UC Berkeley

AbstractLeveraging the Bioeconomy for Carbon Drawdown By John Paul Dees Doctor of Philosophy in Energy and Resources University of California, Berkeley Professors Daniel M. Kammen and David Anthoff, Co-chairs

The role of the bioeconomy in climate change mitigation has been, at times, both contested or framed in a limited manner to include only bioenergy with carbon capture and sequestration (BECCS) technologies. This dissertation contributes to a more expansive framework wherein the bioeconomy services distinct and dynamic near, medium, and long-term decarbonization needs. Products of the bioeconomy can serve as both fossil fuel replacement in “hard-to-abate” sectors as well as providing a carbon storage medium for biomass carbon removal and storage (BiCRS), an emerging framework with a more expansive opportunity set for carbon removal than BECCS alone. This dissertation builds on existing literature, starting with a review of the BiCRS literature and a supplementary novel analysis of the climate impact potential of BiCRS technologies in the near-term. The subsequent chapters offer cost and climate impact assessments for biomass utilization in the transportation sector. The bioeconomy already services substantial decarbonization needs in light duty transportation in the form of biofuels derived from starch, sugars, and oil crops. Chapter 3 explores the potential to further decarbonize ethanol production by capturing fossil boiler emissions via the integration of an oxyfuel boiler. Chapter 4 explores the potential of drop-in biofuels in the “hard to abate” aviation sector through a comparative analysis of the cost, climate impact, and scalability of sustainable aviation fuel technologies and feedstocks. The overarching finding of this dissertation is that there are meaningful, cost-effective opportunities to deploy bio-based products for decarbonization and carbon removal, particularly in economic sectors where there are few if any other near-term options.

Stringent climate change mitigation scenarios rely on large-scale drawdown of carbon dioxide from the atmosphere. Amongst drawdown technologies, BECCS has received considerable attention in the climate mitigation literature. Recently, attention has shifted further from a relatively narrow focus on BECCS to a broader focus on BiCRS. The concept of BiCRS has the potential to enable a future where the climate mitigation value of biomass resources is more valuable than the energy value, due to the potential to remove and sequester large quantities of atmospheric CO2. There are numerous opportunities to incorporate carbon removal and management within the bioeconomy, but the majority of immediate carbon removal potential exists in four bioproducts: bioenergy, bioplastics, biochar, and wood products. Chapter 2 analyzes the life cycle greenhouse gas emissions and disposition of sequestered carbon over 10,000 years for four bioproducts representative of each broader category: an advanced BECCS pathway, biopolyethylene, oriented strand board, and biochar soil amendment. The analysis shows that the BECCS pathway has the greatest magnitude and durability of CO2 storage over all time horizons. However, non-BECCS pathways achieve 34-64% of the drawdown magnitude relative to BECCS and retain 55-67% of their initial drawdown over 100 years (central estimate). This work identifies three engineering strategies for enhancing carbon drawdown: reducing biomass supply chain emissions, maximizing carbon stored in long-lived products, and extending the term of carbon storage. In the larger context of this work, the analysis demonstrates that the bioeconomy can service potentially higher-value economic needs than the energy sector alone, while removing and storing atmospheric carbon over climate-relevant timeframes.

Within the energy sector, the bioeconomy still has a near-term role to play in transport decarbonization. Decarbonization of transportation fuels represents one of the most vexing challenges for climate change mitigation. Biofuels derived from corn starch have offered modest life cycle greenhouse gas (GHG) emissions reductions over fossil fuels. This work shows that capture and storage of CO2 emissions from corn ethanol fermentation achieves ~58% reduction in the GHG intensity (CI) of ethanol at a levelized cost of 52 $/tCO2e abated. The integration of an oxyfuel boiler enables further CO2 capture at modest cost. This system yields a 75% reduction in CI to 15 gCO2e/MJ at a minimum ethanol selling price (MESP) of $2.24, a $0.31/gallon increase relative to the baseline no intervention case. The levelized cost of carbon abatement is 84 $/tCO2e. Sensitivity analysis reveals that carbon neutral or even carbon negative ethanol can be achieved when oxyfuel carbon capture is stacked with low-CI alternatives to grid power and fossil natural gas. Conservatively, fermentation and oxyfuel CCS can reduce the CI of conventional ethanol by a net 44-50 gCO2/MJ. Full implementation of interventions explored in the sensitivity analysis would reduce CI by net 79-85 gCO2/MJ. Integrated oxyfuel and fermentation CCS is shown to be cost effective under existing U.S. policy, offering near-term abatement opportunities.

The role of biofuels is likely to diminish in ground transport as electrification provides more cost and climate effective alternatives. However, commercial aviation is not amenable to electrification at scale in the near future, thus there is an imminent role for the bioeconomy. Aviation is termed a “hard to abate” sector as there are few viable decarbonization options for air transport at present due to safety considerations, infrastructure, and technical hurdles. Drop-in sustainable aviation fuels (SAF) produced from biomass or CO2 are widely-viewed as the most viable near-term alternatives to fossil jet fuel. There are many technical pathways to produce SAF, and their costs and impact on climate and food systems differ significantly. The work presented here sets sustainability and cost criteria to produce 10 billion gallons of SAF in the United States by 2030 and assesses the viability of SAF production technologies and feedstocks against those criteria. The analysis indicates the greatest opportunity in the production of Fischer-Tropsch and Alcohol-to-Jet fuels. These production pathways are amenable to waste and residue feedstocks, minimizing the impact on food systems and land use emissions. Moreover, they are compatible with relatively low-cost carbon capture and sequestration technologies which can yield carbon negative fuels. Given existing U.S. policies, the technoeconomic assessment of these pathways indicates that in many contexts, subsidized costs may be competitive with commercial Jet-A.

The scope of the work in this dissertation highlights the significant and varied roles that the bioeconomy can play in climate mitigation while recognizing that sustainable biomass is a limited resource that should be targeted at its highest value uses.