As the world grapples with the pressing need to reduce carbon emissions and combat climate change, Carbon Capture, Utilization, and Storage (CCUS) has emerged as a crucial technology. CCUS offers a pathway to mitigate the effects of carbon dioxide (CO2) emissions by capturing the gas at its source, utilizing it in various industrial processes, or storing it deep underground. However, implementing CCUS on a large scale presents a myriad of challenges, particularly in the realm of materials science and engineering. Among these challenges, the development of reliable sealing solutions for CO2 handling equipment, such as valves, is paramount.
By Patrick Stephen, Product Manager, High Performance Elastomers, and Andrew Douglas, Materials Engineering Group Manager, James Walker
Companies with experience and knowledge in the oil and gas sector now provide materials and expertise for CO2 sealing applications and facing off against emissions. This article explores the challenges faced in CCUS, particularly related to valves, and highlights James Walker’s contributions to overcoming these obstacles.
The Growing Importance of CCUS
Carbon dioxide is ubiquitous in our daily lives, from the air we exhale to the fizz in our carbonated drinks. However, its accumulation in the atmosphere is a significant concern due to its central role in climate change. CCUS technologies aim to address this issue by capturing CO2 from industrial processes or directly from the air and utilizing it in various ways, or securely storing it to prevent its release into the atmosphere.
The deployment of CCUS technologies is being driven by increasingly stringent climate goals and the need to decarbonize industries such as power generation, cement production, and chemical manufacturing. However, the scale and complexity of these operations introduce new challenges, particularly in the handling, transport, and storage of CO2.
Challenges in CO2 Handling and Storage
One of the most critical aspects of CCUS is ensuring the safe and efficient handling of CO2, especially when it transitions between its different phases — gaseous, liquid, and supercritical. At relatively low temperatures and pressures (around 31°C and 74 bar [1070 PSI]), CO2 enters a supercritical phase where it exhibits the properties of both a gas and a liquid. This phase change can have significant implications for the materials used in CCUS equipment, particularly seals.
Sealing Challenges in Valves for CO2 Applications
Valves play a crucial role in controlling the flow of CO2 in CCUS systems, making their reliability and performance vital to the overall success of the technology. However, sealing CO2, especially in its supercritical state, presents several unique challenges:
Rapid Gas Decompression (RGD): RGD is a well-known phenomenon in the oil and gas industry, where the rapid depressurization of a gas-saturated elastomer can cause catastrophic seal failure. In CCUS applications, the transition of supercritical CO2 (scCO2) back to a gaseous state, and the resulting volume increase, can trigger severe RGD damage, making it a significant concern for valve seals.
Swell and permeation: scCO2 can cause significant swelling in certain elastomeric materials used in seals. The degree of swelling can vary even within elastomers of the same type, making material selection critical.
Leaching: the solvent properties of scCO2 can result in the leaching of fillers and other components from elastomer compounds. This process can lead to a reduction in the seal’s mass and volume, adversely affecting its sealing performance and longevity.
Glass transition temperature (Tg) suppression: interestingly, scCO2 can lower the glass transition temperature of some elastomers, potentially improving their low temperature sealing performance by a few degrees. This effect is inconsistent across all elastomers and must be carefully considered during material selection.
Despite these challenges and the known effects of CO2 on elastomer seals, the industry lacks standardized testing protocols for validating these seals in CO2 applications. Consequently, we must rely on existing validation techniques to determine the suitability of a compound. ISO 23936-2 (NORSOK M-710) serves as an excellent benchmark, allowing the substitution of standard gas mixtures with CO2 for bespoke RGD testing. By adhering to the principles of this standard, it is possible to broaden the scope of testing to include variables beyond just the gas itself, such as test temperature and seal cross-section, to challenge materials rigorously.
Expertise in CO2 Sealing
After decades of work in the oil and gas sector, companies like James Walker have developed an understanding of the challenges associated with high pressure sealing. As early as twenty years ago, CO2 reinjection wells used in enhanced oil recovery (EOR) required players in the field to hone high-pressure seal techniques.
Elastomer products are being extensively tested in high-CO2 environments, including supercritical conditions. These materials have demonstrated particular resistance to CO2 – induced RGD and leaching, with resistance to high levels of swell seen in other similar compounds, making them ideal candidates for CCUS applications.
Certain elastomer products like James Walker’s Vermilion® Four have been subjected to rigorous RGD testing in environments with high CO2 levels and elevated temperatures, with outstanding results, leading to its selection for deployment in a significant North American CO2 pipeline project. Similarly, Vermilion Two has been accepted by operators of a major European carbon capture project after undergoing evaluation in stringent conditions at a third-party laboratory. By testing at elevated temperatures, and successfully achieving a perfect result of 0000 when evaluated using the ISO 23936-2 acceptance criteria, the materials provide the confidence that they will work in safety critical applications.
Conclusion
As the world moves towards a low-carbon future, CCUS technologies will play an increasingly important role in reducing greenhouse gas emissions. However, the successful deployment of CCUS depends on overcoming a range of technical challenges, particularly in the handling and storage of CO2.
Valves, as critical components in CCUS systems, require sealing solutions that can withstand the unique demands of CO2, especially in its supercritical state. These demands are significant, and careful consideration is needed in material and product selection to mitigate risks and increase safety margins.
Companies like James Walker, who has extensive experience in the oil and gas sector, now provide a solid foundation for addressing the challenges of CCUS. Their expertise in high-pressure and high temperature sealing applications, combined with their knowledge of CO2’s unique properties, make them well-fitted to tackle the challenges of CCUS. As the industry evolves and the technologies employed to tackle these challenges continue to develop, the demand for high-performance sealing solutions will increase, underlining the significance of expertise in this area.
In summary, while CCUS poses considerable challenges, particularly in CO2 sealing, the specialized knowledge and experience of companies working in this field provide viable solutions. Continued research and development in this area are essential for the successful implementation of CCUS technologies, contributing to a more sustainable future.