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The Missing Link

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3 June 2024

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First featured on Bunkerspot

As momentum builds on the use of carbon capture and storage to accelerate the energy transition, Eng Kiong Koh of the Global Centre for Maritime Decarbonisation discusses the findings of its recent report on possible offloading pathways for CO2 captured onboard vessels with Lesley Bankes-Hughes.

Carbon capture and storage (CCS) is playing an increasingly important role in the energy transition narrative. While its critics may say that capturing and sequestering carbon from industry’s emissions is not in the true spirit of decarbonisation, the fact is that CCS offers a way (in the short and medium term) of mitigating some of the climate damage wrought by fossil-based fuels, thus making 2050 climate targets more achievable. However, the volumes of CO2 that must be squirreled away in underground caverns or beneath the sea are not insignificant. According to the International Energy Agency (IEA) some 6 billion tonnes of CO2 will need to be captured and stored a year in 2050 in order to reach its net zero scenario.

However, many CCS projects are in train around the world. Energy giants, like ExxonMobil and Saudi Aramco, are two such industry players with ambitious CCS plans. The Northern Lights project, a joint venture between Equinor, Shell and TotalEnergies, is a high-profile initiative which will demonstrate the storage of captured CO2 on the Norwegian Continental Shelf.

Shipping will play a critical role in transporting CO2 from the industrial ‘emitters’ to sequestration locations and the Northern Lights partners have already placed an order for four 7,500 cubic metre LNG-fuelled CO2 tankers with Dalian Shipbuilding Offshore Co in China. Other liquid CO2 carriers are also in prospect. At the time of writing, in mid-May, Deltamarin and CCS company Ecolog had just unveiled a dual fuel LNG CO2 carrier design.

The logistics of moving captured CO2 around the world are challenging but certainly not impossible. As Mark Williams, MD of Shipping Strategy and contributing editor at Bunkerspot’s sister publication, ship.energy, recently noted, to ship one billion tonnes of CO2 would require 0.9 billion cubic metres of shipping capacity over 25 years. This, said Williams, would make CO2 shipping about as common as iron ore shipping. According to his estimates, a fleet of around 800 to 1,000 liquefied CO2 tankers by 2050 should be sufficient. By way of comparison, he points to the 1,100 ‘standard’ Capesizes of around 160-180,000 DWT.

Captured carbon can be sequestered or it can be used as a feedstock in a range of industrial processes, including the production of chemicals, food and, indeed, the ‘blue’ variants of marine fuels.

Also in mid-May, ADNOC delivered what it described as ‘the world’s first certified bulk commercial shipment of low-carbon ammonia enabled by carbon capture and storage (CCS)’ to Mitsui in Japan. The cargo was sourced from Fertil, Fertiglobe’s 100%-owned facility located in the Ruwais Industrial City, Abu Dhabi and Mitsui will use it for clean power generation in Japan.

Shipping is, of course, also a GHG emissions ‘culprit’, responsible for around 3% of global emissions, and while the CCS on land is moving forward (albeit that many Final Investment Decisions (FIDs) for such projects are still awaiting the green light), feasibility studies – and some projects – are now just underway on onboard carbon capture and storage (OCCS).

GCMD’s study on offloading onboard captured carbon dioxide

A recent study, scoped and commissioned by the Singapore-based Global Centre for Maritime Decarbonisation (GCMD), and prepared by Lloyd’s Register and Arup, looked at a small, but critical part of the wider CCS chain – the offloading of onboard captured CO2.

The concept study looked at four offloading concepts: offloading captured and liquefied CO2 from a ship to a liquid bulk terminal; from a ship to a floating CO2 storage unit through an intermediate receiving vessel; from a ship to a liquid bulk terminal through an intermediate receiving vessel; and in ISO tank containers from a ship to a terminal.

Some of the key takeaways of this in-depth, technical report were that the best option for the movement and offloading of CO2 is in a liquefied form, and of the four offloading concepts, ship to ship and ship to shore transfers using intermediate CO2 receiving vessels are the most scalable, particularly if the volumes of captured CO2 are large and that CO2 is destined for sequestration or to be used as a feedstock for producing synthetic fuels.

Given current limitations of port readiness and existing infrastructure, the study found that ship to terminal transfer of liquefied carbon dioxide (LCO2) in ISO tank containers would be the easiest modality to pilot now. Onboard storage in Type C tanks is also seen as feasible solution.

The report also highlighted that while class societies have developed rules and guidelines for the design of vessels, there are as yet no maritime regulatory standards for OCCS and the offloading of LCO2 .

The pressures required to liquefy and store CO2 are also considered, as are the impacts of impurities in CO2 on storage and pipelines, and the challenges of capturing CO2 emissions from the combustion of different bunker fuels.

One of the report’s conclusions is that there is a need to link onboard captured CO2 to the onshore CCUS value chain. Also, if OCCS is to be successfully adopted it will require ‘a compelling economic case, updated regulations, infrastructure development and consensus on standards and guidelines.’

Eng Kiong Koh, Director in the Projects team at the GCMD, is the organisation’s lead in looking to unlock the carbon value chain initiative to demonstrate onboard carbon capture and storage systems and the offloading of LCO2. Talking to Bunkerspot, he explains the rationale behind the concept study.

Addressing the gap in the carbon capture value chain

‘When you look at land-based carbon capture systems, many projects are coming online to permanently sequester captured CO2. In this value chain, shipping is one of the modes to transport CO2,’ he said. ‘However, the link between offloading captured CO2 from ships to shore is missing, and this very gap is what the report is aiming to address.’

While individual CO2 offloading technologies may already be commercially available, Koh argues that a systemic approach to integrate these technologies is not yet mature.

He further explains, ‘Most CO2 transfers today primarily involve from ship to terminal or from terminal to ship. However this approach is limited by the number of jetties equipped for CO2 handling, hindering our ability to scale operations. An alternative approach using ISO tank containers presents a different challenge: the need to offload hundreds of containers, and then replacing these empty ISO tank containers.



‘These receiving vessels will then transport the CO2 to another designated terminal for offloading or to a floating storage facility that need not be located nearby.’

However, as Koh acknowledges, using this logistics ‘model’ with receiving vessels and floating storage will increase capex and opex.

Operational and safety considerations handling LCO2

Maintaining the purity of the CO2 is another critical factor, not only because of the onboard impact when impurities are present but also in relation to the end use of the CO2. For example, when used as a feedstock for the production of synthetic fuels, a minimum 95% level of CO2 purity is required.

One challenge caused by compromised purity can be corrosion, says Koh, and this is a concern for vessel assets which have long lifespans, so finding suitable materials is key. Toxicity can also be a problem, caused by the presence of hydrogen sulphide or sulphur dioxide in the CO2.

Impurities can also increase the saturation pressure, and this is particularly challenging when operating at low pressure, he highlights.

‘In the presence of impurities, even minor changes in temperature and pressure can cause CO2 to gasify or solidify from its liquid state. To avoid this triple point scenario, where CO2 can exist as a mixture of solid, liquid and gas, shipowners typically resort to storing CO2 at higher pressures.’

‘The triple point of CO2 is at 5.18 bar and -56.6 oC. Low pressure operations takes place between 5.7 – 10 bara, which is very near the triple point. Some companies opt for medium pressure operations, typically between 14 to 19 bara, and we have also seen companies adopting 20 bara to avoid encountering the triple point scenario.’

When asked about the impact of capturing carbon on engine load and vessel weight, Koh thinks these are manageable issues, noting that vessel owners and designers will have gone through Hazard and Operability analysis (HAZOP) and approached class societies to ensure that a tank is placed in such a way that the increased weight resulting from captured CO2 and its associated hardware will not affect overall stability, and also to determine a safety zone for its placement – whether on the bridge side or the cargo side of a tanker.

The report suggests that the Ro-Ro segment using ISO tank containers could be a feasible candidate for OCCS. In terms of suitability for other vessel types, Koh points to the space needed onboard for storage as one constraint. Onboard carbon capture will also increase fuel consumption due to the energy needs to regenerate amine, and compress, liquefy and store CO2 in a liquid form.

Retrofitting vessels to become LCO2 carriers

The report also looked at the possibility of retrofitting vessels to become LCO2 carriers, and it determined that there could be a few gas ships currently in service that could be repurposed as carriers given that their cargo tanks are designed for 7 bar, and they can store LCO2 at low pressure. However, one caveat would be that the cargo tanks’ structure and tank supports would have to be reevaluated to see if they are suitable for the higher cargo density of LCO2.

Adding a receiving vessel between the supply vessel and the terminal/floating storage unit adds another link in the delivery chain and also begs the questions of what is the optimal type and size of the receiving vessel.

The first consideration is pressure, says Koh. ‘For low LCO2 storage capacities, storage at medium pressure is preferable to avoid phase changes at the triple point,’ he explains.

Gauging the optimum size of the receiving vessel is also a challenge. While the Northern Lights partnership ordered a quartet of 7,500 cubic metres ships, Koh points out a critical question: storage. ‘Would you be able to receive captured CO2 once, twice, or multiple times before you return to the terminal to offload?’

Furthermore, the challenges don’t end once captured carbon dioxide has been transferred from the ‘capturing’ vessel to the receiving ship. ‘At the terminal, you will be using large tanks to maximise storage capacity, which suggests low-pressure systems, he says. ‘That presents some challenges to change over from medium to low pressure.

‘I think it can be done,’ Koh adds, ‘but it probably means additional cost.’

The bigger picture for onboard captured CO2

While the report is focused on how to bridge the gap between capturing CO2 onboard a seagoing vessel and transferring it to a terminal, Koh emphasises the importance of looking at the bigger picture, which includes sequestration and the potential end use of the CO2. The customers’ requirements for the captured CO2 will drive capture and subsequent processes, he says.

‘Let’s say the end customer requires high-quality CO2 and achieving this may be difficult. In such cases, a processing plant offering a service to clean up the gas may be required.’

Looking at the technological readiness for onboard carbon capture, Koh says innovative work is underway to reduce the size of the equipment as well as the energy needed for the process.

‘The technology for carbon capture is maturing very fast with many ongoing trials,’ he comments, ‘I think the challenges are technical in nature and can be resolved if one can afford the space and the energy.’

So what is putting the brakes on OCCS adoption? Koh identifies immature regulations and nascent business models as bottlenecks: Can CO2 actually be offloaded? How should captured CO2 be categorised – as waste or a feedstock? If it’s a feedstock delivered to an end user, is the shipowner providing a product or a service?

The International Maritime Organization (IMO) must put regulations in place to address these issues, says Koh, ‘because captured CO2 can’t just be offloaded anywhere, it must have an avenue to be sequestered. But I see this as something that will come eventually.’

Adapting OCCS to different marine fuels

Of course, as the energy transition progresses, ships will increasingly be dual-fuelled and OCCS will have to capture the CO2 emissions from different bunker fuels, and this will dictate the onboard technologies to be deployed.

As Koh explains, ‘LNG offers an advantage for OCCS because its emissions are low in particulate matter and do not contain sulphur dioxide (SOx), which can deactivate the amine that is used to capture CO2. However, heavy fuel oil (HFO) remains the more common choice due to its lower cost and faster payback for the OCCS technology. Capturing emissions from HFO combustion, though, will require pre-treatment of the emissions to remove SOx among other pollutants before CO2 can be captured.’



‘Even with marine gasoil, you cannot assume that the SOx emissions are sufficiently low for an inline system to operate without deactivating amine-based solvents used for carbon capture.

While there has not been much work thus far on the use of methanol with OCCS, Koh says that, in comparison with heavy fuel oil, ‘its emissions are cleaner.’

Developing standards for OCCS

In looking at the development of a supply infrastructure for alternative fuels there has been an emphasis on standardisation, and when it comes to OCCS, Koh suggests that a standards-based approach should be relatively straightforward.

‘OCCS can leverage existing land-based standards and develop maritime-equivalent standards to operationalise OCCS, so we don’t see this as a major obstacle.’ he says.

Scale of OCCS critical for widespread adoption

While work is ongoing to develop and mature the technologies to link the vessel at sea with landside/floating storage, a fundamental question is what will be the scale of demand for OCCS?

Annual global bunker consumption is currently estimated to be between 250-300 million tonnes, which in turn produces CO2 emissions totalling 750-900 million tonnes.

‘Realistically, not everyone is going to use carbon capture,’ Koh comments.

‘Fuel oil projections suggest that between one tenth to one fifth of its use is expected by 2050. If we then assume that between one tenth to a fifth of fuel oil use will deploy OCCS, we might be looking at capturing and transporting around 300 million tonnes of CO2.

‘300 million tons of CO2 may sound substantial, however, compared to projections suggesting a need for capturing 6 billion tons annually in 2050, it’s a drop in the ocean.’ Koh proposes joining forces with land-based carbon capture partners to leverage their infrastructure for economies of scale and efficiency’

‘You need to ask how much will be offloaded every day and every year to justify the investment into the infrastructure.’

As international shipping embarks on its steep learning curve about carbon trading with its inclusion in the EU’s Emissions Trading System, Koh also reminds that the captured carbon comes with a price, and this cost, he suggests, ‘will be a very critical determinant in terms of using carbon capture.’

Despite these challenges, Koh remains optimistic. He echoes the findings of the IEA’s latest report on CCUS, which highlight the emergence of new ‘part-chain’ business models. These models involve separate entities specialising in different parts of the CCUS value chain to bolster innovation and reduce costs across the entire chain. ‘This is precisely what GCMD is doing, he says, ‘contributing to a knowledge base required to scale up CCUS to help reach net zero goals.’













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