12th International Symposium on District Heating and Cooling

(see Environmental evaluation) and, hence, there is anegative bar of 8 Mtonne for biomass. To sum up, thenet GHG reduction in the reference case is 30 or 108Mtonne CO 2 equivalents depending on assumptions forthe marginal electricity.The combine case of System 3 has lower electricityproduction than in the reference case (see Descriptionof the cases). Consequently, the GHG reduction fromthe electricity production is also lower, which is seen aslower dark and light blue bars for the combine case;middle stacked bar in Fig. 2. Moreover, the negativebar for biomass is larger for the combine since morebiomass is used in this case. In the energy combine,however, bioenergy products such as biofuel (ethanolin this system), biogas and pellets are produced. Asalready explained, these energy products are assumedto replace fossil fuels and the resulting GHG reductionfrom the combine is significant: 188 or 217 Mtonne CO 2eq. with carbon lean (E2) and carbon intense (E1)electricity production, respectively.GHG reduction (Mtonne CO 2 eq./yr)3002001000-100-200Net reduction (E2/E1):30/108 188/217 158/109Reference Combine DifferenceElectricity, E1-E2*Electricity, E2PelletsBiogasEthanolBiomass* additonal emissionreduction/change ifelectricity is relatedto high CO 2 emissionsFig. 2. GHG reduction in System 3 for the reference case,combine case and the net difference for converting to thecombine.The dark blue bars are related to marginal electricityassociated to low GHG emission (E2). The additionalemission reduction/change if electricity is related tohigh GHG emissions (E1–E2) is indicated by the lightblue bars. The total emission/change for E2 is given bythe sum of light blue and dark blue bar.The implication in terms of GHG‘s of integratingbioenergy production in System 3 can be visualised bymoving from the left bar in Figure 2 to the middle bar.Consequently, the difference of the two bars shows theGHG implication of converting to an energy combine inSystem 3, which is presented in the right hand bar inthe figure. The change from the reference to thecombine case gives rise to GHG reduction from the fuelproducts (green bars) However, the electricityproduction decreases, implying decreased reduction(emission increase) and, hence, negative bars forelectricity. As can be seen in the figure, the net GHGThe <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estonia148reduction from introducing an energy combine inSystem 3 is 158 or 109 Mtonne/year depending on theassumption for marginal electricity (E2 and E1,respectively).The equivalents to the right hand bar in Figure 2 for allfour systems are shown in Figure 3. As can be seen,the reductions of GHG‘s are significant in systems 2-4,especially if the electricity is associated with lowemissions (E2, dark blue bar only). In System 1, theenvironmental benefit is negative, even if the marginalelectricity is CO 2 lean.Significant environmental benefits, as displayed forsystems 2-4, are expected since the combines in thesesystems use more biomass, which eventually replacesfossil fuel in the system approach applied (in system 1less biomass is used which explains the negativeresults for this system). However, if biomass isassumed to be a limited resource from sustainabilitypoint of view, the use of biomass should also beevaluated from an efficiency point of view. As explainedin the Environmental evaluation, one measure ofresource efficiency is the GHG reduction potential perused quantity of biomass. This key figure is presentedin Figure 4 for both the reference case and thecombine case for the four district heating systemsevaluated.GHG reduction (Mtonne)400350300250200150100500-50-100-150Net reduction (E2/E1):-2/-69 124/119 158/109 321/309System 1 System 2 System 3 System 4Others*BiofuelElec., E1-E2Elec., E2Biomass* biogasand pelletsFig. 3. Environmental benefit from introduction of energycombines.As seen in Figure 4, the energy combines are lessresource efficient than the reference cases (generally abiomass fired CHP plant) if the marginal electricity isassociated with high CO 2 emissions (E1, dark + lightblue bar). However, if the marginal electricity isassociated with low CO 2 emissions (E2, dark blue baronly), the combines are more resource efficient thanthe reference cases. As also can be seen, the resourceefficiencies do not differ dramatically betweensystems 2–4. System 1, however, shows lowerresource efficiency, which can be explained by the factthat a major part of the produced pyrolysis oil isconsumed internally in the system instead of replacingfossil fuel off site.