Captain Akshat Arora, Senior Risk Assessor at Skuld has written an in-depth piece on shipboard carbon capture, which he said was “a technology that has the potential to play a significant role in maritime decarbonization”.
However, its success would depend on a number of factors, including:
- technical advancements (to produce systems compatible with shipboard operations and available space);
- commercial feasibility (which will in turn be impacted by the availability and cost of alternative fuels, as well as the price of carbon);
- the regulatory landscape.
Land-based carbon capture projects have shown that the carbon-footprint reduction potential of such technologies could be significant, but the cost element was currently high.
The article provides an overview of this emerging technology and evaluates how carbon capture, utilization, and storage technologies might be applied in the maritime sector.
As a part of establishing a path to net zero by or around 2050 , there has been increasing pressure on the maritime sector to minimize its greenhouse gas (GHG) emissions. These reduction targets are driving the industry to pursue various feasibility pathways for greener fuel options, such as ammonia and methanol. However, this energy transition may take decades.
In the meantime, there has also been a growth in interest in various decarbonization technologies, including the use of carbon capture and storage on board vessels
Onboard Carbon Capture Utilization and Storage (OCCUS) could assist in reducing the environmental impact by capturing carbon dioxide (CO2) emissions from ships before they are released into the atmosphere with exhaust gas. The captured CO2 emissions are then liquefied and transported away either to be stored deep underground or transformed into value-added products.
Although this process has been used by other industries, it has not yet been widely adopted by the marine industry. This is due to the additional costs and space constraints that make it difficult to install the necessary equipment on board. However, Captain Arora noted that technological developments and innovative design solutions could potentially overcome these challenges and make OCCUS a viable option for existing ships. It would also provide a route to extending the asset lifetime of vessels where converting to zero emissions would either be impossible or prohibitively expensive.
Among the several potential carbon-capturing technologies, the most successful approach for ship-based carbon capture is the application of the post-combustion method. This procedure entails cleaning exhaust gases before they are released, typically by installing equipment within or near the vessel exhaust stack.
The following measures being considered by the shipping industry are (full details in full article, link below):
- Chemical absorption
- Membrane separation
- Cryogenic capture
- Solid sorbent adsorption
In terms of storage and handling of captured carbon, liquefaction of CO2 on ships may be the most appropriate approach, taking into account space limitations ,as well as the convenience of handling liquid cargo. The captured CO2 would need to be stored onboard as a liquid in pressurized and insulated tanks to maintain cryogenic conditions. This means that there could potentially be some compromise on the available cargo space on the ship.
Liquid CO2 has properties similar to liquefied petroleum gas (LPG). Pressurized tanks can manage liquid CO2 boil-off up to certain design pressures, after which pressure relief and boil-off gas reliquefication are commonly applied. The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) specifies Type C liquefied gas tanks as the current standard for pressurised CO2 storage.
CO2 is less toxic when compared to hydrocarbon, and is also not flammable. However, Captain Arora warned that the purity of CO2 contained in Type C tanks would need to be carefully monitored, as impurities might cause corrosion in the storage system.
Ships would need to discharge the liquid CO2 to either shore reception facilities or an offtake CO2 tanker for transfer to utilization hub or facility where the captured CO2 can then be either used in the industry or injected back into the earth.
In November 2021, Stena Bulk and OGCI (Oil and Gas Climate Initiative) conducted a combined study to analyse energy balances, fundamental physics, and integration problems on a medium-range (MR) oil/chemical tanker, a Suezmax crude oil tanker (both running on heavy fuel oil (HFO)), and an LNG carrier (fuelled by LNG).
The findings of the study showed that the LNG carrier offered the simplest and most straightforward path to a feasible carbon capture system because it uses an engine type that delivers sufficient waste heat in the exhaust gas, uses fuel with no impurities, and offers infrastructure on board that could be beneficial when liquifying and storing the captured CO2 through cryogenic carbon capture technology. However, a system that proved feasible on this type of ship may not be easily adapted to other ships.
The study’s findings also indicate that carbon capture and storage on a large tanker is technically viable. The technology used for the Suezmax tanker was chemical absorption using monoethanolamine (MEA) to capture the carbon. The main challenge was the cost of installation and operation, with storage tanks, compressors, and other equipment requiring significant upfront capital expenditure (capex).
According to the analysis, operating costs would also rise as a result of the energy necessary to operate the system effectively. However, the study discovered that these costs might be significantly reduced if the engine was adapted for compatibility with carbon capture and storage.
Typically, the costs would depend on the amount of carbon that is required to be captured and the opportunity for the ship to be able to discharge the captured liquid CO2 to a reception facility. The study concluded that these costs were likely to be a hurdle to the deployment of this system in the near and medium term, but that as the technology improves and becomes cheaper to operate, it could become a viable option for the industry’s decarbonization pathway.
In July 2023 a ship-based carbon capture (SBCC) prototype developed under the EverLoNG project (led by the Dutch research and development organization TNO) was installed on an LNG-powered LNG carrier owned by Total Energies. The objective is to achieve a 70% reduction in CO2 emissions from ships, taking the same ship running on LNG but not equipped with SBCC as the reference case.
A pivotal facet of the project revolves around enhancing the cost-effectiveness of SBCC. The target is to drive down the expenses associated with onboard carbon capture and storage to below 100 €/ton for initial implementations by the year 2025, and an even more cost-efficient 50 €/ton for subsequent implementations.
However, Captain Arora noted that a key element missing from these analyses was the port-side infrastructure necessary to offload and process the captured CO2. “Although some ports and locations are equipped to handle CO2 shipments for industrial use and large-scale recycling and sequestration operations, most ports are not set up to manage this process”, he warned.
As a result, joint ventures such as the Northern Lights, a tie-up between Equinor, Shell and TotalEnergies, are building ships capable of transporting the captured and liquefied CO2 from several emitters to an onshore storage terminal on the Norwegian west coast.
From there, the liquefied CO2 will be transported by pipeline to an offshore storage location subsea in the North Sea, for permanent storage. According to their recent announcement, three dedicated CO2 carriers, each with a cargo size of 7,500 m3 and a length of 130 m are being built in Dalian, China. The first two ships are scheduled to be delivered in 2024 and will be operated by K-Line on behalf of Northern Lights.
Ecolog is looking to develop specialised liquid CO2 carriers between the range of 20,000 m3 and 84,000 m3; and Mitsui O.S.K. Lines (MOL) and the Kansai Electric Power Co. (KEPCO) have signed a Memorandum of Understanding (MoU) to study marine transportation for the development of a CO2 capture and storage (CCS) value chain.
More recently, based on the study done by Rystad Energy, 55 vessels will be required by 2030 for the emerging CO2 transport and storage.
Because liquefied CO2 transportation is still in its early phases, the industry is highly unstandardized. Each project is unique, and a variety of vessel sizes and types have been proposed.
The International Maritime Organization (IMO) has recognized this gap, and during theMEPC-80 meeting in July 2023 it was agreed to review and consider a way forward to potentially accommodate onboard CO2 capture within IMO’s regulatory framework.
Captain Arora concluded that OCCUS was technically feasible, but said that it might require significant additional capital expenses and some compromise on cargo space. The system was energy-intensive and the annual operating costs for the ships would go up considerably, depending on the amount of carbon they captured. The regulations and technologies were still developing, but the various pilot projects should provide an opportunity to assess the technical feasibility and to help assess the economic feasibility.
 MEPC-80 (3-7 July 2023) adopted 2023 revised IMO GHG Strategy. Read here – https://www.ukpandi.com/news-and-resources/articles/2023/mepc-80-a-summary/
 Clarksons has reported that dedicated CO2 carriers are being built, with tanks capable of withstanding up to 20 bar pressure and -80C temperature.
 Can CO2-EOR really provide carbon-negative oil? – Analysis – IEA