District Heating in the United States DistrictheatingintheUnitedStatesismainlybasedontheuse ofsteam,suchastheConEdisonSteamdistrict heating systeminNewYorkCityandtheCitizensThermalEnergy Copyrght©2007byASME