Strategies for CO₂ Purification: Insights from GHGT-17 Panel Session 5

On 23rd October 2024, Panel Discussion 5 at the GHGT-17 conference, titled “Strategies for CO₂ Purification,” convened leading subject matter experts (SMEs) to address the intricate challenges involved in purifying CO₂ streams. This technical session was chaired by Owain Tucker, a CCS expert and Capability Manager at Shell, with panellists including Ray McKaskle, Principal Engineer at Trimeric Corporation, John Woods, Principal Consultant at Wood, and Richard Porter, Principal Research Fellow at University College London.

The discussion delved into the intricacies of CO₂ purification, exploring the technical hurdles, potential solutions, and gaps in current knowledge that must be addressed to advance carbon capture, utilisation, and storage (CCUS) efforts.

Panellists at the technical panel discussion 5 at GHGT-17, titled Strategies for CO₂ Purification. From right: Owain Tucker, Richard Porter, John Woods and Ray McKaskle

Owain Tucker kicked off by setting the scene with an engaging analogy, likening the purification of a CO₂ stream with multiple gaseous contaminants to managing a room full of kids. While a youngster alone might be manageable, having a rowdy crowd makes the situation increasingly chaotic, just as a CO₂ stream with various contaminants presents escalating technical and economic challenges. Owain highlighted the significance of these impurities, noting that corrosion rates have been observed to exceed 10-50 cm/year in some cases, depending on the types of contaminants and feedstock involved. This variability underscores the need for tailored CO₂ purification strategies, prompting questions around suitable metallurgy, responses to upset conditions, and ways in which industry can support regulators in making cost-effective decisions.

Ray McKaskle opened his presentation by addressing one of the foundational steps in CO₂ purification, dehydration. Removing water from CO₂ streams is crucial for several reasons, including preventing ice and clathrate formation.

Ray further highlighted the effects of oxygen contamination, likening oxygen to “the kid that brings beer to an already chaotic teenagers’ party,” due to the havoc it wreaks in CCS systems. Oxygen, especially in combination with water, increases corrosivity in CO₂ streams. Additionally, oxygen can oxidise TEG (triethylene glycol), leading to faster solvent degradation, promote biological growth, and react with H₂S to form elemental sulphur, sulfuric acid, or other corrosive sulphur compounds.

Ray emphasized the pertinence of upstream improvements in enhancing the efficiency and feasibility of CO₂ capture and conditioning processes. He elaborated on the importance of improving or incorporating advanced pollution control equipment upstream, which not only streamlines CO₂ capture by removing or reducing contaminants but also yields the ancillary benefit of curbing other pollutant emissions.

The second speaker, John Woods continued the discussion by focusing on the selection of cost-effective CO₂ conditioning technologies. He began by reviewing typical CO₂ impurities found in carbon capture feeds, citing examples of CO₂ pipeline specifications and liquid CO₂ shipping requirements. This provided context for selecting conditioning methods tailored to specific project needs.

John then shared a methodology for selecting treatment steps, emphasising the importance of cost-effective removal processes, especially for challenging impurities like oxygen. He outlined several purification technologies and identified well-established methods and areas where knowledge gaps remain e.g., Handling heavily contaminated CO₂ streams using specialist adsorbents and catalysts, effective removal of BTEX compounds, hydrocarbons, and volatile organic compounds (VOCs), membrane separation techniques for contaminants in CO₂ streams, understanding hydrate formation temperatures in CO₂ mixtures containing impurities and identifying contaminants that could interfere with or poison catalysts and adsorbents.

Richard Porter highlighted the various risks associated with CO₂ impurities, categorising them into physical and chemical risks that can impact the stability and efficiency of CO₂ storage. The physical risks he discussed include decompression in depleted gas fields and the risk of hydrate formation, both of which can affect the fluid dynamics and storage efficacy within the subsurface. Chemical risks include reservoir impact, where impurities alter the chemical composition of reservoir fluids, and caprock integrity, where chemical interactions could compromise the caprock, increasing the risk of CO₂ leakage.

Richard also addressed strategies to mitigate CO₂ impurity impacts on storage, emphasising the importance of accurate modelling, reactive flow simulations, and refining injection strategies. In his concluding remarks, he proposed potential solutions, including tailored specifications for different segments of the CCUS chain to enable cost reductions, such as through shared purification infrastructure. He also called for further research on impurity management, including the development of impurity-tolerant catalysts for CCU applications, and refined injection strategies to manage impurities in CO₂ storage effectively.

Final Thoughts

The insights shared in the Technical Panel Session on “Strategies for CO₂ Purification” provided a rigorous view of the technical and economic challenges involved. Owain Tucker did a fantastic job in setting the scene of the discussion that followed by emphasising the complex challenges posed by multiple contaminants, while Ray McKaskle underscored the importance of impurity management and methods tailored to different sources. John Woods focused on selecting cost-effective conditioning technologies, and Richard Porter highlighted the physical and chemical risks impurities pose to CO₂ storage, advocating for accurate modelling and tailored solutions.

In conclusion, this panel highlighted the nuanced requirements of CO₂ purification, underscoring the need for innovative, flexible technologies and collaborative approaches across the industry.