ClassNK has published the second edition of its Guidelines for Onboard CO2 Capture and Storage Systems, introducing the ‘world’s first’ requirements for on-board systems using membrane separation technology.
The new edition builds on ClassNK’s 2023 publication, which focused primarily on amine-based absorption systems. The new version broadens the scope to include membrane separation, a technology that requires less energy and avoids the use of amine solution. According to ClassNK, this approach could be more adaptable across a wider range of vessel types.
The guidelines consolidate common requirements across different capture technologies and include a set of generic safety and functional requirements intended to apply across different CO2 capture methods. These updates aim to support the safe design, manufacturing, and installation of OCCS equipment, while aligning with ongoing regulatory and technical developments.
CO2 captured at sea is not yet formally recognised under measures such as the Energy Efficiency Existing Ship Index (EEXI) or Carbon Intensity Indicator (CII). However, the International Maritime Organization (IMO) has begun work on a regulatory structure that could bring such systems within scope. The eventual inclusion of OCCS in compliance mechanisms could significantly influence investment and deployment decisions.
Chemical absorption remains the most mature technology, having been widely deployed on land for power plant exhaust treatment. However, its high energy demand for solvent regeneration poses operational challenges. By contrast, membrane separation relies on polymer membranes and pressure differentials to isolate CO2, a process that avoids heating and cooling cycles and could therefore offer efficiency gains.
ClassNK says the guidelines will be reviewed when necessary, considering the ongoing discussions at IMO and the International Association of Classification Societies (IACS), as well as developments in relevant technologies. The organisation’s move reflects growing efforts among classification societies and technology developers to codify safety and performance standards for OCCS systems.
