Supply chain optimization for Ocean Alkalinity Enhancement: A Norwegian case study

Negative Emissions Technologies (NETs) can contribute to capture atmospheric CO₂ and mitigate climate change. One promising NET is Ocean Alkalinity Enhancement (OAE), which is the dispersal of slaked lime into ocean water to induce chemical processes that enhance the oceans’ CO₂ uptake capability. As OAE implementations are just evolving, there are various open questions. In this study, we focus on the design of OAE supply chain networks and propose a first optimization model for the Ocean Alkalinity Enhancement Supply Chain Optimization Problem (OAE-SCOP). The model aims at achieving a specified net CO₂ uptake at minimum cost by deciding on the establishment of extraction sites, processing plants, and ports, as well as investments in processing capacities and carbon capture and storage (CCS) technologies in the plants, the transport modes to use, the ship fleets involved for ocean distribution and the material flows within the entire network. It accounts for emissions generated by the supply chain processes, and balances these against the induced CO₂ uptake in the ocean. We apply the model to artificial test instances and a realistic case study in Norway. The results indicate that economies of scale could significantly reduce costs in large-scale implementations. Compared to land-based NETs, OAE seems more costly when considering purely financial metrics, but it may show the advantage of leveraging existing logistics networks for limestone processing and comes at less additional land use.