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.


The effect of CO2 concentration in the atmosphere on temperature has been known for a long time1. Although an increase in CO2 concentration has been observed since the 1960s2, a clear change in trend of global temperature increase can be observed from around the 1990s3. CCS (Carbon Capture and Storage) is a mature technology available to reduce emissions from large scale fossil-based energy and industry sources. Sufficient geological storage is available for these sources. Mitigation of CO2 emissions via CCS has been identified as crucial to limit global warming.3 In recent years a significant increase in CCS projects have been proposed and initiated4. A number of these projects aim to capture CO2 from multiple industrial sources (emitters) to reduce the carbon footprint for these companies.

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