(485e) Optimization of Biomass to Fuels with Carbon Capture: Economic and Environmental Analysis

Bioenergy with carbon capture and sequestration (BECCS) combines fuel production with permanent carbon dioxide (CO₂) removal, and features prominently in many pathways identified that limit global warming to 1.5°C. BECCS involves converting biomass to a wide range of fuels, including ethanol, gasoline, diesel, electricity, or hydrogen. Depending on the pathway selected, a different number of point sources of CO₂ streams with different relative flows, pressures, and CO₂ concentrations may be present at the biorefinery. For example, a biorefinery that uses fermentation to convert lignocellulosic biomass to ethanol emits CO₂ in three different sources: in off-gas from fermentation, in biogas from wastewater treatment, and in flue gas from solid residue combustion.

We develop and use a mixed-integer nonlinear programming (MINLP) model to determine the combination of conversion technology, fuel type, and amount of carbon capture that result in the lowest breakeven cost of fuel production. We solve thousands of optimization problems with varying parameter values to investigate the impact of CO₂ sequestration credit, biorefinery capacity, and energetic self-sufficiency on the economic and environmental performance of pioneer and n^th plant biorefineries producing liquid fuels and capturing carbon. We then compare traditional liquid fuels to electricity and hydrogen, and find that biomass to electricity or hydrogen is economically preferred when costs are normalized to forward motion in vehicles, and environmentally preferred because there is the potential to capture more carbon at the biorefinery because there is no carbon in the fuel product. Finally, we examine how the greenhouse gas mitigation from a biorefinery producing electricity or hydrogen would be affected by temporal changes in the production mix of electricity and hydrogen.