The case for estimating carbon return on investment (CROI) for CCUS platforms

Abstract

Development of CO2 capture, utilization, and storage (CCUS) platforms has been deemed crucial for achievement of the Paris Agreement goals. Life-cycle assessment (LCA) is an important tool for assessing the efficacy of these technologies in achieving true net-carbon reduction. Critical review of previously published LCA-based evaluations of CCUS technologies reveals that there is an urgent need for more transparent accounting of carbon removal efficiency. Updated methods should incorporate better focus on the CO2 uptake as the primary objective and better differentiate apportionment between “avoided emissions” and true net sequestration. We posit that widespread, uniform application of a standardized ratio metric, carbon return on investment (CROI), will improve the usefulness of LCA to articulate true CO2 sequestration by candidate CCUS platforms. We present two case studies to illustrate the value of this metric for diverse CCS and CCU applications. We also provide several recommendations to make future CROI results as unambiguous as possible and boost their usefulness. These recommendations pertain to conventional LCA concepts, including: choice of functional unit (or declared unit) and system boundaries, application of system expansion, and proper mathematical formulation of the proposed metric. Future work should aim at carrying forward our work on proposed minimum CROI and incorporating the time-value of CO2 fluxes.