Onboard carbon dioxide capture cannot fully replace the transition to low-carbon fuels in maritime transport. However, it could reduce greenhouse gas emissions by nearly half and serve as an intermediate solution on the path to shipping decarbonization. This is the conclusion reached by researchers from the Jülich Research Center in Germany and Leiden University in the Netherlands, who for the first time evaluated the performance of such systems on two real sea vessels.
The study examined two actual ships with different operating conditions: a large LNG carrier transporting liquefied natural gas (LNG) from the United States to the Netherlands, and Sleipnir – one of the world’s largest floating cranes – engaged in offshore platform installation in the North Sea. The analysis used real engine operating data spanning several years, including load profiles and methane emission patterns, as well as results from CO₂ capture system trials conducted within the frame of the EverLoNG project. This allowed the calculations to closely approximate real operational conditions.
The technology’s operating principle closely resembles systems already used at power plants. Exhaust gases are passed through a solution that absorbs carbon dioxide. The CO₂ is then separated, liquefied, stored in onboard tanks, and sent for permanent geological storage after the ship arrives at the destination port.
When considering only emissions from the ship’s funnel, the technology appears highly effective: it captures 72–82% of the CO₂ produced. However, the system itself requires additional energy to operate. The solvent must be heated, CO₂ compressed, fluids pumped, and the captured gas stored until offloading at the port of arrival. As a result, fuel consumption increases. The magnitude of this increase depends heavily on vessel design. For the LNG carrier, additional fuel consumption reached about 15%, whereas for Sleipnir it was only 5–6%, since that vessel was able to utilize waste heat from exhaust gases instead of an auxiliary boiler.
When the researchers accounted for the full life cycle of the technology – from fuel extraction and transport to shipping and geological storage of the captured CO₂ – the net effect proved considerably lower. Depending on vessel type and operating conditions, the overall greenhouse gas emission reduction ranged from 32% to 55%; with regard to the two vessels examined, the figures were approximately 40% and 46%.
One of the study’s most important findings was the role of methane slip. In many cases, this proved to be the primary factor limiting the technology’s effectiveness. This is particularly relevant for LNG-powered vessels: when unburned methane escapes into the atmosphere, the climate benefit of CO₂ capture is significantly diminished.
The researchers also assessed whether the new technology creates additional environmental problems. Due to higher fuel consumption, emissions of nitrogen oxides, ammonia, and certain other pollutants slightly increase. For most environmental impact categories, this increase ranged from 5% to 25%. In the researchers’ view, however, such changes are not significant enough to call into question the viability of onboard CO₂ capture.
Overall, the study showed that the technology’s effectiveness is determined by the specific characteristics of each vessel – engine type, operating profile, availability of waste heat recovery, and even the shipping route. Installing such systems without prior calculations is therefore not feasible. Moreover, widespread adoption would require building a comprehensive infrastructure for receiving, transporting, and geologically storing captured CO₂ at ports. This is precisely why the researchers view onboard capture not as a replacement for low-carbon fuels, but as an intermediate technology that can help reduce emissions in the coming decades, while alternative fuel production and the necessary infrastructure are still being developed.
