Carbon removal efficiency and energy requirement of engineered carbon removal technologies

Abstract

To ensure carbon negativity, processes that achieve carbon dioxide removal (CDR) from the atmosphere must consider lifecycle emissions and energy requirements across the entire system. We conduct a harmonized lifecycle greenhouse gas assessment to compare the carbon removal efficiency and total energy required for twelve engineered carbon removal technologies. The goal of this comparison is to enable the assessment of diverse engineered carbon removal approaches on a consistent basis. Biomass-based CDR approaches generally maintain higher carbon removal efficiency than direct air capture (DAC) and, to a lesser extent, enhanced rock weathering (ERW) due to the high concentration of carbon within the biomass and the relatively low energy requirements for processing the biomass for removal. Nevertheless, there is high variance in CDR approaches, as some biomass conversion processes (e.g., pyrolysis for biochar or gasification for fuels) exhibit high, yet variable, carbon losses, while DAC and ERW can utilize low-carbon energy inputs for more efficient removal. Regarding energy use, ERW and biomass-based approaches generally require less energy than DAC today, but biomass approaches again exhibit more variation. Displacement of products, when included, increases the total climate benefits of biomass used for bioenergy with carbon capture and storage (BECCS) and biochar. These two measures are intuitive metrics to guide allocation of scarce resources amongst potentially competing uses of biomass and low-carbon energy.