12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaCO 2 Emission CoefficientThe CO 2 rating is done by calculating CO 2 emissioncoefficients (c CO2 ) that quantify the total amount of fossilfuel derived CO 2 , emitted to the atmosphere, per unitdelivered energy. As for the primary energy factor thesystem boundary comprises of power plants and DHN.Also the power bonus method is applied for calculatingthe DHN‘s specific CO 2 emissions. For the sake ofcompleteness it must be mentioned that CO 2 -equivalentemissions of other greenhouse gases can optionally beincluded. However this has not been implemented intothis study, due to a lack of data. Similarly to the PEF theCO 2 emission coefficients for the base case arecalculated as:cCO2, DHiEF , icCO2, F , iQDHAnd for the modified plant as:cCO2, DHiEF , i cCO2, F , i P c P cQCO2, El .CO2, El .DH. EPyro cCO2, PyroE F,i , E Pyro , P and Q DH represent heat in fuels, heat inpyrolysis slurry and co-generated electricity and DHrespectively. Accordingly, c CO2,F,i , c CO2,Pyro , c CO2,El. andc CO2,DH are the related CO 2 emission coefficients. Thecorresponding values are given in table 2.RESULTSIn table 3, three simulation cases are presented: thebase case (case 1), pyrolysis integration with the sameoperation hours (case 2) and the maximum pyrolysisslurry production (case 3) with prolonged operation.hours and a DH load as low as 30% (matching 18% ofthe total DH load). It can be seen from the table that forall cases the DH output is the same for the 100-50%operating points. This results, in the first two cases, inan identical total DH output of 70.85 GWh. Thiscorresponds with 75% of the total yearly DH load. Dueto steam extracted to the dryer, the enthalpy flowthrough the turbine in part load is decreased, whichresults in a lower electricity production in part load forthe cases 2 and 3. Already for the second casepyrolysis slurry with an energy content in the samerange as the DH load can be produced. Fuel input,which is defined as wood burned in the boiler and woodentering the dryer for subsequent pyrolysis, increaseswith falling load for load levels 60% and higher. In thosecases the boiler combustion power is 100%, but it isdecreased for lower load levels as explained above. Ifoperation hours are extended by supplying lower DHloads with the CHP plant (case 3), total pyrolysis slurryproduction can be increased by approximately 55%,electricity production by 7.8% compared to the basecase. Further DH production is increased byapproximately 14.7%, covering now 86% of the total DHdemand. This directly decreases the fossil fuelledbackup power as shown in table 4. The needed backupheat is almost cut in half. Together with the additionallyproduced electricity this substantially improves theprimary energy factor to 0.68 which certainly will have apositive influence on the PEF of the buildings connectedto the DHN. For case 2 the improvement is marginal.The CO 2 emission coefficient changes somewhatcontroversially by increasing in the 2 nd case. This isbecause the loss in electricity bonus cannot becompensated by the produced pyrolysis slurry, since theCO 2 emission coefficients differ widely. However forcase 3 specific CO 2 emissions become even negative.The negative value is very unlikely to reach and can beexplained with the not fully accounted fuel productionchain. Nevertheless, it is obvious that the DHN‘s CO 2emission factors can be considerably reduced with thepresented integration concept.173