CO₂ Transport and Injection, Effect of Impurities, Understanding of Reactions and Consequences

Carbon Capture and Storage (CCS) involves capturing, treating, transporting and storage of CO₂ to ensure long-term isolation from the atmosphere. In recent years there has been a significant increase in CCS project proposed and initiated. A number of these proposed projects aim to capture CO₂ from multiple industrial emitters (sources) to reduce the carbon footprint for these companies.

Depending on the CO₂ composition and operating conditions, separate liquid phases may be formed. It has been identified that these phases can comprise of water or reaction products including strong acids and elemental sulphur. Exposure to (impure) CO₂ at specific operating conditions can also negatively impact specific material properties causing a change in toughness and cracking resistance. To ensure long term integrity of the facilities, a safe project CO₂ specification needs to be identified. Tight control of CO₂ stream composition and operating conditions together with the selection of suitable materials are essential to ensure the integrity for all operating scenarios including upsets.

This paper focuses on identification of impurity limits for a CCS project, which is captured in a project CO₂ specification. Special attention given to one specific group of impurities that can react with each other and form a strong acids and elemental sulphur, that can cause a separate phase that can drop out of the CO₂ stream. Sound understanding of the mechanisms behind these chemical reactions, thermodynamics, the role phase behaviour plays and potential consequences are needed to be able to identify or adjust (relax or tighten) impurity limits for a project CO₂ specification. This work aims to improve understanding provide guidance and to reveal knowledge gaps that require addressing in order to identify a safe CO₂ specification for a CCS project.