Impurities in CO₂ streams for a multi-user CCS hub

Abstract

A hub-based carbon capture and storage (CCS) project aggregates multiple sources of carbon dioxide (CO₂) from different industries. This adds complexity because of the varying levels and types of impurities that could be present in the CO₂ stream. To maintain technical integrity, optimise operational efficiency and ensure safety, CCS proponents and emitters must understand the effects of impurities, which affect every stage of the CCS value chain. The impurities can cause impacts such as changing phase behaviour, triggering chemical reactions that form corrosive acids, cause liquid dropout, reduce injectivity in the storage formation or impact material failure mechanisms. CCS projects define a stream specification to control impurity levels in captured CO₂, ensuring safe transport, injection and storage whilst preventing material degradation. Meeting these stringent specifications for impurity levels can be very costly, and current technology limitations in online monitoring analysers make it challenging to assure low levels of impurities have been met. Given that CCS is evolving there is a gap in developing strategies to effectively manage the impact of mixed CO₂ streams. This paper aims to share current industry knowledge about the effects of different impurities and the primary considerations when specifying limits of impurities. CCS CO₂ specification is unique and should be tailored to the impurity profile, transport system, the storage and ambient conditions. Key topics include describing the technical challenges of specifying impurities in CCS streams, and considerations in defining the CO₂ specification limit for dense phase CO₂ and liquid CO₂.