June 5 – 10, 2022
Thermal waste treatment of municipal solid waste (MSW), e.g., Waste-to-Energy (WtE), plays a crucial role within future waste management schemes. The ability it creates to recover both energy contained in nonrecyclable waste, as well as valuable materials from bottom ash, proves its role as an essential and compatible technology within the circular economy. WtE technology can be strategically positioned in sustainable industrial symbiosis, wherein the recovered energy from the WtE plant, e.g., high-pressure steam, is delivered to neighbouring industries via local networks. This study considers such a case: Indaver/Sleco’s WtE plant in Doel, Belgium, is connected to both a steam turbine and the surrounding chemical industry via a high-pressure steam network (ECLUSE). A Life Cycle Assessment (LCA) was conducted to critically evaluate the total environmental impact of the state-of-the-art WtE plant with respect to recovered energy utilisation and the addition of Carbon Capture and Storage (CCS). Four energy output scenarios were modelled on Umberto LCA software using primary data of mass and energy flows surrounding the six incinerators at the considered WtE plant, and predefined processes from the Ecoinvent 3.6 database. The four scenarios varied in the way that the recovered energy from the WtE plant was utilised; the corresponding LCA results were compared to identify the influence of energy substitution on the environmental performance of the WtE plant. Furthermore, one scenario modelled the addition of a hypothetical CCS unit coupled to the WtE plant. 2018 International Life Cycle Data system (ILCD) methodology was used to calculate the environmental impacts for the four scenarios. The normalised LCA results – for the ILCD recommendation level I and II impact categories – indicate that if all the recovered energy is utilized as high-pressure steam, the WtE plant can avoid the highest environmental impacts, i.e. approximately 21200, 36800, 6700, 15800, 37000, and 6900 average European citizens equivalents (AECE) in the impact categories ‘climate change’, ‘freshwater and terrestrial acidification’, ‘freshwater eutrophication, ‘photochemical ozone creation’, ‘respiratory effects, inorganics’, and ‘terrestrial eutrophication’, respectively. By capturing CO2 from the flue gas using a conventional amine-based carbon capture technique, the WtE plant can avoid a further impact in the impact category ‘climate change’. However, in all other impact categories, the scenario with CCS resulted in less avoided environmental impact compared to the scenario that utilizes the recovered energy as high-pressure steam, due to the high energy demand and additional auxiliary input and outputs affiliated with operating the CCS unit itself. A comparative analysis was conducted to investigate the influence of scenario uncertainty, introduced by the normative choice of substituted energy production processes on the overall environmental impact of the WtE system. For the first model, the Region Specific Model, the processes chosen for the substituted energy production of electricity and steam were based on regionalized impact data, which is commonly used in LCA to reduce uncertainty introduced by spatial variability. In the second model, the Region and Fuel Specific Model, the processes chosen were based on regionalized data as well as a specific fuel type, i.e. natural gas. The results of the comparative analysis of the two models showed that 19 out of 24 of the normalized LCA results varied by more than 50 %, thus quantifying the influence of scenario uncertainty introduced by the normative choice of substituted processes in LCA modeling. The scenarios that produced electricity showed improved normalized environmental impact values in the Region and Fuel Specific Model compared to the Region Specific Model. For instance, the environmental impact in the impact category ‘climate change’ was approximately 42,000 AECE for the scenario that only produced electricity in the Region Specific Model, and was reduced to approximately 14,000 AECE (reduction of 67%) in the Region and Fuel Specific Model. The results of this comparative analysis demonstrate that decision-makers would not draw the same conclusions when analysing the results of the two models, confirming that scenario uncertainty, introduced by the normative choice of assumed substituted processes, has a significant effect on the LCA results. It was suggested that finding consensus among stakeholders on data and assumption choices will lead to more representative results. Conclusively, this study demonstrates that Indaver/Sleco’s WtE plant in Doel can achieve the highest avoided environmental impacts by utilising the recovered energy as high-pressure steam and delivering it to the local chemical industry via the ECLUSE high-pressure steam network. It thus proves the environmental benefit WtE technology can realise, by substituting conventional energy production processes that are reliant on fossil primary resources, whilst performing its primary function that is reducing the volume and mass of non-recyclable waste and recovering useful materials from it. Furthermore, this study shows that if in the future electricity production becomes less carbon-intensive, WtE can still realises significant environmental benefits by exporting energy as heat.
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Lizzie Boakes, "The influence of energy output and substitution on the environmental impact of waste‐to‐energy operations" in "WasteLCA_3: Life Cycle Sustainability Assessment For Waste Management And Resource Optimization", Umberto Arena, University of Campania “Luigi Vanvitelli”, Italy; Thomas Astrup, University of Denmark, Denmark Eds, ECI Symposium Series, (2022). https://dc.engconfintl.org/lca_waste_3/50