12th International Symposium on District Heating and Cooling

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The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estonia15 °C, an <strong>International</strong> Standard Atmosphere (ISA)reference temperature [9], and calculated in thefollowing manner:Where(1)is the specific primary energy content inkJ/kg, is the enthalpy of the fluid and isthe saturated liquid enthalpy of the fluid at standardreference temperature of 15 °C.LIFE CYCLE ASSESSMENTThe Directive 2002/91/EC defines the concept ofprimary energy as energy that has not undergone anyenergy conversion process [1]. The primary energyfactor must thus represent all the primary energyconsumed in order to provide one unit of heat or powerto the consumer. Primary energy consumption ofenergy chains is not only based on the consumption offuel (or other energy source) in the power or heatgeneration process, but also all the primary energyneeded for the construction, operation and possiblydemolition of the production facilities. Also, someprimary energy is needed for the distribution of theproduct. To calculate such accumulated primaryenergy, the method of life cycle assessment is wellsuited. LCA is a method that has been developingsince the earliest performance of such a study in 1969and standards on the methodology where issued in thelate 1990s [10].LCA has been considered a good tool to achieve aholistic approach on evaluating the environmentalimpact of products. Today, it is widely used toinvestigate all kinds of production systems and hasgiven valuable insight on the total impact of productsand systems on the environment by not only focusingon the operational aspect [11]. Many interesting resultshave been achieved by using this methodology andthose results form a basis for evaluating and comparingdifferent solutions for production of various products,such as vehicles for transport, soft drink containers andpower conversion technologies. On the other hand,LCA in the process industry has had much lessattention than for manufacturing products, andresearch is needed before complete methods forprocesses are readily available [11]. The application ofLCA on geothermal energy utilization can be valuablefor LCA developers working on further improvementsand adjustments on the LCA methodology for theprocess industry.Using LCA to calculate the total primary energyconsumption and CO 2 emission for heat and powerproduction based on geothermal energy will helpidentify how much effect the construction, collection ofgeothermal fluid and even the demolition phase of thepower plant and the distribution system have on thetotal primary energy consumption. It can identify theimpact of the drilling of wells, manufacturing of powerplant components and piping, construction of buildingsand roads associated with the power plant, operation ofthe power plant itself and the primary energy extractedfrom the geothermal reservoir and even the impacts ofconstructing and operating the distribution facilities.The different phases of performing LCA will bedescribed in the following sections. The main phases ofLCA include:Defining the goal and scope of the studyPerforming inventory analysisPerforming impact assessmentGoal and Scope of the StudyThe main goal of this LCA study is to analyze the twoenergy performance indicators presenting the primaryenergy efficiency and the CO 2 emissions for both theelectricity and heat production at Hellisheidi powerplant. The LCA calculations and impact assessmentwhere done by using the LCA software SimaPro 7 [12]and using different databases such as the Ecoinventdatabase [13] for the inventory information on variousraw materials and processes used in the geothermalpower plant.There are numerous geothermal power plantsworldwide using similar technology as the Hellisheidipower plant to produce electricity (double flash powerplants produced 23% of the electrical power fromgeothermal resources in 2007 [14]), so the results forthe energy performance indicators for the powerproduction at Hellisheidi could be used to representthese power plants. Other types of geothermal energyconversion systems, such as single flash and binarysystems, should be treated individually whencalculating energy performance indicators for theelectricity production.Geothermal combined heat and power plants are notcommon worldwide, but regarding Europe they can befound in Iceland as well as Austria and Germany. Byproducing heat as well as electricity in geothermalapplications, the utilization of the heat taken from thegeothermal reservoir in the form of geothermal fluid ismaximized. The heat produced has a variety of usefulapplications, such as for district heating, agriculture,fisheries, swimming pools, snow melting and heatingup greenhouses [3]. The calculations of the primaryenergy factor of the heat production at Hellisheidigeothermal CHP plant will emphasize this increase inthermal efficiency of the power plant.187
The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaThe scope of this LCA study includes making thefollowing choices [11]:Functional unitSystem boundariesChoice of impact categoriesMethod for impact assessmentPrinciples for allocationData quality requirements1 kWh electricity1 kWh heatElectricity,geothermal, atHellisheidi CHPplantGeothermalfluid, fromelectricityproductionHeat, fromcondenserHeat,geothermal, atHellisheidi CHPplantGeothermalpower plant unitGeothermalfluid, at powerplantCollectionpipelinesGeothermalheat productionunitPower plantequipmentPower plantstructuresGeothermalfluid, in groundDrilling ofgeothermalwellsHeating stationStructureHeating stationequipmentFigure 2: Flow model for the life cycle assessment of the Hellisheidi CHP plantFunctional UnitThe primary energy and CO 2 factors are defined asprimary energy usage and CO 2 emission per MWh andthus, the functional unit of the study is chosen to beMWh of electricity or heat produced in the Hellisheidigeothermal CHP plant. The functional unit is thereference flow to which all other modelled flows of thesystem are related.System BoundariesThe processes included in this LCA study are mainlythe operation and construction of the power plant. Thedemolition or end-of-life phase is disregarded due toinsufficient information at this time. Also, the energyand material flows due to maintenance in theoperational phase of the power plant are disregardedbut both the demolition and the maintenance will beincluded in further studies. The time horizon in thisstudy is chosen to be 30 years, which is the technicallifetime of the power plant capital goods.A flow model of the CHP plant as modelled in the LCAstudy is shown in Figure 2. The two outputs of theproduction system are 1 MWh of electricity and 1 MWhof heat. The main material and energy inputs into theenergy conversion system are the geothermal power188plant unit, the geothermal heat production unit and thegeothermal fluid. The geothermal power plant isconstructed from the power plant structures andequipment while the fluid is transported in collectionpipelines from geothermal wells that need to be drilledfor the production. The heat production unit consists ofthe heating station structure and equipment. Theenergy input into the heating process is waste heatfrom the power production process in form of heattaken from the steam in the condenser for preheatingof district heating water, and the waste geothermal fluidfrom steam separators used for final heating of thedistrict heating water. Inventory data on all thesedifferent components in the flow model was collectedand used for the LCA study of the Hellisheidi CHPplant.Impact Categories and Methods for ImpactAssessmentTo calculate the two energy performance indicators,the two main impact categories to be used are theprimary energy demand of the production process inMWh and Global Warming Potential (GWP) given inCO 2 equivalents.
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Stockholm district heating system a
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12th International Symposium on District Heating and Cooling

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