Biofuels like biodiesel and biomethane are considered a valid alternative to reduce fossil fuels consumption while also tackling the climate change issue. Today in Europe most of biodiesel and biomethane are produced respectively from rapeseed and maize, easily grown energy crops. However, the research is moving towards biofuels from non-crop feedstocks or cultures from marginal soils. With this in mind, two perennial plants, needing less care and management during cultivation, are included in this analysis: jatropha curcas for biodiesel and miscanthus for biomethane. This study focuses only on the biofuel carbon footprint, calculated from well-to-wheel (WTW), comparing it to that of the substituted fossil fuel. Considering the biofuel for use in a heavy-duty truck, biodiesel should displace diesel, whereas compressed or liquefied biomethane should replace compressed or liquefied natural gas. Life cycle inventories are built with data from recent European-specific literature, to reproduce what actually happens in European production plants. Current European mixes for the main energy resources, such as diesel, natural gas, gasoline and electricity, are implemented or updated in Greet. Since both biofuels studied present co-products along their production chain, it is necessary to adopt an allocation method. Three different allocation techniques, no allocation, energy- and mass-based allocation, are used to achieve a more complete assessment. For simplicity, WTW results are mean values among the different allocation scenarios for each biofuel, presented in kgCO2,eq/km. In this study, rapeseed biodiesel yields mean global warming potential (GWP) of 0.16 kgCO2,eq/km, with 81% reduction compared to diesel; jatropha biodiesel achieves GWP of 0.28 kgCO2,eq/km, with 67% reduction from diesel, thus being outperformed by rapeseed. This is because the latter is cultivated in Southeast Asia or Central America, yielding massive greenhouse gas (GHG) emissions during oceanic transport. A future development of this work could be considering jatropha farming in Southern Europe or Africa, to reduce the impact of transportation. Maize biomethane achieves GWP of 0.35 kgCO2,eq/km, with 64% reduction compared to natural gas, whereas miscanthus has mean GWP of 0.29 kgCO2,eq/km, with 70% reduction from natural gas. Percentage saving is lower than biodiesel since it is calculated in regard to natural gas, already less emitting than diesel; if biomethanes were to be confronted with diesel, savings would rise. Additionally, five ready-to-go biofuels from Greet are included in a final comparison of WTW results. Most of them produce biodiesel and biomethane starting from various wastes, namely tallow, animal waste, municipal solid waste and wastewater sludge. This upcycling prevents the common waste management practices, avoiding associated emissions which are credited to the biofuel production system. As a result, waste biomethanes mean GWP is greatly reduced, amounting to -0.62 kgCO2,eq/km, with 166% reduction from natural gas. Differently, tallow biodiesel doesn’t have an avoided counterfactual scenario, yielding a positive, though limited, GWP. In light of the obtained results, it would be interesting to perform complete LCAs of biofuels from wastes.
Biocarburanti come il biodiesel e il biometano sono considerati una valida alternativa per ridurre il consumo di combustibili fossili, affrontando al contempo la questione del cambiamento climatico. Oggi in Europa la maggior parte del biodiesel e del biometano sono prodotti rispettivamente da colza e mais, coltivazioni a scopo energetico. Tuttavia, la ricerca si sta muovendo verso biocarburanti provenienti da materie prime non agricole che possono essere cresciute su terreni marginali. In quest'ottica, due piante perenni, che necessitano di meno cura e gestione durante la coltivazione, sono incluse in questa analisi: jatropha curcas per il biodiesel e miscanto per il biometano. Questo studio si concentra solo sull'impronta di carbonio dei biocarburanti, calcolata well-to-wheel (WTW), confrontandola con quella del combustibile fossile sostituito. Con l'intento di usare il biocarburante in un autocarro pesante, il biodiesel dovrebbe sostituire il gasolio, mentre il biometano compresso o liquefatto il gas naturale compresso o liquefatto. Gli inventari del ciclo di vita sono costruiti con i dati della recente letteratura specifica europea, per riprodurre ciò che accade effettivamente negli impianti di produzione europei. Gli attuali mix europei per le principali risorse energetiche, come diesel, gas naturale, benzina ed elettricità, sono implementati o aggiornati in Greet. Poiché entrambi i biocarburanti studiati presentano co-prodotti lungo la loro catena di produzione, è necessario adottare un metodo di allocazione. Tre diverse tecniche di allocazione, nessuna allocazione, allocazione basata sull'energia e sulla massa, vengono utilizzate per ottenere una valutazione più completa. Per semplicità, i risultati WTW sono valori medi tra i diversi scenari di allocazione per ogni biocarburante, presentati in kgCO2,eq/km. In questo studio, il biodiesel da colza raggiunge un potenziale di riscaldamento globale (GWP) medio di 0.16 kgCO2,eq/km, con una riduzione dell'81% rispetto al diesel; biodiesel da jatropha raggiunge un GWP medio di 0.28 kgCO2,eq/km, con una riduzione del 67% dal diesel, una prestazione peggiore della colza. Questo perché quest'ultimo è coltivato nel sud-est asiatico o in America centrale, producendo massicce emissioni di gas serra (GHG) durante il trasporto oceanico. Uno sviluppo futuro di questo lavoro potrebbe essere la valutazione della coltivazione di jatropha nell'Europa meridionale o in Africa, per ridurre l'impatto dei trasporti. Il biometano da mais raggiunge un GWP di 0.35 kgCO2,eq/km, con una riduzione del 64% rispetto al gas naturale, mentre il miscanto ha un GWP media di 0.29 kgCO2,eq/km, con una riduzione del 70% dal gas naturale. Il risparmio percentuale è inferiore al biodiesel in quanto è calcolato rispetto al gas naturale, che emette meno del diesel; se i biometani venissero confrontati con il diesel, i risparmi salirebbero. Inoltre, cinque biocarburanti pronti all'uso in Greet sono inclusi in un confronto finale dei risultati WTW. La maggior parte di essi produce biodiesel e biometano a partire da vari rifiuti, vale a dire sego, rifiuti animali, rifiuti solidi urbani e fanghi di acque reflue. Questa valorizzazione evita le pratiche comuni di gestione dei rifiuti, evitando le emissioni associate, accreditate al sistema di produzione di biocarburanti. Di conseguenza, il GWP medio dei biometani da scarti è notevolmente ridotto, pari a -0.62 kgCO2,eq/km, con una riduzione del 166% dal gas naturale. Diversamente, il biodiesel di sego non ha uno scenario controfattuale evitato, producendo un GWP positivo, anche se limitato. Alla luce dei risultati ottenuti, sarebbe interessante eseguire LCA completi di biocarburanti provenienti dai rifiuti.
Life cycle carbon footprint of biodiesel and biomethane powering heavy-duty vehicles
GIUSSANI, SARA
2019/2020
Abstract
Biofuels like biodiesel and biomethane are considered a valid alternative to reduce fossil fuels consumption while also tackling the climate change issue. Today in Europe most of biodiesel and biomethane are produced respectively from rapeseed and maize, easily grown energy crops. However, the research is moving towards biofuels from non-crop feedstocks or cultures from marginal soils. With this in mind, two perennial plants, needing less care and management during cultivation, are included in this analysis: jatropha curcas for biodiesel and miscanthus for biomethane. This study focuses only on the biofuel carbon footprint, calculated from well-to-wheel (WTW), comparing it to that of the substituted fossil fuel. Considering the biofuel for use in a heavy-duty truck, biodiesel should displace diesel, whereas compressed or liquefied biomethane should replace compressed or liquefied natural gas. Life cycle inventories are built with data from recent European-specific literature, to reproduce what actually happens in European production plants. Current European mixes for the main energy resources, such as diesel, natural gas, gasoline and electricity, are implemented or updated in Greet. Since both biofuels studied present co-products along their production chain, it is necessary to adopt an allocation method. Three different allocation techniques, no allocation, energy- and mass-based allocation, are used to achieve a more complete assessment. For simplicity, WTW results are mean values among the different allocation scenarios for each biofuel, presented in kgCO2,eq/km. In this study, rapeseed biodiesel yields mean global warming potential (GWP) of 0.16 kgCO2,eq/km, with 81% reduction compared to diesel; jatropha biodiesel achieves GWP of 0.28 kgCO2,eq/km, with 67% reduction from diesel, thus being outperformed by rapeseed. This is because the latter is cultivated in Southeast Asia or Central America, yielding massive greenhouse gas (GHG) emissions during oceanic transport. A future development of this work could be considering jatropha farming in Southern Europe or Africa, to reduce the impact of transportation. Maize biomethane achieves GWP of 0.35 kgCO2,eq/km, with 64% reduction compared to natural gas, whereas miscanthus has mean GWP of 0.29 kgCO2,eq/km, with 70% reduction from natural gas. Percentage saving is lower than biodiesel since it is calculated in regard to natural gas, already less emitting than diesel; if biomethanes were to be confronted with diesel, savings would rise. Additionally, five ready-to-go biofuels from Greet are included in a final comparison of WTW results. Most of them produce biodiesel and biomethane starting from various wastes, namely tallow, animal waste, municipal solid waste and wastewater sludge. This upcycling prevents the common waste management practices, avoiding associated emissions which are credited to the biofuel production system. As a result, waste biomethanes mean GWP is greatly reduced, amounting to -0.62 kgCO2,eq/km, with 166% reduction from natural gas. Differently, tallow biodiesel doesn’t have an avoided counterfactual scenario, yielding a positive, though limited, GWP. In light of the obtained results, it would be interesting to perform complete LCAs of biofuels from wastes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/176310